feat(scripting): out-of-process pre-emptible script runner behind Scripting:Runner (lmxopcua#780 P1)

Opt-in (Scripting:Runner=OutOfProcess; InProcess stays the default and its code path is unchanged). Implements
the P1 slice of docs/plans/2026-11-09-out-of-process-script-runner-design.md with the owner's §14 decisions:

- Options: Scripting:Runner (InProcess | Shadow | OutOfProcess), Scripting:Runner:Seams, Scripting:Worker:*
  (Shards 2, HardGrace max(1 s,T), HeapLimitBytes 512 MiB, QuarantineAfterKills 2, UnavailableGrace 5 s,
  IsolationProbationRuns 20, PeCacheDir validated absolute + outside the content root (fail closed),
  ExecutablePath). Shadow is not implemented yet: runs InProcess with a startup Warning.
- Core.Scripting: IScriptRunner seam + InProcessScriptRunner (today's guard, the parity baseline).
- Core.Scripting.Protocol: protobuf envelopes, 4-byte LE framing (zero/oversize/truncated/garbage refused),
  Variant carrying the exact CLR type; unsupported types are explicit failures.
- ScriptWorker app: compiles in the worker, P-thread scheduler, host-driven soft cancel, fail-fast
  watchdog, heartbeats, ctx.Logger forwarding, exits on pipe EOF / parent gone, forbidden-assembly
  self-check; Akka and Grpc.Core.Api excluded from its folder. Shipped in script-worker/ (Build + Publish).
- Core.Scripting.OutOfProcess: K shards + isolation worker, soft T / hard T+G kill, attribution
  (deadline kill = one key; crash = suspects -> isolation; isolation crash = strike), kill-strike
  quarantine, backoff 250 ms -> 30 s, fail closed, cleared allow-listed env, nonce + pid handshake on a
  current-user pipe, Windows Job Object.
- VirtualTag + Calculation seams use the runner when selected; a runner-side failure (worker restarted /
  runner unavailable) publishes BadResourceUnavailable (0x80040000) — ScadaBridge#112. Script faults keep
  BadInternalError. The scripted-alarm seam stays in process (alarms last).

Tests: new ZB.MOM.WW.OtOpcUa.ScriptWorker.Tests (Category=ScriptWorker, real processes; green on macOS and
on windev/Windows), seam tests in Host/Runtime/Calculation suites; mutation-checked.

Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV

CLAUDE.md

@@ -388,3 +388,10 @@ endpoints under `/api/script-analysis/*`, gated by the `ConfigEditor` policy
 `ScriptAnalysisEndpoints.MapScriptAnalysisEndpoints`).
 `Core.VirtualTags` is now just `DependencyGraph`, `ITagUpstreamSource` and `IHistoryWriter` — the dormant `VirtualTagEngine`/Source/Definition and `TimerTriggerScheduler` were deleted.
 See `docs/ScriptEditor.md` for the full guide. Scripts may use the `{{equip}}` token for equipment-relative tag paths that resolve per-equipment at deploy time — see the "Equipment-relative tag paths" section in `docs/ScriptEditor.md`.
+
+**Out-of-process script runner (lmxopcua#780, opt-in).** `Scripting:Runner` = `InProcess` (default, unchanged) | `OutOfProcess` | `Shadow` (not yet).
+`OutOfProcess` runs the VirtualTag + Calculation seams' compiled scripts in `ZB.MOM.WW.OtOpcUa.ScriptWorker` processes
+(`src/Core/ZB.MOM.WW.OtOpcUa.Core.Scripting.OutOfProcess`, protocol in `Core.Scripting.Protocol`), shipped in `script-worker/`
+beside the host; a runner-side failure publishes `BadResourceUnavailable` (ScadaBridge-visible, ScadaBridge#112). The worker tests
+are `tests/Server/ZB.MOM.WW.OtOpcUa.ScriptWorker.Tests` (`Category=ScriptWorker`, real processes). See `docs/VirtualTags.md`
+§"Out-of-process runner".

ZB.MOM.WW.OtOpcUa.slnx

@@ -8,6 +8,8 @@
     <Project Path="src/Core/ZB.MOM.WW.OtOpcUa.Core/ZB.MOM.WW.OtOpcUa.Core.csproj" />
     <Project Path="src/Core/ZB.MOM.WW.OtOpcUa.Core.Scripting.Abstractions/ZB.MOM.WW.OtOpcUa.Core.Scripting.Abstractions.csproj" />
     <Project Path="src/Core/ZB.MOM.WW.OtOpcUa.Core.Scripting/ZB.MOM.WW.OtOpcUa.Core.Scripting.csproj" />
+    <Project Path="src/Core/ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol/ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol.csproj" />
+    <Project Path="src/Core/ZB.MOM.WW.OtOpcUa.Core.Scripting.OutOfProcess/ZB.MOM.WW.OtOpcUa.Core.Scripting.OutOfProcess.csproj" />
     <Project Path="src/Core/ZB.MOM.WW.OtOpcUa.Core.VirtualTags/ZB.MOM.WW.OtOpcUa.Core.VirtualTags.csproj" />
     <Project Path="src/Core/ZB.MOM.WW.OtOpcUa.Core.ScriptedAlarms/ZB.MOM.WW.OtOpcUa.Core.ScriptedAlarms.csproj" />
     <Project Path="src/Core/ZB.MOM.WW.OtOpcUa.Core.AlarmHistorian/ZB.MOM.WW.OtOpcUa.Core.AlarmHistorian.csproj" />
@@ -15,6 +17,7 @@
   <Folder Name="/src/Server/">
     <Project Path="src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/ZB.MOM.WW.OtOpcUa.AdminUI.csproj" />
     <Project Path="src/Server/ZB.MOM.WW.OtOpcUa.ControlPlane/ZB.MOM.WW.OtOpcUa.ControlPlane.csproj" />
+    <Project Path="src/Server/ZB.MOM.WW.OtOpcUa.ScriptWorker/ZB.MOM.WW.OtOpcUa.ScriptWorker.csproj" />
     <Project Path="src/Server/ZB.MOM.WW.OtOpcUa.Host/ZB.MOM.WW.OtOpcUa.Host.csproj" />
     <Project Path="src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/ZB.MOM.WW.OtOpcUa.OpcUaServer.csproj" />
     <Project Path="src/Server/ZB.MOM.WW.OtOpcUa.Runtime/ZB.MOM.WW.OtOpcUa.Runtime.csproj" />
@@ -91,6 +94,7 @@
   <Folder Name="/tests/Server/">
     <Project Path="tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/ZB.MOM.WW.OtOpcUa.AdminUI.Tests.csproj" />
     <Project Path="tests/Server/ZB.MOM.WW.OtOpcUa.ControlPlane.Tests/ZB.MOM.WW.OtOpcUa.ControlPlane.Tests.csproj" />
+    <Project Path="tests/Server/ZB.MOM.WW.OtOpcUa.ScriptWorker.Tests/ZB.MOM.WW.OtOpcUa.ScriptWorker.Tests.csproj" />
     <Project Path="tests/Server/ZB.MOM.WW.OtOpcUa.Host.IntegrationTests/ZB.MOM.WW.OtOpcUa.Host.IntegrationTests.csproj" />
     <Project Path="tests/Server/ZB.MOM.WW.OtOpcUa.Host.Tests/ZB.MOM.WW.OtOpcUa.Host.Tests.csproj" />
     <Project Path="tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.IntegrationTests/ZB.MOM.WW.OtOpcUa.OpcUaServer.IntegrationTests.csproj" />

docs/ScriptEditor.md

@@ -211,6 +211,11 @@ scripted-alarm predicates) runs scripts through the shared `ScriptRunGuard`:
   `Scripting:MaxAllocBytesPerRun` (64 MB) is quarantined. This is sampled after the
   run returns, so a run that OOMs the process first is not stopped — that needs an
   out-of-process runner (→ #750).
+- **Out of process (opt-in, lmxopcua#780).** `Scripting:Runner=OutOfProcess` moves the
+  virtual-tag and Calculation seams' compiled runs into `ScriptWorker` processes, where a
+  run past `T + Scripting:Worker:HardGrace` is stopped by killing its worker and an OOM
+  kills a worker instead of the server. A run whose worker died under it reads
+  `BadResourceUnavailable`. See `docs/VirtualTags.md` §"Out-of-process runner".
 - **Recursion.** Unbounded recursion fails the script with
   `ScriptStackExhaustedException` (Bad, script log) instead of overflowing the
   stack, which would terminate the whole server. The runtime compile inserts a

docs/ServiceHosting.md

@@ -88,6 +88,16 @@ and supply `ServerHistorian__ApiKey` via the environment on the OtOpcUa host sid
 `historian:write` + `historian:tags:write`. See [Historian.md](Historian.md) for the full config-key and
 deployment-prerequisite reference. (The retired Wonderware TCP sidecar: [Historian.Wonderware.md](drivers/Historian.Wonderware.md).)
 
+## Script worker processes (`Scripting:Runner=OutOfProcess`, lmxopcua#780)
+
+Off by default. When enabled, a driver node launches up to `Scripting:Worker:Shards` + 1 child processes
+(`ZB.MOM.WW.OtOpcUa.ScriptWorker`, from `script-worker/` beside the host) on its first compiled script evaluation and
+kills them with it: a Job Object with kill-on-close on Windows, pipe end of stream plus a parent-pid poll elsewhere,
+and a Shutdown frame then a kill on host stop. Their stderr lands in the host log prefixed `ScriptWorker[<shard>]`.
+The worker currently runs under the host's account through the dotnet muxer; the dedicated low-privilege account,
+pipe ACL and firewall outbound rule (design §14 #5/#6) are installer work still open on lmxopcua#780. See
+`docs/VirtualTags.md` §"Out-of-process runner".
+
 ## Install / Uninstall
 
 - `scripts/install/Install-Services.ps1 -Roles admin,driver` — installs `OtOpcUaHost`.

docs/VirtualTags.md

@@ -37,11 +37,54 @@ User scripts are compiled via `Microsoft.CodeAnalysis.CSharp` (regular compiler,
 
 #### Known resource limits (accepted trade-offs)
 
-The sandbox cannot pre-empt a script. **Memory:** each run's own-thread allocation is sampled (`GC.GetAllocatedBytesForCurrentThread`) and a run over `Scripting:MaxAllocBytesPerRun` (default 64 MB) quarantines the script — but the sample is taken after the run returns, so a script that allocates fast enough (`new byte[int.MaxValue]` in a loop) can still OOM the process first. **CPU:** a tight loop keeps its pool thread after the timeout fires; `ScriptRunGuard` bounds that to one orphan per script by refusing further runs while it spins (Bad `"previous evaluation still running"`) and quarantines after three consecutive timeouts (a refusal is not a strike) — or immediately on a refusal behind an orphan that has run longer than `Scripting:StuckOrphanQuarantineFactor` (default 10) × the timeout, which is what quarantines a never-returning `while(true)`. Both are mitigations; pre-emptive CPU/memory limits need an out-of-process runner (→ #750). **Stack:** unbounded recursion used to terminate the whole server — a `StackOverflowException` cannot be caught, and lmxopcua#779 reproduced it out of process (local function, mutual recursion, self-referencing `Func<>`, anonymous self-application, recursion through LINQ: the child process died with "Stack overflow." / SIGABRT). `ScriptEvaluator.Compile` now rewrites the script so the body and every lambda, anonymous method and local function starts with `ScriptStackGuard.Check()` (`RuntimeHelpers.TryEnsureSufficientExecutionStack`), so the recursion fails the script with `ScriptStackExhaustedException` — Bad quality and a script-log entry like any throwing script — while there is still stack left. A runtime check rather than an analyzer rule because recursion is not decidable from syntax (anonymous self-application never names itself); bounded recursion keeps working. Limits: the depth reached depends on the evaluating thread's stack size; a recursion that never re-enters script code is not seen (the sandbox exposes no such API); a script can catch the exception, which only unwinds it. Pinned by `ScriptRecursionContainmentTests` (one child process per shape) and `ScriptStackGuardInjectionTests`. Script authoring is gated by the AdminUI `ConfigEditor` policy — **`Administrator` or `Designer`**, not Administrator alone — and that same policy gates deploy, so a Designer can author a script and put it into production; that gate is the primary control (AdminUI-001 deliberately admitted Designers to the script pages and `/api/script-analysis/*`; lmxopcua#779 corrected this sentence, which used to say Admin-only). See `docs/ScriptEditor.md` §"Runtime safety".
+The sandbox cannot pre-empt a script. **Memory:** each run's own-thread allocation is sampled (`GC.GetAllocatedBytesForCurrentThread`) and a run over `Scripting:MaxAllocBytesPerRun` (default 64 MB) quarantines the script — but the sample is taken after the run returns, so a script that allocates fast enough (`new byte[int.MaxValue]` in a loop) can still OOM the process first. **CPU:** a tight loop keeps its pool thread after the timeout fires; `ScriptRunGuard` bounds that to one orphan per script by refusing further runs while it spins (Bad `"previous evaluation still running"`) and quarantines after three consecutive timeouts (a refusal is not a strike) — or immediately on a refusal behind an orphan that has run longer than `Scripting:StuckOrphanQuarantineFactor` (default 10) × the timeout, which is what quarantines a never-returning `while(true)`. Both are mitigations; pre-emptive CPU/memory limits need the out-of-process runner (→ #750 design, #780; opt-in via `Scripting:Runner=OutOfProcess`, below). **Stack:** unbounded recursion used to terminate the whole server — a `StackOverflowException` cannot be caught, and lmxopcua#779 reproduced it out of process (local function, mutual recursion, self-referencing `Func<>`, anonymous self-application, recursion through LINQ: the child process died with "Stack overflow." / SIGABRT). `ScriptEvaluator.Compile` now rewrites the script so the body and every lambda, anonymous method and local function starts with `ScriptStackGuard.Check()` (`RuntimeHelpers.TryEnsureSufficientExecutionStack`), so the recursion fails the script with `ScriptStackExhaustedException` — Bad quality and a script-log entry like any throwing script — while there is still stack left. A runtime check rather than an analyzer rule because recursion is not decidable from syntax (anonymous self-application never names itself); bounded recursion keeps working. Limits: the depth reached depends on the evaluating thread's stack size; a recursion that never re-enters script code is not seen (the sandbox exposes no such API); a script can catch the exception, which only unwinds it. Pinned by `ScriptRecursionContainmentTests` (one child process per shape) and `ScriptStackGuardInjectionTests`. Script authoring is gated by the AdminUI `ConfigEditor` policy — **`Administrator` or `Designer`**, not Administrator alone — and that same policy gates deploy, so a Designer can author a script and put it into production; that gate is the primary control (AdminUI-001 deliberately admitted Designers to the script pages and `/api/script-analysis/*`; lmxopcua#779 corrected this sentence, which used to say Admin-only). See `docs/ScriptEditor.md` §"Runtime safety".
 
 `System.Threading.Tasks` is denied (Core.Scripting-003), which prevents `Task.Run` / `Parallel` fan-out that would spawn background work outliving the timeout.
 
 
+#### Out-of-process runner (`Scripting:Runner`, lmxopcua#780)
+
+`Scripting:Runner` selects where compiled scripts run: **`InProcess`** (the default and the rollback — everything
+above, unchanged), **`OutOfProcess`**, or `Shadow` (design P2; not implemented yet, so it runs `InProcess` with a
+startup Warning). `Scripting:Runner:Seams` narrows `OutOfProcess` to a subset (`VirtualTag`, `Calculation`; the
+`ScriptedAlarm` seam stays in process for now — alarms go last, design §14 #10). Under `OutOfProcess` the virtual-tag
+and Calculation evaluators hand each compiled run to `OutOfProcessScriptRunner`
+(`Core.Scripting.OutOfProcess`), which runs it in a pool of `ZB.MOM.WW.OtOpcUa.ScriptWorker` processes:
+
+- **K shards** (`Scripting:Worker:Shards`, default 2) placed by a stable FNV-1a hash of the key, plus an on-demand
+  **isolation worker** that runs suspects one at a time. No worker starts until the first compiled evaluation, so a
+  node without scripts never launches one. The passthrough fast path never leaves the host.
+- **Two deadlines.** At the soft deadline `T` (the seam's budget, unchanged) the caller gets today's
+  `script timed out after …` failure and the run token is cancelled inside the worker; at `T + G`
+  (`Scripting:Worker:HardGrace`, default `max(1 s, T)`) the worker is **killed** (`Process.Kill(entireProcessTree)`,
+  plus a worker-side fail-fast watchdog) — the thread, its memory and its ALC go with it.
+- **Attribution and quarantine** live in the host and survive restarts: a deadline kill strikes exactly its key
+  (other evaluations in flight are victims, not strikes); a crash with no deadline crossed makes every key in flight
+  a suspect that must complete `Scripting:Worker:IsolationProbationRuns` (20) clean runs in the isolation worker,
+  where a crash strikes exactly one key. `Scripting:Worker:QuarantineAfterKills` (2) strikes within an hour, or the
+  existing consecutive-timeout and allocation rules, quarantine with the usual `"script quarantined: "` prefix; a
+  source change or a redeploy lifts it.
+- **Status codes.** Script faults keep `BadInternalError`. When the runner, not the script, failed — the worker
+  restarted under the run (`"script worker restarted"`) or no worker became ready within
+  `Scripting:Worker:UnavailableGrace` (5 s, `"script runner unavailable"`) — the tag publishes
+  **`BadResourceUnavailable` (0x80040000)** with its last value. This is ScadaBridge-visible (ScadaBridge#112).
+  The runner **fails closed**: no worker means Bad, never an in-process run.
+- **Containment.** The worker gets a cleared, allow-listed environment (no `ServerHistorian__ApiKey`, no
+  connection strings), an empty temp working directory, `DOTNET_GCHeapHardLimit = Scripting:Worker:HeapLimitBytes`
+  (512 MiB), a Windows Job Object (kill-on-close, one process, a commit backstop), a random current-user-only pipe
+  with a launch nonce in its environment, and no Akka / gRPC assemblies in its folder. It exits on pipe end of stream
+  or when its parent pid disappears. Results cross as protobuf `Variant`s carrying the exact CLR type, so
+  `(short)ctx.GetTag(x).Value` behaves as in process; an input or result type with no tag (a `List<T>`, a `Guid`)
+  is an explicit `unsupported type: …` failure rather than a conversion — a behaviour change from in process.
+- **Deployment.** The Host build copies the worker into `script-worker/` beside `OtOpcUa.Host.dll`
+  (`ScriptWorker.Deploy.targets`, Build and Publish); `Scripting:Worker:ExecutablePath` overrides it. It is run through
+  the dotnet muxer, so it needs a framework-dependent host (the docker-dev image). Not yet done (lmxopcua#780 P1
+  remainder): the PE cache (`Scripting:Worker:PeCacheDir` is validated — absolute, outside the content root — but not
+  used, so a worker restart recompiles), a self-contained worker for the Windows installs, the low-privilege worker
+  account and firewall rule, the runner-state gauge / readiness component, and the scripted-alarm seam.
+
+Pinned by `tests/Server/ZB.MOM.WW.OtOpcUa.ScriptWorker.Tests` (`Category=ScriptWorker`: real worker processes).
+
 #### Quarantine: what a client sees (status code)
 
 A quarantined script's output reads **`BadInternalError`** on OPC UA, the same code as a script that

docs/plans/2026-11-09-out-of-process-script-runner-design.md

@@ -665,6 +665,18 @@ per-shard state, restarts in the last hour and the quarantine list. Quarantines
    - Default stays `InProcess`. Enable on the docker-dev rig only.
    - Gate: §13 runaway / containment tests green on Linux (docker-dev) **and** Windows (windev box, which has
      the .NET 10 toolchain).
+   - **Partly landed in lmxopcua#780 (P1 slice):** `Scripting:Runner` / `Scripting:Runner:Seams` / `Scripting:Worker:*`
+     (bound, clamped, `PeCacheDir` path rule fail-closed), `IScriptRunner` + `InProcessScriptRunner`, the protobuf frame
+     protocol (`Core.Scripting.Protocol`), the `ScriptWorker` app (compile in the worker, P-thread scheduler, watchdog,
+     heartbeats, log forwarding, pipe-EOF / parent-pid exit, forbidden-assembly self-check), `OutOfProcessScriptRunner`
+     (K shards + isolation worker, soft/hard deadlines, attribution, kill-strike quarantine, backoff, fail closed,
+     Job Object on Windows), the VirtualTag and Calculation seams over it, and `BadResourceUnavailable` for
+     runner-unavailable / worker-restarted (ScadaBridge#112). The §13 containment cases run on macOS and Windows
+     (windev). Deviations: supervision is a plain object owned by DI, not `ScriptRunnerActor`/`ScriptWorkerActor`;
+     the per-seam batch submit (P0) is still one-at-a-time. Remaining: the HMAC'd PE cache, a self-contained worker
+     publish + the low-privilege account / pipe ACL / firewall rule (installer), the runner-state gauge and readiness
+     component, victim re-evaluation on shard return, isolation-worker idle stop, the orphan sweep by nonce file, the
+     scripted-alarm seam, the docker-dev enablement and the §8 perf harness.
 3. **P2, shadow mode on docker-dev and QA.**
    - `Shadow` runs the **in-process** evaluation as the published result, and *also* submits to the worker.
    - It compares value, status class and failure kind per evaluation, and counts

src/Core/ZB.MOM.WW.OtOpcUa.Commons/Engines/IVirtualTagEvaluator.cs

@@ -87,6 +87,19 @@ public sealed record VirtualTagEvalResult(bool Success, object? Value, string? R
     /// <param name="reason">Description of the failure cause.</param>
     /// <returns>A failed evaluation result.</returns>
     public static VirtualTagEvalResult Failure(string reason) => new(false, null, reason);
+
+    /// <summary>
+    ///     The OPC UA status a <see cref="Failure"/> publishes. Null (every failure the in-process path produces) means
+    ///     the seam's long-standing <c>BadInternalError</c>; the out-of-process runner sets
+    ///     <see cref="OpcUa.OpcUaStatus.BadResourceUnavailable"/> when the runner, not the script, failed (lmxopcua#780).
+    /// </summary>
+    public uint? StatusCode { get; init; }
+
+    /// <summary>A failure that is the runner's, not the script's: published <c>BadResourceUnavailable</c>.</summary>
+    /// <param name="reason">Description of the failure cause.</param>
+    /// <returns>A failed evaluation result carrying <see cref="OpcUa.OpcUaStatus.BadResourceUnavailable"/>.</returns>
+    public static VirtualTagEvalResult Unavailable(string reason) =>
+        new(false, null, reason) { StatusCode = OpcUa.OpcUaStatus.BadResourceUnavailable };
 }
 
 /// <summary>

src/Core/ZB.MOM.WW.OtOpcUa.Commons/OpcUa/OpcUaStatus.cs

@@ -47,6 +47,12 @@ public static class OpcUaStatus
     /// see docs/VirtualTags.md §"Quarantine: what a client sees").</summary>
     public const uint BadInternalError = 0x80020000;
 
+    /// <summary>The operating system / runtime could not provide a resource. The out-of-process script runner's code
+    /// for "the script did not run and it is not the script's fault" — its worker restarted under it, or no worker
+    /// was ready in time (lmxopcua#780, design §9). Distinct from <see cref="BadInternalError"/> so an operator, and
+    /// ScadaBridge, can tell a sick node from a broken script. Only produced under <c>Scripting:Runner=OutOfProcess</c>.</summary>
+    public const uint BadResourceUnavailable = 0x80040000;
+
     /// <summary>Part 4 severity bucket of <paramref name="statusCode"/>: the top two bits.</summary>
     /// <param name="statusCode">The status code to classify.</param>
     /// <returns>0 for Good, 1 for Uncertain, 2 or 3 for Bad.</returns>

src/Core/ZB.MOM.WW.OtOpcUa.Core.Scripting.OutOfProcess/OutOfProcessScriptRunner.cs

@@ -0,0 +1,505 @@
+using System.Collections.Concurrent;
+using System.Security.Cryptography;
+using System.Text;
+using Serilog;
+using Serilog.Core;
+using Serilog.Events;
+using ZB.MOM.WW.OtOpcUa.Commons.Engines;
+using ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol;
+using ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol.V1;
+
+namespace ZB.MOM.WW.OtOpcUa.Core.Scripting.OutOfProcess;
+
+/// <summary>
+///     The pre-emptible <see cref="IScriptRunner"/> (lmxopcua#780, design §3–§9): compiled scripts run in a pool of
+///     <c>ScriptWorker</c> processes — K shards placed by a stable hash of the script key, plus an isolation worker
+///     for suspects — so a script that overruns its hard deadline is stopped by killing its worker, and an OOM, a
+///     native crash or a fail-fast takes down a worker instead of the server.
+/// </summary>
+/// <remarks>
+///     <list type="bullet">
+///         <item><b>Two deadlines.</b> At the soft deadline <c>T</c> the caller gets today's timeout failure (and the
+///         run token is cancelled inside the worker). At <c>T + G</c> (<see cref="ScriptWorkerOptions.EffectiveHardGrace"/>)
+///         the worker is killed and the key takes a kill strike.</item>
+///         <item><b>Attribution.</b> A deadline kill blames exactly one key; the other evaluations in flight on that
+///         worker are victims and report <see cref="ScriptRunOutcome.WorkerRestartedReason"/> (no strike). A crash with
+///         no deadline crossed makes every key in flight a suspect, and suspects run in the isolation worker one at a
+///         time, where a crash names exactly one key. A suspect returns to its shard after
+///         <see cref="ScriptWorkerOptions.IsolationProbationRuns"/> clean runs.</item>
+///         <item><b>Quarantine</b> lives here, in the host, so it survives worker restarts: kill strikes (within an
+///         hour), consecutive soft timeouts, or one allocation-budget breach. Reasons keep the
+///         <see cref="ScriptRunGuard.QuarantinedReasonPrefix"/>, and a source change or <see cref="Reset"/> lifts them.</item>
+///         <item><b>Fail closed.</b> When no worker is ready within <see cref="ScriptWorkerOptions.UnavailableGrace"/>
+///         the result is <see cref="ScriptRunStatus.Unavailable"/> — never an in-process run.</item>
+///     </list>
+/// </remarks>
+public sealed class OutOfProcessScriptRunner : IScriptRunner, IAsyncDisposable, IDisposable
+{
+    /// <summary>The worker entry assembly's file name.</summary>
+    public const string WorkerAssemblyFileName = "ZB.MOM.WW.OtOpcUa.ScriptWorker.dll";
+
+    /// <summary>The folder under the host's base directory the Host build places the worker in.</summary>
+    public const string WorkerFolderName = "script-worker";
+
+    /// <summary>Failure reason when the worker could not take more work.</summary>
+    public const string WorkerBusyReason = "script worker busy";
+
+    private static readonly TimeSpan KillStrikeWindow = TimeSpan.FromHours(1);
+
+    private readonly ScriptingOptions _options;
+    private readonly ScriptWorkerOptions _worker;
+    private readonly ILogger _log;
+    private readonly ILogger _scriptRoot;
+    private readonly WorkerShard[] _shards;
+    private readonly WorkerShard _isolation;
+    private readonly ConcurrentDictionary<string, KeyState> _keys = new(StringComparer.Ordinal);
+    private readonly ConcurrentDictionary<string, string> _compileFailures = new(StringComparer.Ordinal);
+    private int _disposed;
+
+    /// <summary>Initializes the runner. No process starts until the first evaluation.</summary>
+    /// <param name="options">The node's <c>Scripting</c> options (sanitized again here).</param>
+    /// <param name="log">Host diagnostics: starts, kills, quarantines; null ⇒ Serilog's global logger.</param>
+    /// <param name="scriptRoot">Fallback logger for forwarded <c>ctx.Logger</c> lines; null ⇒ <paramref name="log"/>.</param>
+    public OutOfProcessScriptRunner(ScriptingOptions options, ILogger? log = null, ILogger? scriptRoot = null)
+        : this(options, log, scriptRoot, heartbeatInterval: TimeSpan.FromSeconds(1), loadTimeout: TimeSpan.FromSeconds(60))
+    {
+    }
+
+    internal OutOfProcessScriptRunner(ScriptingOptions options, ILogger? log, ILogger? scriptRoot,
+        TimeSpan heartbeatInterval, TimeSpan loadTimeout)
+    {
+        ArgumentNullException.ThrowIfNull(options);
+        _options = options.Sanitized(out _);
+        _worker = _options.Worker;
+        _log = log ?? Log.Logger;
+        _scriptRoot = scriptRoot ?? _log;
+        LoadTimeout = loadTimeout;
+        WorkerPath = ResolveWorkerPath(_worker);
+
+        var evalThreads = Math.Max(2, Environment.ProcessorCount / _worker.Shards);
+        _shards = new WorkerShard[_worker.Shards];
+        for (var i = 0; i < _shards.Length; i++)
+        {
+            var label = i.ToString(System.Globalization.CultureInfo.InvariantCulture);
+            _shards[i] = NewShard(label, isolation: false, evalThreads, heartbeatInterval);
+        }
+        _isolation = NewShard("iso", isolation: true, evalThreads: 1, heartbeatInterval);
+    }
+
+    /// <summary>The worker entry assembly this runner launches.</summary>
+    public string WorkerPath { get; }
+
+    /// <summary>How long a compile in the worker may take before the worker is killed.</summary>
+    internal TimeSpan LoadTimeout { get; }
+
+    /// <summary>The shard workers (tests).</summary>
+    internal IReadOnlyList<WorkerShard> Shards => _shards;
+
+    /// <summary>The isolation worker (tests).</summary>
+    internal WorkerShard Isolation => _isolation;
+
+    /// <summary>Scoped keys currently treated as suspects (tests / diagnostics).</summary>
+    internal IReadOnlyCollection<string> SuspectKeys =>
+        _keys.Where(kv => kv.Value.Suspect).Select(kv => kv.Key).ToArray();
+
+    /// <summary>The shard a key is placed on when it is not a suspect: a stable FNV-1a hash, so placement survives restarts.</summary>
+    /// <param name="scopedKey">The scoped key.</param>
+    /// <param name="shardCount">K.</param>
+    /// <returns>The shard index.</returns>
+    internal static int ShardIndex(string scopedKey, int shardCount)
+    {
+        var hash = 2166136261u;
+        foreach (var b in Encoding.UTF8.GetBytes(scopedKey))
+        {
+            hash ^= b;
+            hash *= 16777619u;
+        }
+        return (int)(hash % (uint)shardCount);
+    }
+
+    /// <summary>The default worker path, or the configured one.</summary>
+    /// <param name="worker">The worker options.</param>
+    /// <returns>The absolute worker path.</returns>
+    public static string ResolveWorkerPath(ScriptWorkerOptions worker)
+        => string.IsNullOrWhiteSpace(worker.ExecutablePath)
+            ? Path.Combine(AppContext.BaseDirectory, WorkerFolderName, WorkerAssemblyFileName)
+            : Path.GetFullPath(worker.ExecutablePath);
+
+    /// <inheritdoc />
+    public async Task<ScriptRunOutcome> RunAsync(ScriptInvocation invocation, CancellationToken ct = default)
+    {
+        ArgumentNullException.ThrowIfNull(invocation);
+        if (Volatile.Read(ref _disposed) != 0) return ScriptRunOutcome.Unavailable(ScriptRunOutcome.RunnerUnavailableReason);
+
+        var key = InProcessScriptRunner.ScopedKey(invocation.Kind, invocation.Key);
+        var state = Admit(key, invocation.Source);
+        if (state.QuarantineReason is { } quarantined) return ScriptRunOutcome.Failed(quarantined);
+
+        var sha = SHA256.HashData(Encoding.UTF8.GetBytes(invocation.Source));
+        var failureKey = InProcessScriptRunner.ScopedKey(invocation.Kind, Convert.ToHexString(sha));
+        if (_compileFailures.TryGetValue(failureKey, out var knownFailure)) return ScriptRunOutcome.Failed(knownFailure);
+
+        if (Interlocked.CompareExchange(ref state.InFlight, 1, 0) != 0)
+        {
+            ScriptRunGuard.RefusedCounter.Add(1, new KeyValuePair<string, object?>("script", key));
+            return ScriptRunOutcome.Failed(ScriptRunGuard.PreviousRunStillRunningReason);
+        }
+
+        var handedOff = false;
+        SemaphoreSlim? gate = null;
+        try
+        {
+            state.ScriptLogger = invocation.ScriptLogger;
+            var shard = state.Suspect ? _isolation : _shards[ShardIndex(key, _shards.Length)];
+            if (shard.IsolationGate is { } isolationGate)
+            {
+                if (!await isolationGate.WaitAsync(_worker.UnavailableGrace, ct).ConfigureAwait(false))
+                    return ScriptRunOutcome.Unavailable(ScriptRunOutcome.RunnerUnavailableReason);
+                gate = isolationGate;
+            }
+
+            var connection = await shard.GetReadyAsync(_worker.UnavailableGrace, ct).ConfigureAwait(false);
+            if (connection is null) return ScriptRunOutcome.Unavailable(ScriptRunOutcome.RunnerUnavailableReason);
+
+            var paths = invocation.Inputs.Keys.Order(StringComparer.Ordinal).ToArray();
+            WorkerConnection.LoadEntry? entry;
+            try
+            {
+                entry = await connection
+                    .EnsureLoadedAsync(key, WorkerShard.ToWire(invocation.Kind), invocation.Source, sha, paths)
+                    .WaitAsync(LoadTimeout, ct).ConfigureAwait(false);
+            }
+            catch (TimeoutException)
+            {
+                // A compile that never finishes is the script's fault (a pathological source): the worker dies, the
+                // key takes a kill strike through the exit handler.
+                _log.Warning("Script {ScriptKey}: compile in ScriptWorker[{Shard}] exceeded {Timeout} s; killing the worker",
+                    key, shard.Label, LoadTimeout.TotalSeconds);
+                connection.Kill(WorkerExitReason.KilledLoadTimeout, key);
+                return ScriptRunOutcome.Failed($"compile failure: compile did not finish within {LoadTimeout.TotalSeconds:F0} s");
+            }
+            if (entry?.Outcome is not { } outcome) return ScriptRunOutcome.Unavailable(ScriptRunOutcome.WorkerRestartedReason);
+            if (!outcome.Ok)
+            {
+                var reason = outcome.Error?.Kind switch
+                {
+                    ScriptError.Types.Kind.Compile => $"compile error: {outcome.Error.Message}",
+                    ScriptError.Types.Kind.Sandbox => $"sandbox violation: {outcome.Error.Message}",
+                    _ => $"compile failure: {outcome.Error?.Message}",
+                };
+                // Remembered until the next deploy boundary, so a broken script never re-enters Roslyn (design §7).
+                _compileFailures.TryAdd(failureKey, reason);
+                return ScriptRunOutcome.Failed(reason);
+            }
+
+            var pending = connection.Submit(key, BuildRequest(key, entry, invocation));
+            ArmHardDeadline(connection, pending, invocation.Timeout + _worker.EffectiveHardGrace(invocation.Timeout));
+
+            // From here the in-flight slot (and the isolation gate) belong to the evaluation itself: they are released
+            // when the worker answers or dies — not when this caller stops waiting at the soft deadline. That keeps a
+            // key single-flight between T and T + G, and the isolation worker strictly one-at-a-time.
+            handedOff = true;
+            var heldGate = gate;
+            _ = pending.Completion.ContinueWith(_ =>
+            {
+                Interlocked.Exchange(ref state.InFlight, 0);
+                heldGate?.Release();
+            }, CancellationToken.None, TaskContinuationOptions.ExecuteSynchronously, TaskScheduler.Default);
+
+            EvalResult? result;
+            try
+            {
+                result = await pending.Completion.WaitAsync(invocation.Timeout, ct).ConfigureAwait(false);
+            }
+            catch (TimeoutException)
+            {
+                // As in process: the run token is cancelled only once the caller has its timeout, so a polling script
+                // ends itself (and frees its slot) without the worker being killed.
+                connection.Cancel(pending);
+                if (ct.IsCancellationRequested) return ScriptRunOutcome.Failed("evaluation cancelled");
+                if (NoteTimeout(key, state, invocation.Timeout)) return ScriptRunOutcome.Failed(state.QuarantineReason!);
+                return ScriptRunOutcome.Failed($"{ScriptEvalFailureReasons.TimedOutPrefix}{invocation.Timeout.TotalSeconds:F1}s");
+            }
+
+            if (result is null) return ScriptRunOutcome.Unavailable(ScriptRunOutcome.WorkerRestartedReason);
+            return Complete(key, state, result);
+        }
+        catch (OperationCanceledException) when (ct.IsCancellationRequested)
+        {
+            return ScriptRunOutcome.Failed("evaluation cancelled");
+        }
+        finally
+        {
+            if (!handedOff)
+            {
+                Interlocked.Exchange(ref state.InFlight, 0);
+                gate?.Release();
+            }
+        }
+    }
+
+    /// <inheritdoc />
+    public void Reset(ScriptContextKind kind)
+    {
+        var prefix = InProcessScriptRunner.ScopedKey(kind, string.Empty);
+        var dropped = new List<string>();
+        foreach (var key in _keys.Keys)
+        {
+            if (key.StartsWith(prefix, StringComparison.Ordinal) && _keys.TryRemove(key, out _)) dropped.Add(key);
+        }
+        foreach (var key in _compileFailures.Keys)
+        {
+            if (key.StartsWith(prefix, StringComparison.Ordinal)) _compileFailures.TryRemove(key, out _);
+        }
+        foreach (var shard in _shards.Append(_isolation))
+            shard.Current?.Unload(dropped);
+    }
+
+    /// <inheritdoc />
+    public IReadOnlyCollection<string> QuarantinedKeys(ScriptContextKind kind)
+    {
+        var prefix = InProcessScriptRunner.ScopedKey(kind, string.Empty);
+        return _keys
+            .Where(kv => kv.Value.QuarantineReason is not null && kv.Key.StartsWith(prefix, StringComparison.Ordinal))
+            .Select(kv => kv.Key[prefix.Length..])
+            .ToArray();
+    }
+
+    /// <summary>Stops every worker.</summary>
+    /// <returns>A task that completes when they have ended.</returns>
+    public async ValueTask DisposeAsync()
+    {
+        if (Interlocked.Exchange(ref _disposed, 1) != 0) return;
+        await Task.WhenAll(_shards.Append(_isolation).Select(s => s.DisposeAsync().AsTask())).ConfigureAwait(false);
+    }
+
+    /// <summary>Stops every worker (blocking).</summary>
+    public void Dispose() => DisposeAsync().AsTask().GetAwaiter().GetResult();
+
+    private WorkerShard NewShard(string label, bool isolation, int evalThreads, TimeSpan heartbeatInterval)
+    {
+        var spec = new WorkerLaunchSpec(
+            Shard: label,
+            WorkerPath: WorkerPath,
+            HeapLimitBytes: _worker.HeapLimitBytes,
+            EvalThreads: evalThreads,
+            HardGrace: _worker.HardGrace ?? TimeSpan.FromSeconds(Math.Max(1, _options.RunTimeout.TotalSeconds)),
+            HeartbeatInterval: heartbeatInterval,
+            HandshakeTimeout: TimeSpan.FromSeconds(15));
+        return new WorkerShard(label, isolation,
+            ct => WorkerConnection.StartAsync(spec, _log, OnLogs, ct),
+            OnWorkerExit, _log);
+    }
+
+    private KeyState Admit(string key, string source)
+    {
+        while (true)
+        {
+            var state = _keys.GetOrAdd(key, static (_, src) => new KeyState(src), source);
+            if (string.Equals(state.Source, source, StringComparison.Ordinal)) return state;
+            // The script changed under this key: a clean slate, exactly as the in-process guard does. An evaluation
+            // of the old source still in flight releases the OLD state's slot when it ends.
+            if (_keys.TryUpdate(key, new KeyState(source), state)) continue;
+        }
+    }
+
+    private EvalRequest BuildRequest(string key, WorkerConnection.LoadEntry entry, ScriptInvocation invocation)
+    {
+        var request = new EvalRequest
+        {
+            Key = key,
+            NowUtcTicks = DateTime.UtcNow.Ticks,
+            SoftTimeoutMs = (uint)Math.Clamp(invocation.Timeout.TotalMilliseconds, 1, uint.MaxValue),
+            HardGraceMs = (uint)Math.Clamp(_worker.EffectiveHardGrace(invocation.Timeout).TotalMilliseconds, 1, uint.MaxValue),
+        };
+        foreach (var (path, snapshot) in invocation.Inputs)
+        {
+            if (snapshot is null) continue;
+            var input = new Input
+            {
+                StatusCode = snapshot.StatusCode,
+                SourceTsTicks = snapshot.SourceTimestampUtc is { } source ? VariantCodec.ToUtc(source).Ticks : 0,
+                ServerTsTicks = VariantCodec.ToUtc(snapshot.ServerTimestampUtc).Ticks,
+            };
+            if (entry.Slots.TryGetValue(path, out var slot)) input.Slot = slot;
+            else input.Path = path;
+            if (VariantCodec.TryEncode(snapshot.Value, out var variant, out var unsupported))
+            {
+                input.Value = variant;
+            }
+            else
+            {
+                // Never silently converted (design §14 #11): the worker answers UNSUPPORTED_TYPE for this input.
+                input.Unsupported = true;
+                input.UnsupportedType = unsupported ?? "?";
+            }
+            request.Inputs.Add(input);
+        }
+        return request;
+    }
+
+    private void ArmHardDeadline(WorkerConnection connection, PendingEval pending, TimeSpan after)
+    {
+        var cts = new CancellationTokenSource(after);
+        var registration = cts.Token.Register(() =>
+        {
+            if (pending.Completion.IsCompleted) return;
+            _log.Warning("Script {ScriptKey} exceeded its hard deadline ({Deadline} ms); killing ScriptWorker[{Shard}] pid {Pid}",
+                pending.Key, (long)after.TotalMilliseconds, connection.Shard, connection.Pid);
+            connection.Kill(WorkerExitReason.KilledDeadline, pending.Key);
+        });
+        _ = pending.Completion.ContinueWith(_ =>
+        {
+            registration.Dispose();
+            cts.Dispose();
+        }, CancellationToken.None, TaskContinuationOptions.ExecuteSynchronously, TaskScheduler.Default);
+    }
+
+    private ScriptRunOutcome Complete(string key, KeyState state, EvalResult result)
+    {
+        // The script returned control (a value or a throw): the soft-timeout streak resets, as in process.
+        Interlocked.Exchange(ref state.ConsecutiveTimeouts, 0);
+
+        if (_options.MaxAllocBytesPerRun > 0 && (long)result.AllocatedBytes > _options.MaxAllocBytesPerRun)
+        {
+            Quarantine(key, state,
+                $"one evaluation allocated {result.AllocatedBytes / (1024.0 * 1024.0):F1} MB, over the " +
+                $"{_options.MaxAllocBytesPerRun / (1024.0 * 1024.0):F0} MB budget (Scripting:MaxAllocBytesPerRun); " +
+                "the script is not evaluated again until its source changes or it is redeployed",
+                "allocation");
+            return ScriptRunOutcome.Failed(state.QuarantineReason!);
+        }
+
+        if (state.Suspect && Interlocked.Increment(ref state.ProbationRuns) >= _worker.IsolationProbationRuns)
+        {
+            state.Suspect = false;
+            _log.Information("Script {ScriptKey} completed {Runs} clean run(s) in the isolation worker; returning it to its shard",
+                key, _worker.IsolationProbationRuns);
+        }
+
+        switch (result.OutcomeCase)
+        {
+            case EvalResult.OutcomeOneofCase.Value:
+                try
+                {
+                    return ScriptRunOutcome.Ok(VariantCodec.Decode(result.Value));
+                }
+                catch (ScriptWorkerProtocolException ex)
+                {
+                    return ScriptRunOutcome.Failed($"script worker returned an undecodable value: {ex.Message}");
+                }
+            case EvalResult.OutcomeOneofCase.Predicate:
+                return ScriptRunOutcome.Ok(result.Predicate);
+            case EvalResult.OutcomeOneofCase.Error:
+                return result.Error.Kind switch
+                {
+                    ScriptError.Types.Kind.Threw => ScriptRunOutcome.Failed($"script threw: {result.Error.Message}"),
+                    ScriptError.Types.Kind.UnsupportedType => ScriptRunOutcome.Failed($"unsupported type: {result.Error.Message}"),
+                    ScriptError.Types.Kind.Busy => ScriptRunOutcome.Failed(WorkerBusyReason),
+                    ScriptError.Types.Kind.NotLoaded => ScriptRunOutcome.Unavailable(ScriptRunOutcome.WorkerRestartedReason),
+                    _ => ScriptRunOutcome.Failed($"script failed: {result.Error.Message}"),
+                };
+            default:
+                return ScriptRunOutcome.Ok(null);
+        }
+    }
+
+    private bool NoteTimeout(string key, KeyState state, TimeSpan timeout)
+    {
+        var count = Interlocked.Increment(ref state.ConsecutiveTimeouts);
+        if (count < _options.QuarantineAfterConsecutiveTimeouts) return false;
+        Quarantine(key, state,
+            $"{count} consecutive evaluation(s) timed out (budget {timeout.TotalMilliseconds:F0} ms); " +
+            "the script is not evaluated again until its source changes or it is redeployed",
+            "timeouts");
+        return true;
+    }
+
+    private void OnWorkerExit(WorkerShard shard, WorkerExit exit)
+    {
+        switch (exit.Reason)
+        {
+            case WorkerExitReason.KilledDeadline when exit.CulpritKey is { } culprit:
+                KillStrike(culprit, "it exceeded its hard deadline and its worker was killed", "killed");
+                break;
+            case WorkerExitReason.KilledLoadTimeout when exit.CulpritKey is { } culprit:
+                KillStrike(culprit, "its compile did not finish and its worker was killed", "killed");
+                break;
+            case WorkerExitReason.Crash or WorkerExitReason.KilledHeartbeat or WorkerExitReason.ProtocolFault:
+                if (shard.IsIsolation)
+                {
+                    // One evaluation at a time here: the crash is this key's (design §5.3.3).
+                    foreach (var key in exit.InFlightKeys)
+                        KillStrike(key, "it crashed the isolation worker", "isolated_crash");
+                }
+                else if (exit.InFlightKeys.Count > 0)
+                {
+                    foreach (var key in exit.InFlightKeys)
+                    {
+                        if (!_keys.TryGetValue(key, out var state)) continue;
+                        state.Suspect = true;
+                        Interlocked.Exchange(ref state.ProbationRuns, 0);
+                    }
+                    _log.Warning("ScriptWorker[{Shard}] ended ({Reason}) with no deadline crossed; {Count} script(s) in flight move to the isolation worker: {Suspects}",
+                        shard.Label, exit.Reason, exit.InFlightKeys.Count, string.Join(", ", exit.InFlightKeys));
+                }
+                break;
+        }
+    }
+
+    private void KillStrike(string key, string why, string metricReason)
+    {
+        if (!_keys.TryGetValue(key, out var state)) return;
+        int strikes;
+        lock (state.KillStrikes)
+        {
+            var now = DateTime.UtcNow;
+            state.KillStrikes.Add(now);
+            state.KillStrikes.RemoveAll(t => now - t > KillStrikeWindow);
+            strikes = state.KillStrikes.Count;
+        }
+        if (strikes >= _worker.QuarantineAfterKills)
+        {
+            Quarantine(key, state,
+                $"{why} ({strikes} time(s) in the last hour); the script is not evaluated again until its source changes or it is redeployed",
+                metricReason);
+        }
+    }
+
+    private void Quarantine(string key, KeyState state, string why, string metricReason)
+    {
+        var reason = ScriptRunGuard.QuarantinedReasonPrefix + why;
+        if (Interlocked.CompareExchange(ref state.QuarantineReason, reason, null) is not null) return;
+        ScriptRunGuard.QuarantinedCounter.Add(1,
+            new KeyValuePair<string, object?>("script", key),
+            new KeyValuePair<string, object?>("reason", metricReason));
+        _scriptRoot.ForContext(ScriptLoggerFactory.ScriptNameProperty, key).Error("Script {ScriptKey} quarantined: {Reason}", key, why);
+    }
+
+    private void OnLogs(LogBatch batch)
+    {
+        foreach (var line in batch.Lines)
+        {
+            var logger = _keys.TryGetValue(line.Key, out var state) && state.ScriptLogger is { } scoped ? scoped : _scriptRoot;
+            var level = line.Level <= (uint)LogEventLevel.Fatal ? (LogEventLevel)line.Level : LogEventLevel.Information;
+            if (string.IsNullOrEmpty(line.Exception))
+                logger.Write(level, "{ScriptMessage:l}", line.Rendered);
+            else
+                logger.Write(level, "{ScriptMessage:l}{NewLine}{ScriptException:l}", line.Rendered, Environment.NewLine, line.Exception);
+        }
+        if (batch.Dropped > 0)
+            _log.Warning("ScriptWorker dropped {Dropped} script log line(s): a script is logging faster than the pipe drains", batch.Dropped);
+    }
+
+    private sealed class KeyState(string source)
+    {
+        public readonly string Source = source;
+        public readonly List<DateTime> KillStrikes = [];
+        public int InFlight;
+        public int ConsecutiveTimeouts;
+        public int ProbationRuns;
+        public volatile bool Suspect;
+        public string? QuarantineReason;
+        public ILogger? ScriptLogger;
+    }
+}

src/Core/ZB.MOM.WW.OtOpcUa.Core.Scripting.OutOfProcess/WindowsJobObject.cs

@@ -0,0 +1,114 @@
+using System.ComponentModel;
+using System.Diagnostics;
+using System.Runtime.InteropServices;
+using System.Runtime.Versioning;
+using Microsoft.Win32.SafeHandles;
+
+namespace ZB.MOM.WW.OtOpcUa.Core.Scripting.OutOfProcess;
+
+/// <summary>
+///     A Windows Job Object holding one ScriptWorker (design §3.3, §5.2): <c>KILL_ON_JOB_CLOSE</c> so the kernel kills
+///     the worker when the host dies (its handle closes with it), <c>ACTIVE_PROCESS = 1</c> so the worker can start no
+///     child process, and a process-memory backstop slightly above the managed heap limit for native and JIT memory.
+/// </summary>
+[SupportedOSPlatform("windows")]
+internal sealed class WindowsJobObject : IDisposable
+{
+    private const int JobObjectExtendedLimitInformation = 9;
+    private const uint JOB_OBJECT_LIMIT_ACTIVE_PROCESS = 0x00000008;
+    private const uint JOB_OBJECT_LIMIT_PROCESS_MEMORY = 0x00000100;
+    private const uint JOB_OBJECT_LIMIT_DIE_ON_UNHANDLED_EXCEPTION = 0x00000400;
+    private const uint JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE = 0x00002000;
+
+    private readonly SafeFileHandle _handle;
+
+    private WindowsJobObject(SafeFileHandle handle) => _handle = handle;
+
+    /// <summary>Creates a job with the worker limits and assigns <paramref name="process"/> to it.</summary>
+    /// <param name="process">The freshly started worker.</param>
+    /// <param name="processMemoryLimitBytes">The per-process commit limit.</param>
+    /// <returns>The job; dispose it to kill the worker.</returns>
+    public static WindowsJobObject Assign(Process process, long processMemoryLimitBytes)
+    {
+        var handle = CreateJobObjectW(IntPtr.Zero, null);
+        if (handle.IsInvalid) throw new Win32Exception(Marshal.GetLastWin32Error(), "CreateJobObject failed");
+        var job = new WindowsJobObject(handle);
+        try
+        {
+            var info = new JOBOBJECT_EXTENDED_LIMIT_INFORMATION
+            {
+                BasicLimitInformation = new JOBOBJECT_BASIC_LIMIT_INFORMATION
+                {
+                    LimitFlags = JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE | JOB_OBJECT_LIMIT_ACTIVE_PROCESS
+                                 | JOB_OBJECT_LIMIT_PROCESS_MEMORY | JOB_OBJECT_LIMIT_DIE_ON_UNHANDLED_EXCEPTION,
+                    ActiveProcessLimit = 1,
+                },
+                ProcessMemoryLimit = (UIntPtr)(ulong)processMemoryLimitBytes,
+            };
+            if (!SetInformationJobObject(handle, JobObjectExtendedLimitInformation, ref info,
+                    (uint)Marshal.SizeOf<JOBOBJECT_EXTENDED_LIMIT_INFORMATION>()))
+                throw new Win32Exception(Marshal.GetLastWin32Error(), "SetInformationJobObject failed");
+            if (!AssignProcessToJobObject(handle, process.Handle))
+                throw new Win32Exception(Marshal.GetLastWin32Error(), "AssignProcessToJobObject failed");
+            return job;
+        }
+        catch
+        {
+            job.Dispose();
+            throw;
+        }
+    }
+
+    /// <summary>Closes the job handle, which kills every process still in it.</summary>
+    public void Dispose() => _handle.Dispose();
+
+    [StructLayout(LayoutKind.Sequential)]
+    private struct JOBOBJECT_BASIC_LIMIT_INFORMATION
+    {
+        public long PerProcessUserTimeLimit;
+        public long PerJobUserTimeLimit;
+        public uint LimitFlags;
+        public UIntPtr MinimumWorkingSetSize;
+        public UIntPtr MaximumWorkingSetSize;
+        public uint ActiveProcessLimit;
+        public UIntPtr Affinity;
+        public uint PriorityClass;
+        public uint SchedulingClass;
+    }
+
+    [StructLayout(LayoutKind.Sequential)]
+    private struct IO_COUNTERS
+    {
+        public ulong ReadOperationCount;
+        public ulong WriteOperationCount;
+        public ulong OtherOperationCount;
+        public ulong ReadTransferCount;
+        public ulong WriteTransferCount;
+        public ulong OtherTransferCount;
+    }
+
+    [StructLayout(LayoutKind.Sequential)]
+    private struct JOBOBJECT_EXTENDED_LIMIT_INFORMATION
+    {
+        public JOBOBJECT_BASIC_LIMIT_INFORMATION BasicLimitInformation;
+        public IO_COUNTERS IoInfo;
+        public UIntPtr ProcessMemoryLimit;
+        public UIntPtr JobMemoryLimit;
+        public UIntPtr PeakProcessMemoryUsed;
+        public UIntPtr PeakJobMemoryUsed;
+    }
+
+#pragma warning disable SYSLIB1054 // DllImport kept: LibraryImport would need AllowUnsafeBlocks for three calls.
+    [DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Unicode)]
+    private static extern SafeFileHandle CreateJobObjectW(IntPtr securityAttributes, string? name);
+
+    [DllImport("kernel32.dll", SetLastError = true)]
+    [return: MarshalAs(UnmanagedType.Bool)]
+    private static extern bool SetInformationJobObject(SafeFileHandle job, int infoClass,
+        ref JOBOBJECT_EXTENDED_LIMIT_INFORMATION info, uint length);
+
+    [DllImport("kernel32.dll", SetLastError = true)]
+    [return: MarshalAs(UnmanagedType.Bool)]
+    private static extern bool AssignProcessToJobObject(SafeFileHandle job, IntPtr process);
+#pragma warning restore SYSLIB1054
+}

src/Core/ZB.MOM.WW.OtOpcUa.Core.Scripting.OutOfProcess/WorkerConnection.cs

@@ -0,0 +1,699 @@
+using System.Collections.Concurrent;
+using System.Diagnostics;
+using System.IO.Pipes;
+using System.Security.Cryptography;
+using System.Text;
+using System.Threading.Channels;
+using Serilog;
+using ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol;
+using ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol.V1;
+
+namespace ZB.MOM.WW.OtOpcUa.Core.Scripting.OutOfProcess;
+
+/// <summary>How a worker process ended.</summary>
+internal enum WorkerExitReason
+{
+    /// <summary>It exited by itself with code 0 (a Shutdown).</summary>
+    Clean,
+
+    /// <summary>The host killed it: a script crossed its hard deadline (<see cref="WorkerExit.CulpritKey"/>).</summary>
+    KilledDeadline,
+
+    /// <summary>The host killed it: no frame for three heartbeat intervals.</summary>
+    KilledHeartbeat,
+
+    /// <summary>The host killed it: a compile did not finish in time (<see cref="WorkerExit.CulpritKey"/>).</summary>
+    KilledLoadTimeout,
+
+    /// <summary>It died by itself (OOM, heap limit, fail-fast, external kill).</summary>
+    Crash,
+
+    /// <summary>A framing or handshake violation.</summary>
+    ProtocolFault,
+
+    /// <summary>The runner is shutting down.</summary>
+    Disposed,
+}
+
+/// <summary>The end of one worker process.</summary>
+/// <param name="Reason">Why it ended.</param>
+/// <param name="CulpritKey">The scoped key the host blamed, for a deadline or load kill.</param>
+/// <param name="ExitCode">The OS exit code, when known.</param>
+/// <param name="InFlightKeys">The scoped keys that had an evaluation outstanding when it ended.</param>
+internal sealed record WorkerExit(WorkerExitReason Reason, string? CulpritKey, int? ExitCode, IReadOnlyList<string> InFlightKeys);
+
+/// <summary>What the host needs to launch one worker.</summary>
+/// <param name="Shard">The shard label (<c>0</c>, <c>1</c>, … or <c>iso</c>).</param>
+/// <param name="WorkerPath">The worker entry assembly (<c>.dll</c>, run through the dotnet muxer) or apphost.</param>
+/// <param name="HeapLimitBytes">The worker's <c>DOTNET_GCHeapHardLimit</c>.</param>
+/// <param name="EvalThreads">The worker scheduler's width (1 for the isolation worker).</param>
+/// <param name="HardGrace">The worker watchdog's grace past the soft deadline.</param>
+/// <param name="HeartbeatInterval">How often the worker sends a heartbeat.</param>
+/// <param name="HandshakeTimeout">How long a launch may take to reach Ready.</param>
+internal sealed record WorkerLaunchSpec(
+    string Shard,
+    string WorkerPath,
+    long HeapLimitBytes,
+    int EvalThreads,
+    TimeSpan HardGrace,
+    TimeSpan HeartbeatInterval,
+    TimeSpan HandshakeTimeout);
+
+/// <summary>
+///     One live ScriptWorker process and its pipe (lmxopcua#780, design §3–§6): launch with a cleared, allow-listed
+///     environment, a random pipe that accepts exactly one client, a nonce handshake, a frame reader and a coalescing
+///     writer, heartbeat supervision, and the kill. It never restarts itself; <see cref="WorkerShard"/> does that.
+/// </summary>
+internal sealed class WorkerConnection : IAsyncDisposable
+{
+    /// <summary>
+    ///     Environment variables a worker inherits from the host (design §6): the runtime's own knobs, the temp
+    ///     directories and the minimum a Windows process needs. Everything else — notably <c>ServerHistorian__ApiKey</c>,
+    ///     ConfigDb connection strings and every other <c>Section__Key</c> override — is dropped.
+    /// </summary>
+    internal static readonly IReadOnlyList<string> InheritedEnvironment =
+    [
+        "PATH", "TEMP", "TMP", "TMPDIR", "HOME", "SystemRoot", "SYSTEMROOT", "windir", "SystemDrive", "ComSpec",
+        "PATHEXT", "NUMBER_OF_PROCESSORS", "PROCESSOR_ARCHITECTURE", "LOCALAPPDATA",
+    ];
+
+    private readonly Process _process;
+    private readonly NamedPipeServerStream _pipe;
+    private readonly IDisposable? _job;
+    private readonly string _workDir;
+    private readonly ILogger _log;
+    private readonly Action<LogBatch> _onLogs;
+    private readonly Channel<Envelope> _outbound = Channel.CreateUnbounded<Envelope>(new UnboundedChannelOptions { SingleReader = true });
+    private readonly ConcurrentDictionary<ulong, PendingEval> _pending = new();
+    private readonly ConcurrentDictionary<ulong, TaskCompletionSource<LoadResult>> _loads = new();
+    private readonly ConcurrentDictionary<string, LoadEntry> _loaded = new(StringComparer.Ordinal);
+    private readonly TaskCompletionSource<WorkerExit> _exited = new(TaskCreationOptions.RunContinuationsAsynchronously);
+    private readonly CancellationTokenSource _stopping = new();
+    private readonly TimeSpan _heartbeatInterval;
+    private TaskCompletionSource<DiagnosticsReply>? _diag;
+    private (WorkerExitReason Reason, string? Culprit)? _killedFor;
+    private long _lastFrameTimestamp;
+    private long _seq;
+    private long _nextEvalId;
+    private long _nextLoadId;
+    private int _maxFrameBytes = ScriptWorkerFrameCodec.DefaultMaxFrameBytes;
+    private int _disposed;
+
+    private WorkerConnection(string shard, Process process, NamedPipeServerStream pipe, IDisposable? job, string workDir,
+        ILogger log, Action<LogBatch> onLogs, TimeSpan heartbeatInterval)
+    {
+        Shard = shard;
+        _process = process;
+        _pipe = pipe;
+        _job = job;
+        _workDir = workDir;
+        _log = log;
+        _onLogs = onLogs;
+        _heartbeatInterval = heartbeatInterval;
+        Pid = process.Id;
+    }
+
+    /// <summary>The shard label.</summary>
+    public string Shard { get; }
+
+    /// <summary>The worker's process id.</summary>
+    public int Pid { get; }
+
+    /// <summary>Completes when the worker has ended, with why.</summary>
+    public Task<WorkerExit> Exited => _exited.Task;
+
+    /// <summary>Whether the worker is still serving.</summary>
+    public bool IsAlive => !_exited.Task.IsCompleted && !_stopping.IsCancellationRequested;
+
+    /// <summary><see cref="Stopwatch.GetTimestamp"/> when the handshake completed.</summary>
+    public long ReadyTimestamp { get; private set; }
+
+    /// <summary>Evaluations currently outstanding on this worker.</summary>
+    public int InFlightCount => _pending.Count;
+
+    /// <summary>Launches a worker and completes the handshake.</summary>
+    /// <param name="spec">What to launch.</param>
+    /// <param name="log">Host diagnostics (stderr lines, exits).</param>
+    /// <param name="onLogs">Receives the worker's forwarded <c>ctx.Logger</c> batches.</param>
+    /// <param name="ct">Cancellation.</param>
+    /// <returns>A ready connection.</returns>
+    public static async Task<WorkerConnection> StartAsync(WorkerLaunchSpec spec, ILogger log, Action<LogBatch> onLogs, CancellationToken ct)
+    {
+        var pipeName = "otopcua-sw-" + Convert.ToHexString(RandomNumberGenerator.GetBytes(12)).ToLowerInvariant();
+        var nonce = Convert.ToHexString(RandomNumberGenerator.GetBytes(32));
+        var workDir = Path.Combine(Path.GetTempPath(), "otopcua-scriptworker", pipeName);
+        Directory.CreateDirectory(workDir);
+
+        // One instance, current user only: the pipe accepts exactly one connection, from this account.
+        var pipe = new NamedPipeServerStream(pipeName, PipeDirection.InOut, maxNumberOfServerInstances: 1,
+            PipeTransmissionMode.Byte, PipeOptions.Asynchronous | PipeOptions.CurrentUserOnly);
+        Process? process = null;
+        IDisposable? job = null;
+        try
+        {
+            var psi = BuildStartInfo(spec, pipeName, nonce, workDir);
+            process = new Process { StartInfo = psi, EnableRaisingEvents = true };
+            if (!process.Start()) throw new InvalidOperationException("the worker process did not start");
+            if (OperatingSystem.IsWindows())
+            {
+                // Native and JIT memory backstop above the managed heap limit.
+                job = WindowsJobObject.Assign(process, spec.HeapLimitBytes + 256L * 1024 * 1024);
+            }
+            var shardLabel = spec.Shard;
+            process.ErrorDataReceived += (_, e) =>
+            {
+                if (e.Data is { Length: > 0 } line) log.Warning("ScriptWorker[{Shard}] {WorkerStderr}", shardLabel, line);
+            };
+            process.OutputDataReceived += (_, e) =>
+            {
+                if (e.Data is { Length: > 0 } line) log.Debug("ScriptWorker[{Shard}] stdout {WorkerStdout}", shardLabel, line);
+            };
+            process.BeginErrorReadLine();
+            process.BeginOutputReadLine();
+
+            using var handshakeCts = CancellationTokenSource.CreateLinkedTokenSource(ct);
+            handshakeCts.CancelAfter(spec.HandshakeTimeout);
+            var exitedEarly = process.WaitForExitAsync(handshakeCts.Token);
+            var accept = pipe.WaitForConnectionAsync(handshakeCts.Token);
+            if (await Task.WhenAny(accept, exitedEarly).ConfigureAwait(false) != accept)
+                throw new InvalidOperationException(
+                    $"the worker exited (code {SafeExitCode(process)}) before connecting to its pipe");
+            await accept.ConfigureAwait(false);
+
+            var hello = new Hello
+            {
+                Nonce = nonce,
+                MaxFrameBytes = ScriptWorkerFrameCodec.DefaultMaxFrameBytes,
+                EvalThreads = (uint)spec.EvalThreads,
+                QueueCapacity = 4096,
+                HardGraceMs = (uint)Math.Clamp(spec.HardGrace.TotalMilliseconds, 1, uint.MaxValue),
+                HeartbeatIntervalMs = (uint)spec.HeartbeatInterval.TotalMilliseconds,
+                MaxLogLines = 1000,
+            };
+            await HandshakeAsync(pipe, hello, nonce, process.Id, handshakeCts.Token).ConfigureAwait(false);
+
+            var connection = new WorkerConnection(spec.Shard, process, pipe, job, workDir, log, onLogs, spec.HeartbeatInterval);
+            connection.Begin();
+            return connection;
+        }
+        catch
+        {
+            try { if (process is { HasExited: false }) process.Kill(entireProcessTree: true); } catch { /* best effort */ }
+            job?.Dispose();
+            process?.Dispose();
+            await pipe.DisposeAsync().ConfigureAwait(false);
+            TryDeleteDirectory(workDir);
+            throw;
+        }
+    }
+
+    /// <summary>
+    ///     The host half of the handshake: send <paramref name="hello"/>, require a <c>Ready</c> as the first frame,
+    ///     echoing <paramref name="expectedNonce"/> (constant-time compare) from <paramref name="expectedPid"/>.
+    /// </summary>
+    /// <param name="stream">The accepted pipe.</param>
+    /// <param name="hello">The Hello to send.</param>
+    /// <param name="expectedNonce">The nonce put in the worker's environment.</param>
+    /// <param name="expectedPid">The launched process id; null skips the check.</param>
+    /// <param name="ct">Cancellation (the handshake timeout).</param>
+    /// <returns>The worker's Ready.</returns>
+    /// <exception cref="ScriptWorkerProtocolException">Anything but a matching Ready.</exception>
+    internal static async Task<Ready> HandshakeAsync(Stream stream, Hello hello, string expectedNonce, int? expectedPid, CancellationToken ct)
+    {
+        await ScriptWorkerFrameCodec.WriteAsync(stream, new Envelope
+        {
+            ProtocolVersion = ScriptWorkerFrameCodec.ProtocolVersion,
+            Seq = 1,
+            Hello = hello,
+        }, ScriptWorkerFrameCodec.DefaultMaxFrameBytes, ct).ConfigureAwait(false);
+        await stream.FlushAsync(ct).ConfigureAwait(false);
+
+        var reply = await ScriptWorkerFrameCodec.ReadAsync(stream, ScriptWorkerFrameCodec.DefaultMaxFrameBytes, ct).ConfigureAwait(false)
+                    ?? throw new ScriptWorkerProtocolException("the worker closed the pipe during the handshake");
+        if (reply.BodyCase != Envelope.BodyOneofCase.Ready)
+            throw new ScriptWorkerProtocolException($"expected Ready, got {reply.BodyCase}");
+        var expected = Encoding.UTF8.GetBytes(expectedNonce);
+        var actual = Encoding.UTF8.GetBytes(reply.Ready.Nonce ?? string.Empty);
+        if (!CryptographicOperations.FixedTimeEquals(expected, actual))
+            throw new ScriptWorkerProtocolException("the worker's nonce does not match the launch nonce");
+        if (expectedPid is { } pid && reply.Ready.Pid != pid)
+            throw new ScriptWorkerProtocolException($"the pipe client reports pid {reply.Ready.Pid}, not the launched {pid}");
+        return reply.Ready;
+    }
+
+    private static ProcessStartInfo BuildStartInfo(WorkerLaunchSpec spec, string pipeName, string nonce, string workDir)
+    {
+        var psi = new ProcessStartInfo
+        {
+            UseShellExecute = false,
+            CreateNoWindow = true,
+            RedirectStandardError = true,
+            RedirectStandardOutput = true,
+            RedirectStandardInput = false,
+            WorkingDirectory = workDir,
+        };
+        if (spec.WorkerPath.EndsWith(".dll", StringComparison.OrdinalIgnoreCase))
+        {
+            psi.FileName = ResolveMuxer();
+            psi.ArgumentList.Add("exec");
+            psi.ArgumentList.Add(spec.WorkerPath);
+        }
+        else
+        {
+            psi.FileName = spec.WorkerPath;
+        }
+
+        // Cleared, then repopulated from an allow-list (design §6). ProcessStartInfo.Environment starts as a copy of
+        // the host's environment; ScadaBridge's sandbox inherits it whole, which this design rejects.
+        var inherited = psi.Environment.ToDictionary(kv => kv.Key, kv => kv.Value, StringComparer.Ordinal);
+        psi.Environment.Clear();
+        foreach (var (name, value) in inherited)
+        {
+            if (value is null) continue;
+            if (InheritedEnvironment.Contains(name, StringComparer.OrdinalIgnoreCase)
+                || (name.StartsWith("DOTNET_", StringComparison.OrdinalIgnoreCase)
+                    && !name.StartsWith("DOTNET_GCHeap", StringComparison.OrdinalIgnoreCase)))
+                psi.Environment[name] = value;
+        }
+        psi.Environment["DOTNET_GCHeapHardLimit"] = "0x" + spec.HeapLimitBytes.ToString("X", System.Globalization.CultureInfo.InvariantCulture);
+        psi.Environment["DOTNET_gcServer"] = "0";
+        psi.Environment["DOTNET_CLI_TELEMETRY_OPTOUT"] = "1";
+        psi.Environment[ScriptWorkerEnvironment.PipeName] = pipeName;
+        psi.Environment[ScriptWorkerEnvironment.Nonce] = nonce;
+        psi.Environment[ScriptWorkerEnvironment.ParentPid] = Environment.ProcessId.ToString(System.Globalization.CultureInfo.InvariantCulture);
+        psi.Environment[ScriptWorkerEnvironment.Shard] = spec.Shard;
+        return psi;
+    }
+
+    /// <summary>The dotnet muxer that runs a framework-dependent worker <c>.dll</c>.</summary>
+    /// <returns>The muxer path, or plain <c>dotnet</c> (resolved on PATH) as a last resort.</returns>
+    internal static string ResolveMuxer()
+    {
+        var hostPath = Environment.GetEnvironmentVariable("DOTNET_HOST_PATH");
+        if (!string.IsNullOrEmpty(hostPath) && File.Exists(hostPath)) return hostPath;
+        var processPath = Environment.ProcessPath;
+        if (processPath is not null
+            && string.Equals(Path.GetFileNameWithoutExtension(processPath), "dotnet", StringComparison.OrdinalIgnoreCase))
+            return processPath;
+        var root = Environment.GetEnvironmentVariable("DOTNET_ROOT");
+        if (!string.IsNullOrEmpty(root))
+        {
+            var candidate = Path.Combine(root, OperatingSystem.IsWindows() ? "dotnet.exe" : "dotnet");
+            if (File.Exists(candidate)) return candidate;
+        }
+        return "dotnet";
+    }
+
+    private void Begin()
+    {
+        ReadyTimestamp = Stopwatch.GetTimestamp();
+        Volatile.Write(ref _lastFrameTimestamp, ReadyTimestamp);
+        _ = Task.Run(ReadLoopAsync);
+        _ = Task.Run(WriteLoopAsync);
+        _ = Task.Run(HeartbeatMonitorAsync);
+        _ = Task.Run(WatchProcessAsync);
+    }
+
+    /// <summary>Ensures <paramref name="key"/> is compiled in this worker at <paramref name="sourceHash"/>.</summary>
+    /// <param name="key">The scoped key.</param>
+    /// <param name="kind">The context kind.</param>
+    /// <param name="source">The source.</param>
+    /// <param name="sourceHash">SHA-256 of the source.</param>
+    /// <param name="inputPaths">The slot order.</param>
+    /// <returns>The load outcome and the slot map; null when the worker ended first.</returns>
+    public Task<LoadEntry?> EnsureLoadedAsync(string key, ContextKind kind, string source, byte[] sourceHash, IReadOnlyList<string> inputPaths)
+    {
+        var hashHex = Convert.ToHexString(sourceHash);
+        if (_loaded.TryGetValue(key, out var existing) && existing.SourceHash == hashHex && existing.SameSlots(inputPaths))
+            return existing.Ready;
+
+        var entry = new LoadEntry(hashHex, inputPaths);
+        _loaded[key] = entry;
+        var loadId = (ulong)Interlocked.Increment(ref _nextLoadId);
+        var tcs = new TaskCompletionSource<LoadResult>(TaskCreationOptions.RunContinuationsAsynchronously);
+        _loads[loadId] = tcs;
+        var load = new LoadScripts { LoadId = loadId };
+        var script = new ScriptSource { Key = key, Kind = kind, Source = source, SourceSha256 = Google.Protobuf.ByteString.CopyFrom(sourceHash) };
+        script.InputPaths.AddRange(inputPaths);
+        load.Scripts.Add(script);
+        if (!Send(new Envelope { Load = load })) { _loads.TryRemove(loadId, out _); entry.Complete(null); return entry.Ready; }
+
+        _ = tcs.Task.ContinueWith(t =>
+        {
+            if (t.IsCompletedSuccessfully)
+            {
+                var outcome = t.Result.Outcomes.FirstOrDefault(o => o.Key == key);
+                entry.Complete(outcome ?? new LoadOutcome { Key = key, Ok = false, Error = new ScriptError { Kind = ScriptError.Types.Kind.Threw, Message = "no load outcome" } });
+                if (outcome is { Ok: false }) _loaded.TryRemove(new KeyValuePair<string, LoadEntry>(key, entry));
+            }
+            else
+            {
+                entry.Complete(null);
+                _loaded.TryRemove(new KeyValuePair<string, LoadEntry>(key, entry));
+            }
+        }, CancellationToken.None, TaskContinuationOptions.ExecuteSynchronously, TaskScheduler.Default);
+        return entry.Ready;
+    }
+
+    /// <summary>Forgets a key's compiled form here and in the worker.</summary>
+    /// <param name="keys">The scoped keys.</param>
+    public void Unload(IReadOnlyCollection<string> keys)
+    {
+        var unload = new Unload();
+        foreach (var key in keys)
+            if (_loaded.TryRemove(key, out _)) unload.Keys.Add(key);
+        if (unload.Keys.Count > 0) Send(new Envelope { Unload = unload });
+    }
+
+    /// <summary>Submits one evaluation. Its <see cref="PendingEval.Completion"/> yields null when the worker ends first.</summary>
+    /// <param name="key">The scoped key.</param>
+    /// <param name="request">The request (its id is assigned here).</param>
+    /// <returns>The pending evaluation.</returns>
+    public PendingEval Submit(string key, EvalRequest request)
+    {
+        request.EvalId = (ulong)Interlocked.Increment(ref _nextEvalId);
+        var pending = new PendingEval(key, request.EvalId);
+        _pending[request.EvalId] = pending;
+        var batch = new EvalBatch();
+        batch.Items.Add(request);
+        if (!Send(new Envelope { Eval = batch }) || _exited.Task.IsCompleted)
+        {
+            if (_pending.TryRemove(request.EvalId, out _)) pending.Complete(null);
+        }
+        return pending;
+    }
+
+    /// <summary>Cancels a run's <c>ctx.CancellationToken</c> in the worker (sent at the soft deadline).</summary>
+    /// <param name="pending">The evaluation.</param>
+    public void Cancel(PendingEval pending)
+    {
+        if (!pending.Completion.IsCompleted) Send(new Envelope { Cancel = new Protocol.V1.Cancel { EvalId = pending.EvalId } });
+    }
+
+    /// <summary>Asks the worker for its process diagnostics (loaded assemblies, environment names).</summary>
+    /// <param name="timeout">How long to wait.</param>
+    /// <returns>The reply.</returns>
+    public async Task<DiagnosticsReply> DiagnosticsAsync(TimeSpan timeout)
+    {
+        var tcs = new TaskCompletionSource<DiagnosticsReply>(TaskCreationOptions.RunContinuationsAsynchronously);
+        Interlocked.Exchange(ref _diag, tcs);
+        Send(new Envelope { DiagRequest = new DiagnosticsRequest() });
+        return await tcs.Task.WaitAsync(timeout).ConfigureAwait(false);
+    }
+
+    /// <summary>Kills the worker (process tree). The first reason given is the one recorded.</summary>
+    /// <param name="reason">Why.</param>
+    /// <param name="culpritKey">The scoped key blamed, if any.</param>
+    public void Kill(WorkerExitReason reason, string? culpritKey)
+    {
+        lock (_pending)
+        {
+            _killedFor ??= (reason, culpritKey);
+        }
+        try
+        {
+            if (!_process.HasExited) _process.Kill(entireProcessTree: true);
+        }
+        catch (InvalidOperationException) { /* already gone */ }
+        catch (System.ComponentModel.Win32Exception ex)
+        {
+            _log.Warning(ex, "ScriptWorker[{Shard}] kill of pid {Pid} failed", Shard, Pid);
+        }
+    }
+
+    /// <summary>Asks the worker to stop, waits briefly, then kills it.</summary>
+    /// <returns>A task that completes when the worker has ended.</returns>
+    public async ValueTask DisposeAsync()
+    {
+        // Both the shard (on exit) and the runner (on shutdown) dispose a connection; only the first does the work.
+        if (Interlocked.Exchange(ref _disposed, 1) != 0) return;
+        if (!_exited.Task.IsCompleted)
+        {
+            lock (_pending) { _killedFor ??= (WorkerExitReason.Disposed, null); }
+            Send(new Envelope { Shutdown = new Shutdown() });
+            try
+            {
+                await _process.WaitForExitAsync().WaitAsync(TimeSpan.FromSeconds(1)).ConfigureAwait(false);
+            }
+            catch (TimeoutException)
+            {
+                Kill(WorkerExitReason.Disposed, null);
+            }
+            try { await _exited.Task.WaitAsync(TimeSpan.FromSeconds(5)).ConfigureAwait(false); } catch (TimeoutException) { }
+        }
+        _stopping.Cancel();
+        _outbound.Writer.TryComplete();
+        await _pipe.DisposeAsync().ConfigureAwait(false);
+        _job?.Dispose();
+        _process.Dispose();
+        TryDeleteDirectory(_workDir);
+    }
+
+    /// <summary>Test hook: closes the host end of the pipe without touching the process, as a dying host would.</summary>
+    internal void SeverPipeForTest() => _pipe.Dispose();
+
+    private bool Send(Envelope envelope)
+    {
+        envelope.ProtocolVersion = ScriptWorkerFrameCodec.ProtocolVersion;
+        return _outbound.Writer.TryWrite(envelope);
+    }
+
+    private async Task WriteLoopAsync()
+    {
+        var reader = _outbound.Reader;
+        try
+        {
+            while (await reader.WaitToReadAsync(_stopping.Token).ConfigureAwait(false))
+            {
+                // Opportunistic batching (design §4.5): every evaluation queued right now goes out as ONE EvalBatch.
+                EvalBatch? batch = null;
+                while (reader.TryRead(out var envelope))
+                {
+                    if (envelope.BodyCase == Envelope.BodyOneofCase.Eval)
+                    {
+                        (batch ??= new EvalBatch()).Items.AddRange(envelope.Eval.Items);
+                        continue;
+                    }
+                    envelope.Seq = (ulong)Interlocked.Increment(ref _seq);
+                    await ScriptWorkerFrameCodec.WriteAsync(_pipe, envelope, _maxFrameBytes, _stopping.Token).ConfigureAwait(false);
+                }
+                if (batch is not null)
+                {
+                    await ScriptWorkerFrameCodec.WriteAsync(_pipe, new Envelope
+                    {
+                        ProtocolVersion = ScriptWorkerFrameCodec.ProtocolVersion,
+                        Seq = (ulong)Interlocked.Increment(ref _seq),
+                        Eval = batch,
+                    }, _maxFrameBytes, _stopping.Token).ConfigureAwait(false);
+                }
+                await _pipe.FlushAsync(_stopping.Token).ConfigureAwait(false);
+            }
+        }
+        catch (OperationCanceledException) { }
+        catch (Exception ex) when (ex is IOException or ObjectDisposedException or ScriptWorkerProtocolException)
+        {
+            if (!_stopping.IsCancellationRequested)
+                _log.Debug(ex, "ScriptWorker[{Shard}] pipe write ended", Shard);
+            Kill(WorkerExitReason.Crash, null);
+        }
+    }
+
+    private async Task ReadLoopAsync()
+    {
+        WorkerExitReason? fault = null;
+        try
+        {
+            while (true)
+            {
+                var frame = await ScriptWorkerFrameCodec.ReadAsync(_pipe, _maxFrameBytes, _stopping.Token).ConfigureAwait(false);
+                if (frame is null) break;
+                Volatile.Write(ref _lastFrameTimestamp, Stopwatch.GetTimestamp());
+                switch (frame.BodyCase)
+                {
+                    case Envelope.BodyOneofCase.Results:
+                        foreach (var result in frame.Results.Items)
+                        {
+                            // An eval id with no outstanding request is a protocol violation (design §6 "what the host
+                            // trusts"), except for one that was already completed by a kill race — ignored then.
+                            if (_pending.TryRemove(result.EvalId, out var pending)) pending.Complete(result);
+                            else if (result.EvalId == 0 || result.EvalId > (ulong)Interlocked.Read(ref _nextEvalId))
+                                throw new ScriptWorkerProtocolException($"result for unknown eval id {result.EvalId}");
+                        }
+                        break;
+                    case Envelope.BodyOneofCase.LoadResult:
+                        if (_loads.TryRemove(frame.LoadResult.LoadId, out var load)) load.TrySetResult(frame.LoadResult);
+                        else throw new ScriptWorkerProtocolException($"load result for unknown load id {frame.LoadResult.LoadId}");
+                        break;
+                    case Envelope.BodyOneofCase.Logs:
+                        try { _onLogs(frame.Logs); }
+                        catch (Exception ex) { _log.Warning(ex, "ScriptWorker[{Shard}] log forwarding threw", Shard); }
+                        break;
+                    case Envelope.BodyOneofCase.Heartbeat:
+                        break;
+                    case Envelope.BodyOneofCase.DiagReply:
+                        Volatile.Read(ref _diag)?.TrySetResult(frame.DiagReply);
+                        break;
+                    case Envelope.BodyOneofCase.Fault:
+                        _log.Warning("ScriptWorker[{Shard}] reported a fault: {Fault}", Shard, frame.Fault.Message);
+                        break;
+                    default:
+                        throw new ScriptWorkerProtocolException($"unexpected frame {frame.BodyCase} from the worker");
+                }
+            }
+        }
+        catch (OperationCanceledException) { }
+        catch (ScriptWorkerProtocolException ex)
+        {
+            _log.Warning("ScriptWorker[{Shard}] protocol violation: {Message}; killing pid {Pid}", Shard, ex.Message, Pid);
+            fault = WorkerExitReason.ProtocolFault;
+        }
+        catch (Exception ex) when (ex is IOException or ObjectDisposedException)
+        {
+        }
+
+        // The pipe is gone: the worker is dead or dying. Make sure, then report.
+        try
+        {
+            if (fault is { } f) Kill(f, null);
+            try
+            {
+                await _process.WaitForExitAsync().WaitAsync(TimeSpan.FromSeconds(2)).ConfigureAwait(false);
+            }
+            catch (TimeoutException)
+            {
+                Kill(WorkerExitReason.Crash, null);
+                try { await _process.WaitForExitAsync().WaitAsync(TimeSpan.FromSeconds(5)).ConfigureAwait(false); } catch (TimeoutException) { }
+            }
+        }
+        catch (InvalidOperationException)
+        {
+            // The process object was disposed by a concurrent shutdown: the worker is already gone.
+        }
+        Finish();
+    }
+
+    private async Task WatchProcessAsync()
+    {
+        try { await _process.WaitForExitAsync(_stopping.Token).ConfigureAwait(false); }
+        catch (OperationCanceledException) { return; }
+        catch (InvalidOperationException) { return; }
+        // The reader normally finishes first on EOF; this covers a worker that died while the pipe stayed open.
+        await Task.Delay(TimeSpan.FromSeconds(2)).ConfigureAwait(false);
+        Finish();
+    }
+
+    private async Task HeartbeatMonitorAsync()
+    {
+        using var timer = new PeriodicTimer(_heartbeatInterval);
+        try
+        {
+            while (await timer.WaitForNextTickAsync(_stopping.Token).ConfigureAwait(false))
+            {
+                if (_exited.Task.IsCompleted) return;
+                var silent = Stopwatch.GetElapsedTime(Volatile.Read(ref _lastFrameTimestamp));
+                if (silent > _heartbeatInterval * 3)
+                {
+                    _log.Warning("ScriptWorker[{Shard}] pid {Pid} sent nothing for {Silent} ms; killing it", Shard, Pid, (long)silent.TotalMilliseconds);
+                    Kill(WorkerExitReason.KilledHeartbeat, null);
+                    return;
+                }
+            }
+        }
+        catch (OperationCanceledException) { }
+    }
+
+    private void Finish()
+    {
+        int? code = null;
+        try { if (_process.HasExited) code = _process.ExitCode; } catch (InvalidOperationException) { }
+
+        (WorkerExitReason Reason, string? Culprit)? killed;
+        lock (_pending) { killed = _killedFor; }
+        var reason = killed?.Reason ?? (code == 0 ? WorkerExitReason.Clean : WorkerExitReason.Crash);
+        var inFlight = _pending.Values.Select(p => p.Key).Distinct(StringComparer.Ordinal).ToArray();
+        if (!_exited.TrySetResult(new WorkerExit(reason, killed?.Culprit, code, inFlight))) return;
+
+        // Every outstanding evaluation and load ends now; null tells the waiter "the worker went away".
+        foreach (var id in _pending.Keys.ToArray())
+            if (_pending.TryRemove(id, out var pending)) pending.Complete(null);
+        foreach (var id in _loads.Keys.ToArray())
+            if (_loads.TryRemove(id, out var load)) load.TrySetCanceled();
+        Volatile.Read(ref _diag)?.TrySetCanceled();
+        _outbound.Writer.TryComplete();
+    }
+
+    private static string SafeExitCode(Process process)
+    {
+        try { return process.HasExited ? process.ExitCode.ToString(System.Globalization.CultureInfo.InvariantCulture) : "?"; }
+        catch (InvalidOperationException) { return "?"; }
+    }
+
+    private static void TryDeleteDirectory(string dir)
+    {
+        try { if (Directory.Exists(dir)) Directory.Delete(dir, recursive: true); } catch { /* temp dir; best effort */ }
+    }
+
+    /// <summary>A key's compiled form in this worker.</summary>
+    internal sealed class LoadEntry
+    {
+        private readonly TaskCompletionSource<LoadEntry?> _ready = new(TaskCreationOptions.RunContinuationsAsynchronously);
+
+        public LoadEntry(string sourceHash, IReadOnlyList<string> inputPaths)
+        {
+            SourceHash = sourceHash;
+            InputPaths = inputPaths;
+            var slots = new Dictionary<string, uint>(inputPaths.Count, StringComparer.Ordinal);
+            for (var i = 0; i < inputPaths.Count; i++) slots[inputPaths[i]] = (uint)i;
+            Slots = slots;
+        }
+
+        public string SourceHash { get; }
+
+        public IReadOnlyList<string> InputPaths { get; }
+
+        /// <summary>Path → slot in the registered order.</summary>
+        public IReadOnlyDictionary<string, uint> Slots { get; }
+
+        /// <summary>The worker's verdict (null until it arrives).</summary>
+        public LoadOutcome? Outcome { get; private set; }
+
+        public Task<LoadEntry?> Ready => _ready.Task;
+
+        public bool SameSlots(IReadOnlyList<string> inputPaths)
+        {
+            if (inputPaths.Count != InputPaths.Count) return false;
+            for (var i = 0; i < inputPaths.Count; i++)
+                if (!string.Equals(inputPaths[i], InputPaths[i], StringComparison.Ordinal)) return false;
+            return true;
+        }
+
+        public void Complete(LoadOutcome? outcome)
+        {
+            Outcome = outcome;
+            _ready.TrySetResult(outcome is null ? null : this);
+        }
+    }
+}
+
+/// <summary>One evaluation outstanding on a worker.</summary>
+internal sealed class PendingEval
+{
+    private readonly TaskCompletionSource<EvalResult?> _completion = new(TaskCreationOptions.RunContinuationsAsynchronously);
+
+    public PendingEval(string key, ulong evalId)
+    {
+        Key = key;
+        EvalId = evalId;
+    }
+
+    /// <summary>The scoped key.</summary>
+    public string Key { get; }
+
+    /// <summary>The eval id on the wire.</summary>
+    public ulong EvalId { get; }
+
+    /// <summary>The worker's result, or null when the worker ended first.</summary>
+    public Task<EvalResult?> Completion => _completion.Task;
+
+    public void Complete(EvalResult? result) => _completion.TrySetResult(result);
+}

src/Core/ZB.MOM.WW.OtOpcUa.Core.Scripting.OutOfProcess/WorkerShard.cs

@@ -0,0 +1,249 @@
+using System.Diagnostics;
+using System.Diagnostics.Metrics;
+using Serilog;
+using ZB.MOM.WW.OtOpcUa.Commons.Observability;
+using ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol.V1;
+
+namespace ZB.MOM.WW.OtOpcUa.Core.Scripting.OutOfProcess;
+
+/// <summary>
+///     Supervises one shard's worker process (design §3.3, §5.3.5): starts it lazily on first use, reports its end to
+///     the runner (for attribution), and restarts it after an exponential backoff — 250 ms doubling to a 30 s cap with
+///     ±20 % jitter, reset once a worker has stayed up for 60 s. It never runs a script in the host when the worker
+///     cannot start (fail closed, §14 #4): <see cref="GetReadyAsync"/> returns null and the caller reports
+///     <c>BadResourceUnavailable</c>.
+/// </summary>
+internal sealed class WorkerShard : IAsyncDisposable
+{
+    internal static readonly TimeSpan InitialBackoff = TimeSpan.FromMilliseconds(250);
+    internal static readonly TimeSpan MaxBackoff = TimeSpan.FromSeconds(30);
+    internal static readonly TimeSpan HealthyResetAfter = TimeSpan.FromSeconds(60);
+
+    private static readonly Counter<long> StartsCounter = OtOpcUaTelemetry.Meter.CreateCounter<long>(
+        "otopcua.script.worker.starts", unit: "{process}", description: "ScriptWorker processes started (tag: shard).");
+
+    private static readonly Counter<long> ExitsCounter = OtOpcUaTelemetry.Meter.CreateCounter<long>(
+        "otopcua.script.worker.exits", unit: "{process}",
+        description: "ScriptWorker processes ended (tags: shard, reason = clean | killed_deadline | killed_heartbeat | killed_load | crash | protocol | disposed).");
+
+    private readonly Func<CancellationToken, Task<WorkerConnection>> _launch;
+    private readonly Action<WorkerShard, WorkerExit> _onExit;
+    private readonly ILogger _log;
+    private readonly object _gate = new();
+    private readonly Random _jitter = new();
+    private WorkerConnection? _current;
+    private Task<WorkerConnection?>? _starting;
+    private long _backoffUntil;
+    private int _consecutiveFailures;
+    private bool _disposed;
+
+    public WorkerShard(string label, bool isolation, Func<CancellationToken, Task<WorkerConnection>> launch,
+        Action<WorkerShard, WorkerExit> onExit, ILogger log)
+    {
+        Label = label;
+        IsIsolation = isolation;
+        _launch = launch;
+        _onExit = onExit;
+        _log = log;
+        // The isolation worker runs one evaluation at a time, so a crash there names exactly one key (design §5.3.3).
+        IsolationGate = isolation ? new SemaphoreSlim(1, 1) : null;
+    }
+
+    /// <summary>The shard label (<c>0</c>…<c>K-1</c>, or <c>iso</c>).</summary>
+    public string Label { get; }
+
+    /// <summary>Whether this is the isolation ("penalty box") worker.</summary>
+    public bool IsIsolation { get; }
+
+    /// <summary>Serialises evaluations on the isolation worker; null on a normal shard.</summary>
+    public SemaphoreSlim? IsolationGate { get; }
+
+    /// <summary>The live worker, if any (diagnostics / tests).</summary>
+    public WorkerConnection? Current
+    {
+        get { lock (_gate) return _current is { IsAlive: true } c ? c : null; }
+    }
+
+    /// <summary>Consecutive start failures and crashes since the last healthy period (diagnostics / tests).</summary>
+    public int ConsecutiveFailures
+    {
+        get { lock (_gate) return _consecutiveFailures; }
+    }
+
+    /// <summary>
+    ///     The ready worker, starting one if needed. Waits at most <paramref name="grace"/> — through a start in progress
+    ///     or a backoff — and returns null if no worker is ready by then.
+    /// </summary>
+    /// <param name="grace">How long to wait.</param>
+    /// <param name="ct">Cancellation.</param>
+    /// <returns>The worker, or null.</returns>
+    public async Task<WorkerConnection?> GetReadyAsync(TimeSpan grace, CancellationToken ct)
+    {
+        var deadline = Stopwatch.GetTimestamp() + (long)(grace.TotalSeconds * Stopwatch.Frequency);
+        while (true)
+        {
+            Task<WorkerConnection?> starting;
+            TimeSpan wait;
+            lock (_gate)
+            {
+                if (_disposed) return null;
+                if (_current is { IsAlive: true } live) return live;
+                var now = Stopwatch.GetTimestamp();
+                if (_starting is null && now >= _backoffUntil)
+                {
+                    _starting = StartCoreAsync();
+                }
+                if (_starting is not null)
+                {
+                    starting = _starting;
+                    wait = TimeSpan.Zero;
+                }
+                else
+                {
+                    starting = null!;
+                    wait = Stopwatch.GetElapsedTime(now, _backoffUntil);
+                }
+            }
+
+            var remaining = Stopwatch.GetElapsedTime(Stopwatch.GetTimestamp(), deadline);
+            if (remaining <= TimeSpan.Zero) return null;
+            if (starting is not null)
+            {
+                try
+                {
+                    var started = await starting.WaitAsync(remaining, ct).ConfigureAwait(false);
+                    if (started is { IsAlive: true }) return started;
+                }
+                catch (TimeoutException)
+                {
+                    return null;
+                }
+                continue;
+            }
+            if (wait > remaining) return null;
+            await Task.Delay(wait, ct).ConfigureAwait(false);
+        }
+    }
+
+    private async Task<WorkerConnection?> StartCoreAsync()
+    {
+        await Task.Yield();
+        WorkerConnection? connection = null;
+        try
+        {
+            connection = await _launch(CancellationToken.None).ConfigureAwait(false);
+            StartsCounter.Add(1, new KeyValuePair<string, object?>("shard", Label));
+            _log.Information("ScriptWorker[{Shard}] started, pid {Pid}", Label, connection.Pid);
+            var started = connection;
+            _ = started.Exited.ContinueWith(t => OnExited(started, t.Result), CancellationToken.None,
+                TaskContinuationOptions.ExecuteSynchronously | TaskContinuationOptions.OnlyOnRanToCompletion, TaskScheduler.Default);
+            lock (_gate)
+            {
+                _starting = null;
+                if (_disposed)
+                {
+                    _ = started.DisposeAsync().AsTask();
+                    return null;
+                }
+                _current = started;
+            }
+            return started;
+        }
+        catch (Exception ex)
+        {
+            _log.Error(ex, "ScriptWorker[{Shard}] failed to start; scripts on it report runner unavailable until it does", Label);
+            lock (_gate)
+            {
+                _starting = null;
+                ScheduleBackoffLocked();
+            }
+            if (connection is not null) await connection.DisposeAsync().ConfigureAwait(false);
+            return null;
+        }
+    }
+
+    private void OnExited(WorkerConnection connection, WorkerExit exit)
+    {
+        ExitsCounter.Add(1, new KeyValuePair<string, object?>("shard", Label),
+            new KeyValuePair<string, object?>("reason", MetricReason(exit.Reason)));
+        lock (_gate)
+        {
+            if (ReferenceEquals(_current, connection)) _current = null;
+            if (!_disposed)
+            {
+                if (Stopwatch.GetElapsedTime(connection.ReadyTimestamp) >= HealthyResetAfter) _consecutiveFailures = 0;
+                ScheduleBackoffLocked();
+            }
+        }
+        if (exit.Reason != WorkerExitReason.Disposed)
+        {
+            _log.Warning("ScriptWorker[{Shard}] pid {Pid} ended: {Reason} (exit code {ExitCode}, culprit {Culprit}, {InFlight} evaluation(s) in flight)",
+                Label, connection.Pid, exit.Reason, exit.ExitCode, exit.CulpritKey ?? "none", exit.InFlightKeys.Count);
+        }
+        try { _onExit(this, exit); }
+        catch (Exception ex) { _log.Error(ex, "ScriptWorker[{Shard}] exit handler threw", Label); }
+        _ = connection.DisposeAsync().AsTask();
+    }
+
+    private void ScheduleBackoffLocked()
+    {
+        _consecutiveFailures++;
+        var delay = NextBackoff(_consecutiveFailures, _jitter.NextDouble());
+        _backoffUntil = Stopwatch.GetTimestamp() + (long)(delay.TotalSeconds * Stopwatch.Frequency);
+    }
+
+    /// <summary>The restart delay after <paramref name="failures"/> consecutive failures (design §5.3.5).</summary>
+    /// <param name="failures">1 for the first failure.</param>
+    /// <param name="unitJitter">A sample in [0, 1) mapped to ±20 %.</param>
+    /// <returns>The delay.</returns>
+    internal static TimeSpan NextBackoff(int failures, double unitJitter)
+    {
+        var exponent = Math.Clamp(failures - 1, 0, 30);
+        var baseMs = Math.Min(MaxBackoff.TotalMilliseconds, InitialBackoff.TotalMilliseconds * Math.Pow(2, exponent));
+        var factor = 0.8 + (0.4 * Math.Clamp(unitJitter, 0, 1));
+        return TimeSpan.FromMilliseconds(Math.Min(MaxBackoff.TotalMilliseconds * 1.2, baseMs * factor));
+    }
+
+    private static string MetricReason(WorkerExitReason reason) => reason switch
+    {
+        WorkerExitReason.Clean => "clean",
+        WorkerExitReason.KilledDeadline => "killed_deadline",
+        WorkerExitReason.KilledHeartbeat => "killed_heartbeat",
+        WorkerExitReason.KilledLoadTimeout => "killed_load",
+        WorkerExitReason.ProtocolFault => "protocol",
+        WorkerExitReason.Disposed => "disposed",
+        _ => "crash",
+    };
+
+    /// <summary>Stops the shard's worker.</summary>
+    /// <returns>A task that completes when the worker has ended.</returns>
+    public async ValueTask DisposeAsync()
+    {
+        WorkerConnection? current;
+        Task<WorkerConnection?>? starting;
+        lock (_gate)
+        {
+            _disposed = true;
+            current = _current;
+            starting = _starting;
+            _current = null;
+        }
+        if (starting is not null)
+        {
+            try { current ??= await starting.WaitAsync(TimeSpan.FromSeconds(15)).ConfigureAwait(false); } catch { /* shutting down */ }
+        }
+        if (current is not null) await current.DisposeAsync().ConfigureAwait(false);
+        IsolationGate?.Dispose();
+    }
+
+    /// <summary>Maps a context kind to the wire enum.</summary>
+    /// <param name="kind">The kind.</param>
+    /// <returns>The wire kind.</returns>
+    internal static ContextKind ToWire(ScriptContextKind kind) => kind switch
+    {
+        ScriptContextKind.VirtualTag => ContextKind.VirtualTag,
+        ScriptContextKind.Calculation => ContextKind.Calculation,
+        ScriptContextKind.AlarmPredicate => ContextKind.AlarmPredicate,
+        _ => ContextKind.Unspecified,
+    };
+}

src/Core/ZB.MOM.WW.OtOpcUa.Core.Scripting.OutOfProcess/ZB.MOM.WW.OtOpcUa.Core.Scripting.OutOfProcess.csproj

@@ -0,0 +1,20 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <!-- lmxopcua#780 — the host side of the out-of-process, pre-emptible script runner (design §3, §5, §9): worker
+         launch + pipe handshake, the per-shard supervisor, attribution and quarantine. Selected by
+         Scripting:Runner=OutOfProcess; nothing here runs under the InProcess default. -->
+    <PropertyGroup>
+        <RootNamespace>ZB.MOM.WW.OtOpcUa.Core.Scripting.OutOfProcess</RootNamespace>
+        <GenerateDocumentationFile>true</GenerateDocumentationFile>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <ProjectReference Include="..\ZB.MOM.WW.OtOpcUa.Core.Scripting\ZB.MOM.WW.OtOpcUa.Core.Scripting.csproj"/>
+        <ProjectReference Include="..\ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol\ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol.csproj"/>
+    </ItemGroup>
+
+    <ItemGroup>
+        <InternalsVisibleTo Include="ZB.MOM.WW.OtOpcUa.ScriptWorker.Tests"/>
+    </ItemGroup>
+
+</Project>

src/Core/ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol/Protos/script_worker.proto

@@ -0,0 +1,214 @@
+// lmxopcua#780 — host <-> ScriptWorker IPC (design docs/plans/2026-11-09-out-of-process-script-runner-design.md §4).
+// Framing: 4-byte little-endian length prefix + one serialized Envelope. Zero-length and oversize frames are protocol
+// faults. One request frame and one reply frame per evaluation; the only other worker->host traffic is logs and
+// heartbeats. Bump protocol_version on any incompatible change.
+syntax = "proto3";
+
+package otopcua.scriptworker.v1;
+
+option csharp_namespace = "ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol.V1";
+
+message Envelope {
+  uint32 protocol_version = 1;
+  uint64 seq = 2;
+  oneof body {
+    Hello hello = 10;               // host -> worker, first frame
+    Ready ready = 11;               // worker -> host, reply to Hello
+    LoadScripts load = 12;          // host -> worker
+    LoadResult load_result = 13;    // worker -> host
+    Unload unload = 14;             // host -> worker
+    EvalBatch eval = 15;            // host -> worker
+    EvalResults results = 16;       // worker -> host, streamed as runs complete
+    LogBatch logs = 17;             // worker -> host, fire-and-forget, bounded
+    Heartbeat heartbeat = 18;       // worker -> host, every heartbeat_interval_ms
+    Shutdown shutdown = 19;         // host -> worker
+    Fault fault = 20;               // either way; the sender closes after it
+    DiagnosticsRequest diag_request = 21;  // host -> worker (tests / ops)
+    DiagnosticsReply diag_reply = 22;      // worker -> host
+    Cancel cancel = 23;                    // host -> worker, at the soft deadline
+  }
+}
+
+message Hello {
+  string nonce = 1;                 // must be echoed in Ready
+  uint32 max_frame_bytes = 2;
+  uint32 eval_threads = 3;          // the worker's scheduler width; 1 for the isolation worker
+  uint32 queue_capacity = 4;        // queued evaluations above this answer BUSY
+  uint32 hard_grace_ms = 5;         // worker watchdog: fail fast past soft + grace (+ margin)
+  uint32 heartbeat_interval_ms = 6;
+  uint32 max_log_lines = 7;         // outbound log buffer cap
+}
+
+message Ready {
+  string nonce = 1;
+  int32 pid = 2;
+  string runtime_version = 3;
+}
+
+enum ContextKind {
+  CONTEXT_KIND_UNSPECIFIED = 0;
+  VIRTUAL_TAG = 1;
+  CALCULATION = 2;
+  ALARM_PREDICATE = 3;
+}
+
+message ScriptSource {
+  string key = 1;
+  bytes source_sha256 = 2;
+  ContextKind kind = 3;
+  string source = 4;
+  repeated string input_paths = 5;  // slot order for EvalRequest.inputs
+}
+
+message LoadScripts {
+  uint64 load_id = 1;
+  repeated ScriptSource scripts = 2;
+}
+
+message LoadOutcome {
+  string key = 1;
+  bool ok = 2;
+  ScriptError error = 3;            // COMPILE or SANDBOX when !ok
+}
+
+message LoadResult {
+  uint64 load_id = 1;
+  repeated LoadOutcome outcomes = 2;
+}
+
+message Unload {
+  repeated string keys = 1;
+}
+
+message EvalBatch {
+  repeated EvalRequest items = 1;
+}
+
+message EvalRequest {
+  uint64 eval_id = 1;
+  string key = 2;
+  repeated Input inputs = 3;
+  int64 now_utc_ticks = 4;          // ctx.Now (host clock)
+  uint32 soft_timeout_ms = 5;
+  uint32 hard_grace_ms = 6;         // this run's G; 0 = Hello.hard_grace_ms
+}
+
+message Input {
+  uint32 slot = 1;                  // index into ScriptSource.input_paths; ignored when path is set
+  Variant value = 2;
+  uint32 status_code = 3;
+  int64 source_ts_ticks = 4;        // 0 = null
+  int64 server_ts_ticks = 5;
+  string path = 6;                  // inline path for an input with no registered slot
+  bool unsupported = 7;             // the host could not encode the value's CLR type (see unsupported_type)
+  string unsupported_type = 8;
+}
+
+message EvalResult {
+  uint64 eval_id = 1;
+  oneof outcome {
+    Variant value = 2;
+    bool predicate = 3;
+    ScriptError error = 4;
+  }
+  uint64 allocated_bytes = 5;       // GC.GetAllocatedBytesForCurrentThread around the run
+  uint32 run_micros = 6;
+}
+
+message EvalResults {
+  repeated EvalResult items = 1;
+}
+
+message ScriptError {
+  enum Kind {
+    THREW = 0;
+    COMPILE = 1;
+    SANDBOX = 2;
+    SOFT_TIMEOUT = 3;
+    UNSUPPORTED_TYPE = 4;
+    BUSY = 5;
+    NOT_LOADED = 6;
+  }
+  Kind kind = 1;
+  string message = 2;
+}
+
+message Variant {
+  enum TypeTag {
+    NULL = 0;
+    BOOLEAN = 1;
+    SBYTE = 2;
+    BYTE = 3;
+    INT16 = 4;
+    UINT16 = 5;
+    INT32 = 6;
+    UINT32 = 7;
+    INT64 = 8;
+    UINT64 = 9;
+    FLOAT = 10;
+    DOUBLE = 11;
+    STRING = 12;
+    DATETIME_UTC = 13;
+    ARRAY = 14;
+  }
+  TypeTag type = 1;                 // the exact CLR type: (short)ctx.GetTag(x).Value must keep working
+  oneof v {
+    bool b = 2;
+    sint64 i = 3;
+    uint64 u = 4;
+    double d = 5;
+    float f = 6;
+    string s = 7;
+    int64 dt_ticks = 8;
+    ArrayValue array = 9;
+  }
+}
+
+message ArrayValue {
+  Variant.TypeTag element_type = 1;
+  repeated Variant items = 2;
+}
+
+message LogBatch {
+  repeated LogLine lines = 1;
+  uint32 dropped = 2;
+}
+
+message LogLine {
+  string key = 1;
+  uint32 level = 2;                 // Serilog LogEventLevel
+  string rendered = 3;
+  string exception = 4;
+  int64 ts_ticks = 5;
+}
+
+message Heartbeat {
+  uint32 inflight = 1;
+  uint32 queued = 2;
+  int64 heap_bytes = 3;
+  uint32 gen2_count = 4;
+}
+
+message Shutdown {
+}
+
+// Sent by the host when it has answered the caller with a soft timeout: cancels the run's ctx.CancellationToken, so a
+// polling script ends itself. The worker never cancels on its own clock, which keeps the in-process ordering — the
+// caller always has its timeout before the script can observe cancellation.
+message Cancel {
+  uint64 eval_id = 1;
+}
+
+message Fault {
+  string message = 1;
+}
+
+message DiagnosticsRequest {
+}
+
+message DiagnosticsReply {
+  int32 pid = 1;
+  repeated string loaded_assemblies = 2;
+  repeated string environment_names = 3;
+  string working_directory = 4;
+}

src/Core/ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol/ScriptWorkerEnvironment.cs

@@ -0,0 +1,54 @@
+namespace ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol;
+
+/// <summary>
+///     The environment variables the host sets on a ScriptWorker (design §6). The nonce travels in the environment,
+///     never on the command line (mxaccessgw <c>WorkerBootstrap.md</c>): a command line is world-readable on most
+///     systems.
+/// </summary>
+public static class ScriptWorkerEnvironment
+{
+    /// <summary>The pipe name the worker connects to.</summary>
+    public const string PipeName = "OTOPCUA_SCRIPTWORKER_PIPE";
+
+    /// <summary>The one-time launch nonce the worker must echo in <c>Ready</c>.</summary>
+    public const string Nonce = "OTOPCUA_SCRIPTWORKER_NONCE";
+
+    /// <summary>The host's process id; the worker exits when it disappears.</summary>
+    public const string ParentPid = "OTOPCUA_SCRIPTWORKER_PARENT_PID";
+
+    /// <summary>The worker's shard label, for its own diagnostics.</summary>
+    public const string Shard = "OTOPCUA_SCRIPTWORKER_SHARD";
+
+    /// <summary>
+    ///     Exit code of a worker whose pipe reached end of stream (the host went away). Distinct from a crash so the
+    ///     host's exit reason metric can tell them apart.
+    /// </summary>
+    public const int ExitPipeClosed = 3;
+
+    /// <summary>Exit code of a worker whose handshake or framing failed.</summary>
+    public const int ExitProtocolFault = 4;
+
+    /// <summary>Exit code of a worker whose parent process disappeared.</summary>
+    public const int ExitParentGone = 5;
+
+    /// <summary>Exit code of a worker that found a forbidden assembly loaded in itself.</summary>
+    public const int ExitForbiddenAssembly = 6;
+
+    /// <summary>
+    ///     Assembly-name prefixes that must never be loaded in a worker (design §6): the host's cluster, database,
+    ///     OPC UA and secrets stacks. The worker checks itself against this list and exits if it finds one.
+    /// </summary>
+    public static readonly IReadOnlyList<string> ForbiddenAssemblyPrefixes =
+    [
+        "Akka",
+        "Microsoft.Data.SqlClient",
+        "System.Data.SqlClient",
+        "Microsoft.EntityFrameworkCore",
+        "Opc.Ua",
+        "ZB.MOM.WW.Secrets",
+        "ZB.MOM.WW.OtOpcUa.Runtime",
+        "ZB.MOM.WW.OtOpcUa.Host",
+        "ZB.MOM.WW.OtOpcUa.Driver.",
+        "Grpc.",
+    ];
+}

src/Core/ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol/ScriptWorkerFrameCodec.cs

@@ -0,0 +1,116 @@
+using System.Buffers;
+using System.Buffers.Binary;
+using Google.Protobuf;
+using ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol.V1;
+
+namespace ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol;
+
+/// <summary>
+///     Length-prefixed protobuf framing for the ScriptWorker pipe (lmxopcua#780, design §4.2): a 4-byte little-endian
+///     length, then one serialized <see cref="Envelope"/>. Copies mxaccessgw's <c>WorkerFrameProtocol</c> discipline:
+///     zero-length, oversize, truncated and unparseable frames are all a <see cref="ScriptWorkerProtocolException"/>,
+///     after which the stream is unusable and the peer is dropped.
+/// </summary>
+public static class ScriptWorkerFrameCodec
+{
+    /// <summary>The protocol version both ends put on every envelope.</summary>
+    public const uint ProtocolVersion = 1;
+
+    /// <summary>Default frame cap: 4 MiB.</summary>
+    public const int DefaultMaxFrameBytes = 4 * 1024 * 1024;
+
+    /// <summary>Writes one frame. Not thread-safe: callers serialise writes.</summary>
+    /// <param name="stream">The pipe.</param>
+    /// <param name="envelope">The envelope.</param>
+    /// <param name="maxFrameBytes">The negotiated cap; a larger envelope is refused before anything is written.</param>
+    /// <param name="ct">Cancellation.</param>
+    /// <returns>A task that completes when the frame is written (not flushed).</returns>
+    public static async ValueTask WriteAsync(Stream stream, Envelope envelope, int maxFrameBytes, CancellationToken ct = default)
+    {
+        ArgumentNullException.ThrowIfNull(stream);
+        ArgumentNullException.ThrowIfNull(envelope);
+        var size = envelope.CalculateSize();
+        if (size == 0) throw new ScriptWorkerProtocolException("refusing to write an empty frame");
+        if (size > maxFrameBytes)
+            throw new ScriptWorkerProtocolException($"frame of {size} bytes exceeds the {maxFrameBytes}-byte cap");
+
+        var buffer = ArrayPool<byte>.Shared.Rent(size + 4);
+        try
+        {
+            BinaryPrimitives.WriteInt32LittleEndian(buffer, size);
+            envelope.WriteTo(new Span<byte>(buffer, 4, size));
+            await stream.WriteAsync(buffer.AsMemory(0, size + 4), ct).ConfigureAwait(false);
+        }
+        finally
+        {
+            ArrayPool<byte>.Shared.Return(buffer);
+        }
+    }
+
+    /// <summary>Reads one frame.</summary>
+    /// <param name="stream">The pipe.</param>
+    /// <param name="maxFrameBytes">The negotiated cap.</param>
+    /// <param name="ct">Cancellation.</param>
+    /// <returns>The envelope, or null on a clean end of stream at a frame boundary.</returns>
+    /// <exception cref="ScriptWorkerProtocolException">A zero-length, oversize, truncated or unparseable frame.</exception>
+    public static async ValueTask<Envelope?> ReadAsync(Stream stream, int maxFrameBytes, CancellationToken ct = default)
+    {
+        ArgumentNullException.ThrowIfNull(stream);
+        var header = new byte[4];
+        var got = await ReadFullyAsync(stream, header, ct).ConfigureAwait(false);
+        if (got == 0) return null;
+        if (got < 4) throw new ScriptWorkerProtocolException("truncated frame header");
+
+        var size = BinaryPrimitives.ReadInt32LittleEndian(header);
+        if (size == 0) throw new ScriptWorkerProtocolException("zero-length frame");
+        if (size < 0 || size > maxFrameBytes)
+            throw new ScriptWorkerProtocolException($"frame length {size} is outside 1..{maxFrameBytes}");
+
+        var body = ArrayPool<byte>.Shared.Rent(size);
+        try
+        {
+            var read = await ReadFullyAsync(stream, body.AsMemory(0, size), ct).ConfigureAwait(false);
+            if (read < size) throw new ScriptWorkerProtocolException($"truncated frame: {read} of {size} bytes");
+            Envelope envelope;
+            try
+            {
+                envelope = Envelope.Parser.ParseFrom(body, 0, size);
+            }
+            catch (InvalidProtocolBufferException ex)
+            {
+                throw new ScriptWorkerProtocolException($"unparseable frame: {ex.Message}", ex);
+            }
+            if (envelope.ProtocolVersion != ProtocolVersion)
+                throw new ScriptWorkerProtocolException(
+                    $"protocol version {envelope.ProtocolVersion} is not the supported {ProtocolVersion}");
+            if (envelope.BodyCase == Envelope.BodyOneofCase.None)
+                throw new ScriptWorkerProtocolException("frame carries no body");
+            return envelope;
+        }
+        finally
+        {
+            ArrayPool<byte>.Shared.Return(body);
+        }
+    }
+
+    private static async ValueTask<int> ReadFullyAsync(Stream stream, Memory<byte> buffer, CancellationToken ct)
+    {
+        var total = 0;
+        while (total < buffer.Length)
+        {
+            var n = await stream.ReadAsync(buffer[total..], ct).ConfigureAwait(false);
+            if (n == 0) break;
+            total += n;
+        }
+        return total;
+    }
+}
+
+/// <summary>A framing or schema violation on the ScriptWorker pipe; the connection is dropped.</summary>
+public sealed class ScriptWorkerProtocolException : Exception
+{
+    /// <summary>Initializes the exception.</summary>
+    /// <param name="message">What was wrong.</param>
+    /// <param name="inner">The underlying parser error, if any.</param>
+    public ScriptWorkerProtocolException(string message, Exception? inner = null) : base(message, inner) { }
+}

src/Core/ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol/VariantCodec.cs

@@ -0,0 +1,159 @@
+using ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol.V1;
+
+namespace ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol;
+
+/// <summary>
+///     CLR value ↔ <see cref="Variant"/> (design §4.4). The exact boxed CLR type survives the round trip — a script
+///     doing <c>(short)ctx.GetTag(x).Value</c> throws <see cref="InvalidCastException"/> if a <c>short</c> arrives as an
+///     <c>int</c> — so the type tag names the CLR type, not just an OPC UA one. A type with no tag is never converted:
+///     <see cref="TryEncode"/> refuses it, and the caller reports <c>UNSUPPORTED_TYPE</c> (design §14 #11).
+/// </summary>
+public static class VariantCodec
+{
+    /// <summary>Encodes <paramref name="value"/>.</summary>
+    /// <param name="value">The boxed CLR value (null allowed).</param>
+    /// <param name="variant">The encoded variant when supported.</param>
+    /// <param name="unsupportedType">The CLR type name when not supported.</param>
+    /// <returns><c>true</c> when the type has a tag.</returns>
+    public static bool TryEncode(object? value, out Variant variant, out string? unsupportedType)
+    {
+        unsupportedType = null;
+        variant = new Variant();
+        switch (value)
+        {
+            case null: variant.Type = Variant.Types.TypeTag.Null; return true;
+            case bool b: variant.Type = Variant.Types.TypeTag.Boolean; variant.B = b; return true;
+            case sbyte v: variant.Type = Variant.Types.TypeTag.Sbyte; variant.I = v; return true;
+            case byte v: variant.Type = Variant.Types.TypeTag.Byte; variant.U = v; return true;
+            case short v: variant.Type = Variant.Types.TypeTag.Int16; variant.I = v; return true;
+            case ushort v: variant.Type = Variant.Types.TypeTag.Uint16; variant.U = v; return true;
+            case int v: variant.Type = Variant.Types.TypeTag.Int32; variant.I = v; return true;
+            case uint v: variant.Type = Variant.Types.TypeTag.Uint32; variant.U = v; return true;
+            case long v: variant.Type = Variant.Types.TypeTag.Int64; variant.I = v; return true;
+            case ulong v: variant.Type = Variant.Types.TypeTag.Uint64; variant.U = v; return true;
+            case float v: variant.Type = Variant.Types.TypeTag.Float; variant.F = v; return true;
+            case double v: variant.Type = Variant.Types.TypeTag.Double; variant.D = v; return true;
+            case string v: variant.Type = Variant.Types.TypeTag.String; variant.S = v; return true;
+            case DateTime v:
+                variant.Type = Variant.Types.TypeTag.DatetimeUtc;
+                variant.DtTicks = ToUtc(v).Ticks;
+                return true;
+            case Array array when array.Rank == 1 && TryElementTag(array.GetType().GetElementType()!, out var elementTag):
+            {
+                var av = new ArrayValue { ElementType = elementTag };
+                foreach (var item in array)
+                {
+                    if (!TryEncode(item, out var element, out unsupportedType)) return false;
+                    av.Items.Add(element);
+                }
+                variant.Type = Variant.Types.TypeTag.Array;
+                variant.Array = av;
+                return true;
+            }
+            default:
+                unsupportedType = value.GetType().FullName ?? value.GetType().Name;
+                return false;
+        }
+    }
+
+    /// <summary>Decodes <paramref name="variant"/> back to the boxed CLR value it was encoded from.</summary>
+    /// <param name="variant">The variant.</param>
+    /// <returns>The boxed value.</returns>
+    /// <exception cref="ScriptWorkerProtocolException">An unknown tag, or a payload that does not match the tag.</exception>
+    public static object? Decode(Variant? variant)
+    {
+        if (variant is null) return null;
+        return variant.Type switch
+        {
+            Variant.Types.TypeTag.Null => null,
+            Variant.Types.TypeTag.Boolean => Expect(variant, Variant.VOneofCase.B).B,
+            Variant.Types.TypeTag.Sbyte => checked((sbyte)Expect(variant, Variant.VOneofCase.I).I),
+            Variant.Types.TypeTag.Byte => checked((byte)Expect(variant, Variant.VOneofCase.U).U),
+            Variant.Types.TypeTag.Int16 => checked((short)Expect(variant, Variant.VOneofCase.I).I),
+            Variant.Types.TypeTag.Uint16 => checked((ushort)Expect(variant, Variant.VOneofCase.U).U),
+            Variant.Types.TypeTag.Int32 => checked((int)Expect(variant, Variant.VOneofCase.I).I),
+            Variant.Types.TypeTag.Uint32 => checked((uint)Expect(variant, Variant.VOneofCase.U).U),
+            Variant.Types.TypeTag.Int64 => Expect(variant, Variant.VOneofCase.I).I,
+            Variant.Types.TypeTag.Uint64 => Expect(variant, Variant.VOneofCase.U).U,
+            Variant.Types.TypeTag.Float => Expect(variant, Variant.VOneofCase.F).F,
+            Variant.Types.TypeTag.Double => Expect(variant, Variant.VOneofCase.D).D,
+            Variant.Types.TypeTag.String => Expect(variant, Variant.VOneofCase.S).S,
+            Variant.Types.TypeTag.DatetimeUtc => new DateTime(Expect(variant, Variant.VOneofCase.DtTicks).DtTicks, DateTimeKind.Utc),
+            Variant.Types.TypeTag.Array => DecodeArray(Expect(variant, Variant.VOneofCase.Array).Array),
+            _ => throw new ScriptWorkerProtocolException($"unknown variant type tag {(int)variant.Type}"),
+        };
+    }
+
+    /// <summary>A <see cref="DateTime"/> as UTC: a <c>Local</c> value is converted; an <c>Unspecified</c> one is taken as UTC.</summary>
+    /// <param name="value">The value.</param>
+    /// <returns>The UTC value.</returns>
+    public static DateTime ToUtc(DateTime value) => value.Kind switch
+    {
+        DateTimeKind.Utc => value,
+        DateTimeKind.Local => value.ToUniversalTime(),
+        _ => DateTime.SpecifyKind(value, DateTimeKind.Utc),
+    };
+
+    private static Variant Expect(Variant variant, Variant.VOneofCase expected)
+    {
+        // proto3 drops a default scalar (0, false, "") from the oneof, so an absent payload is the default value.
+        if (variant.VCase != expected && variant.VCase != Variant.VOneofCase.None)
+            throw new ScriptWorkerProtocolException($"variant tagged {variant.Type} carries a {variant.VCase} payload");
+        return variant;
+    }
+
+    private static Array DecodeArray(ArrayValue? array)
+    {
+        if (array is null) throw new ScriptWorkerProtocolException("array variant without an array payload");
+        var elementType = ClrType(array.ElementType);
+        var result = Array.CreateInstance(elementType, array.Items.Count);
+        for (var i = 0; i < array.Items.Count; i++)
+        {
+            var item = array.Items[i];
+            if (item.Type != array.ElementType && item.Type != Variant.Types.TypeTag.Null)
+                throw new ScriptWorkerProtocolException($"array of {array.ElementType} holds a {item.Type} element");
+            result.SetValue(Decode(item), i);
+        }
+        return result;
+    }
+
+    private static bool TryElementTag(Type elementType, out Variant.Types.TypeTag tag)
+    {
+        tag = elementType switch
+        {
+            _ when elementType == typeof(bool) => Variant.Types.TypeTag.Boolean,
+            _ when elementType == typeof(sbyte) => Variant.Types.TypeTag.Sbyte,
+            _ when elementType == typeof(byte) => Variant.Types.TypeTag.Byte,
+            _ when elementType == typeof(short) => Variant.Types.TypeTag.Int16,
+            _ when elementType == typeof(ushort) => Variant.Types.TypeTag.Uint16,
+            _ when elementType == typeof(int) => Variant.Types.TypeTag.Int32,
+            _ when elementType == typeof(uint) => Variant.Types.TypeTag.Uint32,
+            _ when elementType == typeof(long) => Variant.Types.TypeTag.Int64,
+            _ when elementType == typeof(ulong) => Variant.Types.TypeTag.Uint64,
+            _ when elementType == typeof(float) => Variant.Types.TypeTag.Float,
+            _ when elementType == typeof(double) => Variant.Types.TypeTag.Double,
+            _ when elementType == typeof(string) => Variant.Types.TypeTag.String,
+            _ when elementType == typeof(DateTime) => Variant.Types.TypeTag.DatetimeUtc,
+            _ => Variant.Types.TypeTag.Null,
+        };
+        return tag != Variant.Types.TypeTag.Null;
+    }
+
+    private static Type ClrType(Variant.Types.TypeTag tag) => tag switch
+    {
+        Variant.Types.TypeTag.Boolean => typeof(bool),
+        Variant.Types.TypeTag.Sbyte => typeof(sbyte),
+        Variant.Types.TypeTag.Byte => typeof(byte),
+        Variant.Types.TypeTag.Int16 => typeof(short),
+        Variant.Types.TypeTag.Uint16 => typeof(ushort),
+        Variant.Types.TypeTag.Int32 => typeof(int),
+        Variant.Types.TypeTag.Uint32 => typeof(uint),
+        Variant.Types.TypeTag.Int64 => typeof(long),
+        Variant.Types.TypeTag.Uint64 => typeof(ulong),
+        Variant.Types.TypeTag.Float => typeof(float),
+        Variant.Types.TypeTag.Double => typeof(double),
+        Variant.Types.TypeTag.String => typeof(string),
+        Variant.Types.TypeTag.DatetimeUtc => typeof(DateTime),
+        _ => throw new ScriptWorkerProtocolException($"array element type {tag} is not supported"),
+    };
+}

src/Core/ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol/ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol.csproj

@@ -0,0 +1,28 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <RootNamespace>ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol</RootNamespace>
+        <GenerateDocumentationFile>true</GenerateDocumentationFile>
+        <!-- protoc-generated members carry no XML docs. -->
+        <NoWarn>$(NoWarn);CS1591</NoWarn>
+    </PropertyGroup>
+
+    <!-- lmxopcua#780: the host <-> ScriptWorker frame protocol (design §4). Shared by the host-side runner and the
+         worker, so it references nothing but Google.Protobuf: the worker's assembly set stays small (design §6). -->
+    <ItemGroup>
+        <PackageReference Include="Google.Protobuf"/>
+        <PackageReference Include="Grpc.Tools">
+            <PrivateAssets>all</PrivateAssets>
+            <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+        </PackageReference>
+    </ItemGroup>
+
+    <ItemGroup>
+        <Protobuf Include="Protos\script_worker.proto" GrpcServices="None"/>
+    </ItemGroup>
+
+    <ItemGroup>
+        <InternalsVisibleTo Include="ZB.MOM.WW.OtOpcUa.ScriptWorker.Tests"/>
+    </ItemGroup>
+
+</Project>

src/Core/ZB.MOM.WW.OtOpcUa.Core.Scripting/IScriptRunner.cs

@@ -0,0 +1,137 @@
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+namespace ZB.MOM.WW.OtOpcUa.Core.Scripting;
+
+/// <summary>
+///     The execution seam every host script owner can run a compiled script through (lmxopcua#780, design §11): a
+///     script key, its source, its input snapshots and its budget go in; one <see cref="ScriptRunOutcome"/> comes
+///     out. Implementations never throw for script faults.
+/// </summary>
+/// <remarks>
+///     <para>
+///         <see cref="InProcessScriptRunner"/> is today's <see cref="ScriptRunGuard"/> + <see cref="CompiledScriptCache{TContext, TResult}"/>
+///         behind this interface (the parity baseline). The out-of-process runner
+///         (<c>ZB.MOM.WW.OtOpcUa.Core.Scripting.Runner</c>) runs the same compile in a pre-emptible worker process.
+///         The passthrough fast path (<c>PassthroughScript</c>) never reaches a runner: it runs no user code.
+///     </para>
+///     <para>
+///         Keys are namespaced by <see cref="ScriptInvocation.Kind"/>, so a virtual-tag id and a calc RawPath that
+///         happen to be equal never share quarantine state, and <see cref="Reset"/> for one seam leaves the other
+///         seams' quarantines alone.
+///     </para>
+/// </remarks>
+public interface IScriptRunner
+{
+    /// <summary>Runs one compiled evaluation.</summary>
+    /// <param name="invocation">What to run.</param>
+    /// <param name="ct">Caller cancellation (shutdown); wins over the budget.</param>
+    /// <returns>The outcome; never faults for a script failure.</returns>
+    Task<ScriptRunOutcome> RunAsync(ScriptInvocation invocation, CancellationToken ct = default);
+
+    /// <summary>
+    ///     The deploy boundary for one seam: lifts every quarantine and forgets every remembered compile failure of
+    ///     <paramref name="kind"/>, and drops its compiled scripts.
+    /// </summary>
+    /// <param name="kind">The seam's context kind.</param>
+    void Reset(ScriptContextKind kind);
+
+    /// <summary>The keys of <paramref name="kind"/> currently quarantined.</summary>
+    /// <param name="kind">The seam's context kind.</param>
+    /// <returns>The quarantined keys (un-namespaced).</returns>
+    IReadOnlyCollection<string> QuarantinedKeys(ScriptContextKind kind);
+}
+
+/// <summary>Which script context (and result type) a script compiles against.</summary>
+public enum ScriptContextKind
+{
+    /// <summary>A virtual tag: <c>VirtualTagContext</c> → <c>object?</c>.</summary>
+    VirtualTag = 1,
+
+    /// <summary>A Calculation tag: <c>VirtualTagContext</c> → <c>object?</c>.</summary>
+    Calculation = 2,
+
+    /// <summary>A scripted-alarm predicate: <c>AlarmPredicateContext</c> → <c>bool</c> (not run out of process yet).</summary>
+    AlarmPredicate = 3,
+}
+
+/// <summary>One evaluation handed to an <see cref="IScriptRunner"/>.</summary>
+/// <param name="Key">The script instance key (virtual-tag id, calc RawPath, alarm id).</param>
+/// <param name="Kind">The context kind.</param>
+/// <param name="Source">The script source (also its identity: a change lifts the key's quarantine).</param>
+/// <param name="Inputs">The read cache: dependency snapshots by path. Not mutated until the run completes.</param>
+/// <param name="Timeout">The soft budget <c>T</c>.</param>
+/// <param name="ScriptLogger">The per-evaluation script logger <c>ctx.Logger</c> writes through; null ⇒ a silent logger.</param>
+public sealed record ScriptInvocation(
+    string Key,
+    ScriptContextKind Kind,
+    string Source,
+    IReadOnlyDictionary<string, DataValueSnapshot> Inputs,
+    TimeSpan Timeout,
+    Serilog.ILogger? ScriptLogger = null);
+
+/// <summary>How an evaluation ended.</summary>
+public enum ScriptRunStatus
+{
+    /// <summary>The script returned <see cref="ScriptRunOutcome.Value"/>.</summary>
+    Ok = 0,
+
+    /// <summary>A script-attributable failure (threw, timed out, refused, quarantined, did not compile) — Bad as today.</summary>
+    Failed = 1,
+
+    /// <summary>
+    ///     The runner could not run the script, and it is not the script's fault: its worker restarted under it, or no
+    ///     worker became ready in time. Published as <c>BadResourceUnavailable</c> (design §9 / §14 #3).
+    /// </summary>
+    Unavailable = 2,
+}
+
+/// <summary>The result of one <see cref="IScriptRunner.RunAsync"/>.</summary>
+/// <param name="Status">How it ended.</param>
+/// <param name="Value">The script's result when <see cref="ScriptRunStatus.Ok"/>.</param>
+/// <param name="Reason">The failure reason otherwise; the same strings the evaluators have always published.</param>
+public sealed record ScriptRunOutcome(ScriptRunStatus Status, object? Value, string? Reason)
+{
+    /// <summary>Reason when the worker running the script died under it (another script's kill, a crash).</summary>
+    public const string WorkerRestartedReason = "script worker restarted";
+
+    /// <summary>Reason when no worker became ready within <see cref="ScriptWorkerOptions.UnavailableGrace"/>.</summary>
+    public const string RunnerUnavailableReason = "script runner unavailable";
+
+    /// <summary>A successful run.</summary>
+    /// <param name="value">The script's result.</param>
+    /// <returns>The outcome.</returns>
+    public static ScriptRunOutcome Ok(object? value) => new(ScriptRunStatus.Ok, value, null);
+
+    /// <summary>A script-attributable failure.</summary>
+    /// <param name="reason">The reason.</param>
+    /// <returns>The outcome.</returns>
+    public static ScriptRunOutcome Failed(string reason) => new(ScriptRunStatus.Failed, null, reason);
+
+    /// <summary>A runner-attributable failure.</summary>
+    /// <param name="reason">The reason.</param>
+    /// <returns>The outcome.</returns>
+    public static ScriptRunOutcome Unavailable(string reason) => new(ScriptRunStatus.Unavailable, null, reason);
+}
+
+/// <summary>Maps an <see cref="IScriptRunner"/> outcome onto the value seams' result type.</summary>
+public static class ScriptRunOutcomeExtensions
+{
+    /// <summary>
+    ///     <see cref="ScriptRunStatus.Ok"/> → <c>Ok(value)</c>; <see cref="ScriptRunStatus.Failed"/> → <c>Failure(reason)</c>
+    ///     (published <c>BadInternalError</c>, as today); <see cref="ScriptRunStatus.Unavailable"/> →
+    ///     <c>Unavailable(reason)</c> (published <c>BadResourceUnavailable</c>).
+    /// </summary>
+    /// <param name="outcome">The runner's outcome.</param>
+    /// <returns>The seam result.</returns>
+    public static Commons.Engines.VirtualTagEvalResult ToVirtualTagEvalResult(this ScriptRunOutcome outcome)
+    {
+        ArgumentNullException.ThrowIfNull(outcome);
+        return outcome.Status switch
+        {
+            ScriptRunStatus.Ok => Commons.Engines.VirtualTagEvalResult.Ok(outcome.Value),
+            ScriptRunStatus.Unavailable => Commons.Engines.VirtualTagEvalResult.Unavailable(
+                outcome.Reason ?? ScriptRunOutcome.RunnerUnavailableReason),
+            _ => Commons.Engines.VirtualTagEvalResult.Failure(outcome.Reason ?? "evaluator failure"),
+        };
+    }
+}

src/Core/ZB.MOM.WW.OtOpcUa.Core.Scripting/InProcessScriptRunner.cs

@@ -0,0 +1,141 @@
+using System.Collections.Concurrent;
+using Serilog;
+using Serilog.Core;
+using ZB.MOM.WW.OtOpcUa.Commons.Engines;
+using ZB.MOM.WW.OtOpcUa.Core.ScriptedAlarms;
+using ZB.MOM.WW.OtOpcUa.Core.VirtualTags;
+
+namespace ZB.MOM.WW.OtOpcUa.Core.Scripting;
+
+/// <summary>
+///     <see cref="IScriptRunner"/> over today's in-process machinery: a <see cref="CompiledScriptCache{TContext, TResult}"/>
+///     per context kind and one <see cref="ScriptRunGuard"/> (lmxopcua#780, design §11). It produces the outcomes and
+///     reason strings the seams' own in-process paths produce, which makes it the parity baseline the out-of-process
+///     runner is tested against, and the in-process half of the future shadow mode (P2).
+/// </summary>
+/// <remarks>
+///     The seams do not route their <see cref="ScriptRunnerMode.InProcess"/> path through this class: they keep their
+///     existing guard code, so the default mode is unchanged byte for byte. Unlike those paths, this runner remembers
+///     compile failures by source for every kind (Calculation already did, R07:P4).
+/// </remarks>
+public sealed class InProcessScriptRunner : IScriptRunner, IDisposable
+{
+    private readonly CompiledScriptCache<VirtualTagContext, object?> _valueCache = new();
+    private readonly CompiledScriptCache<AlarmPredicateContext, bool> _predicateCache = new();
+    private readonly ConcurrentDictionary<string, string> _compileFailures = new(StringComparer.Ordinal);
+    private readonly ScriptRunGuard _guard;
+
+    /// <summary>Initializes the runner.</summary>
+    /// <param name="scripting">Run-guard knobs; null ⇒ defaults.</param>
+    /// <param name="logger">Where quarantine lines go; null ⇒ Serilog's global logger.</param>
+    public InProcessScriptRunner(ScriptingOptions? scripting = null, ILogger? logger = null)
+    {
+        _guard = new ScriptRunGuard(scripting, logger);
+    }
+
+    /// <summary>The run guard (diagnostics / tests).</summary>
+    public ScriptRunGuard RunGuard => _guard;
+
+    /// <inheritdoc />
+    public async Task<ScriptRunOutcome> RunAsync(ScriptInvocation invocation, CancellationToken ct = default)
+    {
+        ArgumentNullException.ThrowIfNull(invocation);
+        var key = ScopedKey(invocation.Kind, invocation.Key);
+        var failureKey = ScopedKey(invocation.Kind, invocation.Source);
+        if (_compileFailures.TryGetValue(failureKey, out var known)) return ScriptRunOutcome.Failed(known);
+        var logger = invocation.ScriptLogger ?? Logger.None;
+
+        try
+        {
+            switch (invocation.Kind)
+            {
+                case ScriptContextKind.VirtualTag:
+                case ScriptContextKind.Calculation:
+                {
+                    var evaluator = await Task.Run(() => _valueCache.GetOrCompile(invocation.Source), ct).ConfigureAwait(false);
+                    var context = new VirtualTagContext(invocation.Inputs, static (_, _) => { }, logger);
+                    var value = await _guard.RunAsync(key, invocation.Source, evaluator, context, invocation.Timeout, ct)
+                        .ConfigureAwait(false);
+                    return ScriptRunOutcome.Ok(value);
+                }
+                case ScriptContextKind.AlarmPredicate:
+                {
+                    var evaluator = await Task.Run(() => _predicateCache.GetOrCompile(invocation.Source), ct).ConfigureAwait(false);
+                    var context = new AlarmPredicateContext(invocation.Inputs, logger);
+                    var value = await _guard.RunAsync(key, invocation.Source, evaluator, context, invocation.Timeout, ct)
+                        .ConfigureAwait(false);
+                    return ScriptRunOutcome.Ok(value);
+                }
+                default:
+                    return ScriptRunOutcome.Failed($"unsupported script kind {invocation.Kind}");
+            }
+        }
+        catch (CompilationErrorException ex)
+        {
+            return RememberCompileFailure(failureKey, $"compile error: {ex.Message}");
+        }
+        catch (ScriptSandboxViolationException ex)
+        {
+            return RememberCompileFailure(failureKey, $"sandbox violation: {ex.Message}");
+        }
+        catch (ScriptTimeoutException)
+        {
+            return ScriptRunOutcome.Failed($"{ScriptEvalFailureReasons.TimedOutPrefix}{invocation.Timeout.TotalSeconds:F1}s");
+        }
+        catch (ScriptRunRefusedException ex)
+        {
+            return ScriptRunOutcome.Failed(ex.Message);
+        }
+        catch (ScriptQuarantinedException ex)
+        {
+            return ScriptRunOutcome.Failed(ex.Message);
+        }
+        catch (OperationCanceledException) when (ct.IsCancellationRequested)
+        {
+            return ScriptRunOutcome.Failed("evaluation cancelled");
+        }
+        catch (Exception ex)
+        {
+            return ScriptRunOutcome.Failed($"script threw: {ex.Message}");
+        }
+    }
+
+    /// <inheritdoc />
+    public void Reset(ScriptContextKind kind)
+    {
+        var prefix = ScopedKey(kind, string.Empty);
+        foreach (var k in _compileFailures.Keys)
+            if (k.StartsWith(prefix, StringComparison.Ordinal)) _compileFailures.TryRemove(k, out _);
+        foreach (var k in _guard.QuarantinedKeys)
+            if (k.StartsWith(prefix, StringComparison.Ordinal)) _guard.Reset(k);
+    }
+
+    /// <inheritdoc />
+    public IReadOnlyCollection<string> QuarantinedKeys(ScriptContextKind kind)
+    {
+        var prefix = ScopedKey(kind, string.Empty);
+        return _guard.QuarantinedKeys
+            .Where(k => k.StartsWith(prefix, StringComparison.Ordinal))
+            .Select(k => k[prefix.Length..])
+            .ToArray();
+    }
+
+    /// <inheritdoc />
+    public void Dispose()
+    {
+        _valueCache.Dispose();
+        _predicateCache.Dispose();
+    }
+
+    /// <summary>The runner-internal key: <c>{kind}:{key}</c>.</summary>
+    /// <param name="kind">The context kind.</param>
+    /// <param name="key">The seam's key.</param>
+    /// <returns>The namespaced key.</returns>
+    public static string ScopedKey(ScriptContextKind kind, string key) => $"{(int)kind}:{key}";
+
+    private ScriptRunOutcome RememberCompileFailure(string failureKey, string reason)
+    {
+        _compileFailures.TryAdd(failureKey, reason);
+        return ScriptRunOutcome.Failed(reason);
+    }
+}

src/Core/ZB.MOM.WW.OtOpcUa.Core.Scripting/ScriptRunnerOptions.cs

@@ -0,0 +1,213 @@
+namespace ZB.MOM.WW.OtOpcUa.Core.Scripting;
+
+/// <summary>
+///     Where compiled scripts run (<c>Scripting:Runner</c>, lmxopcua#780). <see cref="InProcess"/> is the default
+///     and the documented rollback: it is today's <see cref="ScriptRunGuard"/> path, unchanged.
+/// </summary>
+public enum ScriptRunnerMode
+{
+    /// <summary>Compiled scripts run in the host process under <see cref="ScriptRunGuard"/> (the default).</summary>
+    InProcess = 0,
+
+    /// <summary>
+    ///     Run in process AND submit to the worker, comparing the two (design P2). Not implemented yet: a node
+    ///     configured for it runs <see cref="InProcess"/> and logs a startup Warning.
+    /// </summary>
+    Shadow = 1,
+
+    /// <summary>
+    ///     Compiled scripts of the selected seams run in the pre-emptible <c>ScriptWorker</c> process pool. The
+    ///     runner fails closed: a worker that cannot start makes the script Bad
+    ///     (<c>BadResourceUnavailable</c>), never an in-process run.
+    /// </summary>
+    OutOfProcess = 2,
+}
+
+/// <summary>The three host seams that run operator-authored C# (<c>Scripting:Runner:Seams</c>).</summary>
+public enum ScriptSeam
+{
+    /// <summary>Virtual tags (<c>RoslynVirtualTagEvaluator</c>).</summary>
+    VirtualTag = 0,
+
+    /// <summary>Calculation tags (<c>CalculationEvaluator</c>).</summary>
+    Calculation = 1,
+
+    /// <summary>Scripted-alarm predicates (<c>ScriptedAlarmEngine</c>). Last in the rollout (design §14 #10).</summary>
+    ScriptedAlarm = 2,
+}
+
+/// <summary>
+///     The out-of-process worker pool's knobs (the <c>Scripting:Worker</c> section). Every value is clamped by
+///     <see cref="Sanitized"/>, which reports each out-of-range key as a startup Warning, like the rest of the
+///     <c>Scripting</c> section. Only consulted when <see cref="ScriptingOptions.Runner"/> is not
+///     <see cref="ScriptRunnerMode.InProcess"/>.
+/// </summary>
+public sealed class ScriptWorkerOptions
+{
+    /// <summary>Default <see cref="Shards"/>: 2 (design §14 #1).</summary>
+    public const int DefaultShards = 2;
+
+    /// <summary>Upper bound of <see cref="Shards"/>.</summary>
+    public const int MaxShards = 8;
+
+    /// <summary>Default <see cref="HeapLimitBytes"/>: 512 MiB.</summary>
+    public const long DefaultHeapLimitBytes = 512L * 1024 * 1024;
+
+    /// <summary>Lower bound of <see cref="HeapLimitBytes"/>: 64 MiB (a worker below this cannot host Roslyn).</summary>
+    public const long MinHeapLimitBytes = 64L * 1024 * 1024;
+
+    /// <summary>Default <see cref="QuarantineAfterKills"/>: 2.</summary>
+    public const int DefaultQuarantineAfterKills = 2;
+
+    /// <summary>Default <see cref="UnavailableGrace"/>: 5 s.</summary>
+    public static readonly TimeSpan DefaultUnavailableGrace = TimeSpan.FromSeconds(5);
+
+    /// <summary>Lower bound of an explicit <see cref="HardGrace"/>: 250 ms.</summary>
+    public static readonly TimeSpan MinHardGrace = TimeSpan.FromMilliseconds(250);
+
+    /// <summary>Upper bound of an explicit <see cref="HardGrace"/>: 30 s.</summary>
+    public static readonly TimeSpan MaxHardGrace = TimeSpan.FromSeconds(30);
+
+    /// <summary>Upper bound of <see cref="UnavailableGrace"/>: 60 s.</summary>
+    public static readonly TimeSpan MaxUnavailableGrace = TimeSpan.FromSeconds(60);
+
+    /// <summary>Default <see cref="IsolationProbationRuns"/>: 20.</summary>
+    public const int DefaultIsolationProbationRuns = 20;
+
+    /// <summary>Shard workers per node; a script is placed by a stable hash of its key. Clamped to 1–8.</summary>
+    public int Shards { get; set; } = DefaultShards;
+
+    /// <summary>
+    ///     Grace after the soft deadline <c>T</c> before the worker running the script is killed. Null (the default)
+    ///     means <c>max(1 s, T)</c> per run (design §14 #2); an explicit value is clamped to 250 ms – 30 s.
+    /// </summary>
+    public TimeSpan? HardGrace { get; set; }
+
+    /// <summary>The worker's <c>DOTNET_GCHeapHardLimit</c>. Default 512 MiB, minimum 64 MiB.</summary>
+    public long HeapLimitBytes { get; set; } = DefaultHeapLimitBytes;
+
+    /// <summary>Hard-deadline kills (within one hour) after which a script is quarantined. Default 2; 1–100.</summary>
+    public int QuarantineAfterKills { get; set; } = DefaultQuarantineAfterKills;
+
+    /// <summary>
+    ///     How long an evaluation waits for its shard to become ready (a restart, a backoff) before it reports
+    ///     <c>script runner unavailable</c>. Default 5 s; 0–60 s.
+    /// </summary>
+    public TimeSpan UnavailableGrace { get; set; } = DefaultUnavailableGrace;
+
+    /// <summary>
+    ///     Successful runs a suspect script must complete in the isolation worker before it returns to its shard.
+    ///     Default 20; 1–10 000.
+    /// </summary>
+    public int IsolationProbationRuns { get; set; } = DefaultIsolationProbationRuns;
+
+    /// <summary>
+    ///     Directory of the node-local compiled-PE cache (design §7). Must be absolute and outside the content root
+    ///     when set; startup fails otherwise (the family's fail-closed path rule). Reserved: the cache itself has
+    ///     not landed yet (lmxopcua#780 P1 remainder), so a worker restart recompiles.
+    /// </summary>
+    public string? PeCacheDir { get; set; }
+
+    /// <summary>
+    ///     Path of the worker entry assembly (<c>ZB.MOM.WW.OtOpcUa.ScriptWorker.dll</c>). Null (the default) means
+    ///     <c>script-worker/</c> under the host's base directory, where the Host build places it.
+    /// </summary>
+    public string? ExecutablePath { get; set; }
+
+    /// <summary>The hard grace that applies to a run with soft budget <paramref name="softTimeout"/>.</summary>
+    /// <param name="softTimeout">The run's soft deadline <c>T</c>.</param>
+    /// <returns><see cref="HardGrace"/> when set, otherwise <c>max(1 s, T)</c>.</returns>
+    public TimeSpan EffectiveHardGrace(TimeSpan softTimeout)
+        => HardGrace ?? (softTimeout > TimeSpan.FromSeconds(1) ? softTimeout : TimeSpan.FromSeconds(1));
+
+    /// <summary>Returns a clamped copy; one line per out-of-range key in <paramref name="adjustments"/>.</summary>
+    /// <param name="adjustments">The clamps applied, naming each key.</param>
+    /// <returns>A new, clamped instance.</returns>
+    public ScriptWorkerOptions Sanitized(out IReadOnlyList<string> adjustments)
+    {
+        const string prefix = ScriptingOptions.SectionName + ":Worker:";
+        var notes = new List<string>();
+
+        var shards = Shards;
+        if (shards < 1 || shards > MaxShards)
+        {
+            var clamped = Math.Clamp(shards, 1, MaxShards);
+            notes.Add($"{prefix}{nameof(Shards)} {shards} is outside 1–{MaxShards}; clamped to {clamped}.");
+            shards = clamped;
+        }
+
+        var grace = HardGrace;
+        if (grace is { } g && (g < MinHardGrace || g > MaxHardGrace))
+        {
+            var clamped = g < MinHardGrace ? MinHardGrace : MaxHardGrace;
+            notes.Add($"{prefix}{nameof(HardGrace)} {g} is outside {MinHardGrace}–{MaxHardGrace}; clamped to {clamped}.");
+            grace = clamped;
+        }
+
+        var heap = HeapLimitBytes;
+        if (heap < MinHeapLimitBytes)
+        {
+            notes.Add($"{prefix}{nameof(HeapLimitBytes)} {heap} is below the minimum; clamped to {MinHeapLimitBytes}.");
+            heap = MinHeapLimitBytes;
+        }
+
+        var kills = QuarantineAfterKills;
+        if (kills < 1 || kills > 100)
+        {
+            var clamped = Math.Clamp(kills, 1, 100);
+            notes.Add($"{prefix}{nameof(QuarantineAfterKills)} {kills} is outside 1–100; clamped to {clamped}.");
+            kills = clamped;
+        }
+
+        var unavailable = UnavailableGrace;
+        if (unavailable < TimeSpan.Zero || unavailable > MaxUnavailableGrace)
+        {
+            var clamped = unavailable < TimeSpan.Zero ? TimeSpan.Zero : MaxUnavailableGrace;
+            notes.Add($"{prefix}{nameof(UnavailableGrace)} {unavailable} is outside 0–{MaxUnavailableGrace}; clamped to {clamped}.");
+            unavailable = clamped;
+        }
+
+        var probation = IsolationProbationRuns;
+        if (probation < 1 || probation > 10_000)
+        {
+            var clamped = Math.Clamp(probation, 1, 10_000);
+            notes.Add($"{prefix}{nameof(IsolationProbationRuns)} {probation} is outside 1–10000; clamped to {clamped}.");
+            probation = clamped;
+        }
+
+        adjustments = notes;
+        return new ScriptWorkerOptions
+        {
+            Shards = shards,
+            HardGrace = grace,
+            HeapLimitBytes = heap,
+            QuarantineAfterKills = kills,
+            UnavailableGrace = unavailable,
+            IsolationProbationRuns = probation,
+            PeCacheDir = PeCacheDir,
+            ExecutablePath = ExecutablePath,
+        };
+    }
+
+    /// <summary>
+    ///     Fail-closed path validation (design §7): <see cref="PeCacheDir"/>, when set, must be absolute and must not
+    ///     sit inside <paramref name="contentRootPath"/>. Same rule as the family's <c>Secrets:SqlitePath</c>.
+    /// </summary>
+    /// <param name="contentRootPath">The host's content root.</param>
+    /// <returns>The violation, or null when the options are acceptable.</returns>
+    public string? ValidatePaths(string contentRootPath)
+    {
+        if (string.IsNullOrWhiteSpace(PeCacheDir)) return null;
+        const string key = ScriptingOptions.SectionName + ":Worker:" + nameof(PeCacheDir);
+        if (!Path.IsPathFullyQualified(PeCacheDir))
+            return $"{key} '{PeCacheDir}' must be an absolute path.";
+        var dir = Path.TrimEndingDirectorySeparator(Path.GetFullPath(PeCacheDir));
+        var root = Path.TrimEndingDirectorySeparator(Path.GetFullPath(contentRootPath));
+        var comparison = OperatingSystem.IsWindows() ? StringComparison.OrdinalIgnoreCase : StringComparison.Ordinal;
+        if (string.Equals(dir, root, comparison)
+            || dir.StartsWith(root + Path.DirectorySeparatorChar, comparison)
+            || dir.StartsWith(root + Path.AltDirectorySeparatorChar, comparison))
+            return $"{key} '{PeCacheDir}' is inside the content root '{contentRootPath}'; it must live outside it.";
+        return null;
+    }
+}

src/Core/ZB.MOM.WW.OtOpcUa.Core.Scripting/ScriptingOptions.cs

@@ -72,6 +72,30 @@ public sealed class ScriptingOptions
     /// </summary>
     public double StuckOrphanQuarantineFactor { get; set; } = DefaultStuckOrphanQuarantineFactor;
 
+    /// <summary>
+    ///     Where compiled scripts run (<c>Scripting:Runner</c>, lmxopcua#780). Default
+    ///     <see cref="ScriptRunnerMode.InProcess"/> — today's path, unchanged, and the rollback for the other modes.
+    /// </summary>
+    public ScriptRunnerMode Runner { get; set; } = ScriptRunnerMode.InProcess;
+
+    /// <summary>
+    ///     The seams <see cref="Runner"/> applies to when it is not <see cref="ScriptRunnerMode.InProcess"/>
+    ///     (<c>Scripting:Runner:Seams</c>, e.g. <c>["Calculation"]</c>). Null or empty means all three. Bound by
+    ///     <c>ScriptingOptionsBinding</c> from the documented key, because <c>Scripting:Runner</c> is itself a value.
+    /// </summary>
+    public IReadOnlyList<ScriptSeam>? RunnerSeams { get; set; }
+
+    /// <summary>The out-of-process worker pool's knobs (<c>Scripting:Worker</c>).</summary>
+    public ScriptWorkerOptions Worker { get; set; } = new();
+
+    /// <summary>Whether <paramref name="seam"/> is selected for out-of-process execution by these options.</summary>
+    /// <param name="seam">The seam.</param>
+    /// <returns><c>true</c> when <see cref="Runner"/> is <see cref="ScriptRunnerMode.OutOfProcess"/> and the seam is in
+    /// <see cref="RunnerSeams"/> (or that list is empty).</returns>
+    public bool IsOutOfProcess(ScriptSeam seam)
+        => Runner == ScriptRunnerMode.OutOfProcess
+           && (RunnerSeams is not { Count: > 0 } seams || seams.Contains(seam));
+
     /// <summary>Upper bound <see cref="Sanitized"/> applies to <see cref="StuckOrphanQuarantineFactor"/>.</summary>
     public const double MaxStuckOrphanQuarantineFactor = 1000;
 
@@ -158,6 +182,9 @@ public sealed class ScriptingOptions
             runTimeout = MaxRunTimeout;
         }
 
+        var worker = (Worker ?? new ScriptWorkerOptions()).Sanitized(out var workerNotes);
+        notes.AddRange(workerNotes);
+
         adjustments = notes;
         return new ScriptingOptions
         {
@@ -165,6 +192,9 @@ public sealed class ScriptingOptions
             MaxAllocBytesPerRun = alloc,
             QuarantineAfterConsecutiveTimeouts = threshold,
             StuckOrphanQuarantineFactor = factor,
+            Runner = Runner,
+            RunnerSeams = RunnerSeams is null ? null : [.. RunnerSeams],
+            Worker = worker,
         };
     }
 }

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/CalculationDriver.cs

@@ -137,7 +137,7 @@ public sealed class CalculationDriver : IDriver, IDependencyConsumer, ISubscriba
         // _logger (ILogger<CalculationDriver>) implements the non-generic ILogger, so it is passed straight
         // through — the evaluator's host-side diagnostics (compile errors, sandbox violations, execution
         // throws) land on the SAME logger the driver itself was constructed with, not a separate one.
-        _evaluator = new CalculationEvaluator(_logger, _scriptRoot, _options.RunTimeout, _options.Scripting);
+        _evaluator = new CalculationEvaluator(_logger, _scriptRoot, _options.RunTimeout, _options.Scripting, _options.ScriptRunner);
 
         RebuildTagTable(_options);
     }
@@ -639,7 +639,7 @@ public sealed class CalculationDriver : IDriver, IDependencyConsumer, ISubscriba
             if (!result.Success)
             {
                 var reason = result.Reason ?? "evaluator failure";
-                toPublish = MarkEvaluationFailed(st, pending.TimestampUtc);
+                toPublish = MarkEvaluationFailed(st, pending.TimestampUtc, result.StatusCode ?? StatusBadInternalError);
                 // The script-log entry fires on the Good→Bad TRANSITION, or when the failure changes
                 // (R07:P4) — not on every trigger of a tag that is already Bad for the same reason, which
                 // flooded the script log at the input's cadence. The Bad publish was already once per
@@ -725,16 +725,19 @@ public sealed class CalculationDriver : IDriver, IDependencyConsumer, ISubscriba
     /// returns before the evaluator ever runs), so there is no separate "inputs ready" condition here.</summary>
     /// <param name="st">The tag's published state.</param>
     /// <param name="timestampUtc">The trigger's timestamp.</param>
+    /// <param name="badStatus">The Bad code to publish (see the body).</param>
     /// <returns>The Bad snapshot to publish on a fresh Good→Bad transition, else null.</returns>
-    private static (object? Value, uint StatusCode)? MarkEvaluationFailed(TagState st, DateTime timestampUtc)
+    private static (object? Value, uint StatusCode)? MarkEvaluationFailed(TagState st, DateTime timestampUtc, uint badStatus)
     {
-        if (st.HasPublished && st.LastPublishedStatus == StatusBadInternalError) return null;
+        // badStatus is BadInternalError for every script failure; BadResourceUnavailable when the out-of-process
+        // runner could not run the script (lmxopcua#780). Once per transition, keyed on that code.
+        if (st.HasPublished && st.LastPublishedStatus == badStatus) return null;
 
         st.HasPublished = true;
-        st.LastPublishedStatus = StatusBadInternalError;
+        st.LastPublishedStatus = badStatus;
         st.LastTimestampUtc = timestampUtc;
         // Carry the last-known value (null if none) with Bad quality.
-        return (st.HasValue ? st.LastValue : null, StatusBadInternalError);
+        return (st.HasValue ? st.LastValue : null, badStatus);
     }
 
     private void Publish(string rawPath, object? value, uint statusCode, DateTime timestampUtc)

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/CalculationDriverFactoryExtensions.cs

@@ -40,14 +40,17 @@ public static class CalculationDriverFactoryExtensions
     /// <param name="scriptRoot">Optional root script logger (fans failure entries onto the <c>script-logs</c> topic).</param>
     /// <param name="scripting">The node-wide <c>Scripting</c> options every Calculation driver inherits; a key
     /// authored in a driver's own config overrides that one knob. Null ⇒ the compiled defaults.</param>
+    /// <param name="scriptRunner">lmxopcua#780 — the node's out-of-process runner when the Calculation seam runs out
+    /// of process; null (the default) keeps every driver on the in-process guard.</param>
     public static void Register(
         DriverFactoryRegistry registry,
         ILoggerFactory? loggerFactory = null,
         ScriptRootLogger? scriptRoot = null,
-        ScriptingOptions? scripting = null)
+        ScriptingOptions? scripting = null,
+        IScriptRunner? scriptRunner = null)
     {
         ArgumentNullException.ThrowIfNull(registry);
-        registry.Register(DriverTypeName, (id, json) => CreateInstance(id, json, loggerFactory, scriptRoot, scripting));
+        registry.Register(DriverTypeName, (id, json) => CreateInstance(id, json, loggerFactory, scriptRoot, scripting, scriptRunner));
     }
 
     /// <summary>Public overload for the Server-side bootstrapper + test consumers.</summary>
@@ -74,10 +77,12 @@ public static class CalculationDriverFactoryExtensions
     /// <param name="loggerFactory">Optional logger factory for per-instance diagnostics loggers.</param>
     /// <param name="scriptRoot">Optional root script logger for failure fan-out.</param>
     /// <param name="nodeScripting">The node-wide run-guard options; null ⇒ the compiled defaults.</param>
+    /// <param name="scriptRunner">The node's out-of-process runner, or null for in process.</param>
     /// <returns>The constructed <see cref="CalculationDriver"/>.</returns>
     public static CalculationDriver CreateInstance(
         string driverInstanceId, string driverConfigJson,
-        ILoggerFactory? loggerFactory, ScriptRootLogger? scriptRoot, ScriptingOptions? nodeScripting)
+        ILoggerFactory? loggerFactory, ScriptRootLogger? scriptRoot, ScriptingOptions? nodeScripting,
+        IScriptRunner? scriptRunner = null)
     {
         ArgumentException.ThrowIfNullOrWhiteSpace(driverInstanceId);
         ArgumentException.ThrowIfNullOrWhiteSpace(driverConfigJson);
@@ -101,6 +106,7 @@ public static class CalculationDriverFactoryExtensions
             RunTimeout = dto.RunTimeoutMs is { } ms && ms > 0
                 ? TimeSpan.FromMilliseconds(ms) : TimeSpan.FromSeconds(2),
             Scripting = scripting,
+            ScriptRunner = scriptRunner,
         };
 
         return new CalculationDriver(options, driverInstanceId, scriptRoot, logger: logger);

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/CalculationDriverOptions.cs

@@ -18,4 +18,11 @@ public sealed class CalculationDriverOptions
     ///     <see cref="ScriptingOptions"/> defaults (64 MB, 3).
     /// </summary>
     public ScriptingOptions? Scripting { get; init; }
+
+    /// <summary>
+    ///     lmxopcua#780 — the node's out-of-process runner when <c>Scripting:Runner=OutOfProcess</c> selects the
+    ///     Calculation seam; null (the default) keeps the in-process run guard. Shared by every Calculation driver on the
+    ///     node; keys are the calc tags' RawPaths.
+    /// </summary>
+    public IScriptRunner? ScriptRunner { get; init; }
 }

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/CalculationEvaluator.cs

@@ -59,6 +59,7 @@ public sealed class CalculationEvaluator : IScriptCacheOwner, IScriptQuarantineO
     private readonly SerilogLogger _scriptRoot;
     private readonly TimeSpan _runTimeout;
     private readonly ScriptRunGuard _guard;
+    private readonly IScriptRunner? _runner;
 
     // Negative compile cache (R07:P4), keyed by source hash. A compile error is a property of the SOURCE,
     // which never changes between triggers (it is fixed in the deploy artifact) — yet every trigger of a
@@ -76,12 +77,16 @@ public sealed class CalculationEvaluator : IScriptCacheOwner, IScriptQuarantineO
     /// <param name="scriptRoot">Root script logger; user <c>ctx.Logger.*</c> output flows through this to the Script-log page.</param>
     /// <param name="runTimeout">Wall-clock budget per script run; defaults to 2 seconds (parity with the VT evaluator).</param>
     /// <param name="scripting">Run-guard budget + quarantine threshold; null ⇒ <see cref="ScriptingOptions"/> defaults.</param>
+    /// <param name="scriptRunner">lmxopcua#780 — the out-of-process runner when the Calculation seam runs out of
+    /// process; null (the default) keeps the in-process guard path, unchanged.</param>
     public CalculationEvaluator(
         ILogger logger,
         ScriptRootLogger scriptRoot,
         TimeSpan? runTimeout = null,
-        ScriptingOptions? scripting = null)
+        ScriptingOptions? scripting = null,
+        IScriptRunner? scriptRunner = null)
     {
+        _runner = scriptRunner;
         _logger = logger ?? throw new ArgumentNullException(nameof(logger));
         _scriptRoot = (scriptRoot ?? throw new ArgumentNullException(nameof(scriptRoot))).Logger;
         _runTimeout = runTimeout ?? TimeSpan.FromSeconds(2);
@@ -188,6 +193,15 @@ public sealed class CalculationEvaluator : IScriptCacheOwner, IScriptQuarantineO
                     calcTagId, path),
             logger: scriptLog);
 
+        // lmxopcua#780 — OutOfProcess: the pre-emptible worker pool compiles and runs it, and owns timeouts, kills,
+        // quarantine and the negative compile cache for this seam. Unavailable publishes BadResourceUnavailable.
+        if (_runner is not null)
+        {
+            var outcome = await _runner.RunAsync(new ScriptInvocation(
+                calcTagId, ScriptContextKind.Calculation, scriptSource, readCache, _runTimeout, scriptLog), ct).ConfigureAwait(false);
+            return outcome.ToVirtualTagEvalResult();
+        }
+
         // A source that already failed to compile fails the same way without touching Roslyn (R07:P4).
         var sourceKey = HashSource(scriptSource);
         if (_compileFailures.TryGetValue(sourceKey, out var knownFailure))
@@ -295,13 +309,20 @@ public sealed class CalculationEvaluator : IScriptCacheOwner, IScriptQuarantineO
         // The compile-cache clear is this evaluator's deploy boundary — a redeploy lifts every quarantine
         // (an edited source already lifts its own through the guard's source identity).
         _guard.ResetAll();
+        _runner?.Reset(ScriptContextKind.Calculation);
     }
 
     /// <inheritdoc />
-    public void ResetQuarantines() => _guard.ResetAll();
+    public void ResetQuarantines()
+    {
+        _guard.ResetAll();
+        _runner?.Reset(ScriptContextKind.Calculation);
+    }
 
     /// <inheritdoc />
-    public IReadOnlyCollection<string> QuarantinedScripts => _guard.QuarantinedKeys;
+    public IReadOnlyCollection<string> QuarantinedScripts => _runner is null
+        ? _guard.QuarantinedKeys
+        : [.. _guard.QuarantinedKeys, .. _runner.QuarantinedKeys(ScriptContextKind.Calculation)];
 
     /// <summary>Disposes the evaluator, draining + disposing every cached compile's collectible ALC.</summary>
     public void Dispose()

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/ZB.MOM.WW.OtOpcUa.Driver.Calculation.csproj

@@ -30,6 +30,8 @@
 
     <ItemGroup>
         <InternalsVisibleTo Include="ZB.MOM.WW.OtOpcUa.Driver.Calculation.Tests"/>
+        <!-- lmxopcua#780: the worker suite drives a real driver over the real ScriptWorker (IsEvaluationIdle). -->
+        <InternalsVisibleTo Include="ZB.MOM.WW.OtOpcUa.ScriptWorker.Tests"/>
     </ItemGroup>
 
 </Project>

src/Server/ZB.MOM.WW.OtOpcUa.Host/Configuration/ScriptRunnerSelection.cs

@@ -0,0 +1,94 @@
+using ZB.MOM.WW.OtOpcUa.Core.Scripting;
+using ZB.MOM.WW.OtOpcUa.Core.Scripting.OutOfProcess;
+using SerilogLogger = Serilog.ILogger;
+
+namespace ZB.MOM.WW.OtOpcUa.Host.Configuration;
+
+/// <summary>
+///     Which <see cref="IScriptRunner"/> each script seam uses on this node (lmxopcua#780, <c>Scripting:Runner</c>). Under
+///     the <see cref="ScriptRunnerMode.InProcess"/> default every seam gets null and keeps its in-process guard path,
+///     unchanged. Under <see cref="ScriptRunnerMode.OutOfProcess"/> the selected seams share one
+///     <see cref="OutOfProcessScriptRunner"/>, which starts no worker until the first compiled evaluation, so a node with
+///     no scripts (or an admin-only node) never launches one. Disposed with the host's service provider, which stops the
+///     workers.
+/// </summary>
+public sealed class ScriptRunnerSelection : IAsyncDisposable, IDisposable
+{
+    /// <summary>Seams the out-of-process runner can serve in this build. Scripted alarms go last (design §14 #10).</summary>
+    public static readonly IReadOnlyList<ScriptSeam> SupportedOutOfProcessSeams = [ScriptSeam.VirtualTag, ScriptSeam.Calculation];
+
+    private readonly OutOfProcessScriptRunner? _runner;
+    private readonly HashSet<ScriptSeam> _seams;
+
+    private ScriptRunnerSelection(OutOfProcessScriptRunner? runner, IEnumerable<ScriptSeam> seams)
+    {
+        _runner = runner;
+        _seams = [.. seams];
+    }
+
+    /// <summary>The out-of-process runner, when one is configured.</summary>
+    public IScriptRunner? OutOfProcessRunner => _runner;
+
+    /// <summary>The runner <paramref name="seam"/> must use, or null for its in-process path.</summary>
+    /// <param name="seam">The seam.</param>
+    /// <returns>The runner, or null.</returns>
+    public IScriptRunner? ForSeam(ScriptSeam seam) => _runner is not null && _seams.Contains(seam) ? _runner : null;
+
+    /// <summary>
+    ///     Startup checks for the runner options: returns the Warnings to log, and throws when the configuration must
+    ///     not start (a <c>PeCacheDir</c> that is relative or inside the content root — fail closed).
+    /// </summary>
+    /// <param name="options">The bound, sanitized <c>Scripting</c> options.</param>
+    /// <param name="contentRootPath">The host's content root.</param>
+    /// <returns>Warnings for the caller to log.</returns>
+    /// <exception cref="InvalidOperationException">The worker path options are unacceptable.</exception>
+    public static IReadOnlyList<string> Validate(ScriptingOptions options, string contentRootPath)
+    {
+        ArgumentNullException.ThrowIfNull(options);
+        var warnings = new List<string>();
+        if (options.Runner == ScriptRunnerMode.InProcess) return warnings;
+
+        if (options.Worker.ValidatePaths(contentRootPath) is { } violation)
+            throw new InvalidOperationException($"Scripting misconfiguration: {violation}");
+
+        if (options.Runner == ScriptRunnerMode.Shadow)
+        {
+            warnings.Add("Scripting:Runner=Shadow is not implemented yet (lmxopcua#780 P2); every seam runs InProcess.");
+            return warnings;
+        }
+
+        foreach (var seam in RequestedSeams(options))
+        {
+            if (!SupportedOutOfProcessSeams.Contains(seam))
+                warnings.Add($"Scripting:Runner=OutOfProcess: the {seam} seam cannot run out of process yet (lmxopcua#780); it stays InProcess.");
+        }
+        var workerPath = OutOfProcessScriptRunner.ResolveWorkerPath(options.Worker);
+        if (!File.Exists(workerPath))
+            warnings.Add($"Scripting:Runner=OutOfProcess: the script worker '{workerPath}' does not exist; every out-of-process " +
+                         "script reports BadResourceUnavailable (the runner fails closed, it never falls back to in process).");
+        return warnings;
+    }
+
+    /// <summary>Builds the selection for <paramref name="options"/>.</summary>
+    /// <param name="options">The bound, sanitized <c>Scripting</c> options.</param>
+    /// <param name="log">Host diagnostics for the runner.</param>
+    /// <param name="scriptRoot">The root script logger forwarded <c>ctx.Logger</c> lines fall back to.</param>
+    /// <returns>The selection.</returns>
+    public static ScriptRunnerSelection Create(ScriptingOptions options, SerilogLogger log, SerilogLogger? scriptRoot)
+    {
+        ArgumentNullException.ThrowIfNull(options);
+        if (options.Runner != ScriptRunnerMode.OutOfProcess) return new ScriptRunnerSelection(null, []);
+        var seams = RequestedSeams(options).Where(SupportedOutOfProcessSeams.Contains).ToArray();
+        if (seams.Length == 0) return new ScriptRunnerSelection(null, []);
+        return new ScriptRunnerSelection(new OutOfProcessScriptRunner(options, log, scriptRoot), seams);
+    }
+
+    /// <inheritdoc />
+    public ValueTask DisposeAsync() => _runner?.DisposeAsync() ?? ValueTask.CompletedTask;
+
+    /// <inheritdoc />
+    public void Dispose() => _runner?.Dispose();
+
+    private static IEnumerable<ScriptSeam> RequestedSeams(ScriptingOptions options)
+        => options.RunnerSeams is { Count: > 0 } seams ? seams.Distinct() : Enum.GetValues<ScriptSeam>();
+}

src/Server/ZB.MOM.WW.OtOpcUa.Host/Configuration/ScriptingOptionsBinding.cs

@@ -18,6 +18,11 @@ public static class ScriptingOptionsBinding
     {
         ArgumentNullException.ThrowIfNull(configuration);
         var bound = configuration.GetSection(ScriptingOptions.SectionName).Get<ScriptingOptions>() ?? new ScriptingOptions();
+        // lmxopcua#780: the seam subset lives under the runner key (Scripting:Runner:Seams), which the binder cannot
+        // reach because Scripting:Runner is itself a value. Bound explicitly; an unknown seam name is a startup error,
+        // like an unknown Scripting:Runner value.
+        var seams = configuration.GetSection($"{ScriptingOptions.SectionName}:Runner:Seams").Get<List<ScriptSeam>>();
+        if (seams is { Count: > 0 }) bound.RunnerSeams = seams;
         return bound.Sanitized(out adjustments);
     }
 }

src/Server/ZB.MOM.WW.OtOpcUa.Host/Drivers/DriverFactoryBootstrap.cs

@@ -102,7 +102,10 @@ public static class DriverFactoryBootstrap
             // failures; without this it writes to NullLogger in production.
             ConfigureAbTransportLogging(sp);
             Register(registry, loggerFactory, secretResolver, primaryRoleSource, ResolveAbCipDefaultTransport(sp),
-                sp.GetRequiredService<Driver.Galaxy.Runtime.IGalaxyAckIdentityDirectory>(), scriptRoot, scripting);
+                sp.GetRequiredService<Driver.Galaxy.Runtime.IGalaxyAckIdentityDirectory>(), scriptRoot, scripting,
+                // lmxopcua#780: null under the InProcess default (and in test graphs that register no selection).
+                sp.GetService<ZB.MOM.WW.OtOpcUa.Host.Configuration.ScriptRunnerSelection>()
+                    ?.ForSeam(ZB.MOM.WW.OtOpcUa.Core.Scripting.ScriptSeam.Calculation));
             return registry;
         });
         services.AddSingleton<IDriverFactory>(sp =>
@@ -233,11 +236,12 @@ public static class DriverFactoryBootstrap
         Driver.AbCip.AbCipTransport abCipDefaultTransport,
         Driver.Galaxy.Runtime.IGalaxyAckIdentityDirectory galaxyAckIdentities,
         ZB.MOM.WW.OtOpcUa.Core.Scripting.ScriptRootLogger? scriptRoot = null,
-        ZB.MOM.WW.OtOpcUa.Core.Scripting.ScriptingOptions? scripting = null)
+        ZB.MOM.WW.OtOpcUa.Core.Scripting.ScriptingOptions? scripting = null,
+        ZB.MOM.WW.OtOpcUa.Core.Scripting.IScriptRunner? scriptRunner = null)
     {
         Driver.AbCip.AbCipDriverFactoryExtensions.Register(registry, loggerFactory, abCipDefaultTransport);
         Driver.AbLegacy.AbLegacyDriverFactoryExtensions.Register(registry, loggerFactory);
-        Driver.Calculation.CalculationDriverFactoryExtensions.Register(registry, loggerFactory, scriptRoot, scripting);
+        Driver.Calculation.CalculationDriverFactoryExtensions.Register(registry, loggerFactory, scriptRoot, scripting, scriptRunner);
         Driver.FOCAS.FocasDriverFactoryExtensions.Register(registry, loggerFactory);
         Driver.Galaxy.GalaxyDriverFactoryExtensions.Register(registry, secretResolver, loggerFactory, galaxyAckIdentities);
         Driver.Modbus.ModbusDriverFactoryExtensions.Register(registry, loggerFactory);

src/Server/ZB.MOM.WW.OtOpcUa.Host/Engines/RoslynVirtualTagEvaluator.cs

@@ -53,6 +53,7 @@ public sealed class RoslynVirtualTagEvaluator : IVirtualTagEvaluator, IScriptCac
     private readonly SerilogLogger _scriptRoot;
     private readonly TimeSpan _runTimeout;
     private readonly ScriptRunGuard _guard;
+    private readonly IScriptRunner? _runner;
     private bool _disposed;
 
     /// <summary>Initializes a new RoslynVirtualTagEvaluator with the given loggers and optional timeout.</summary>
@@ -61,18 +62,28 @@ public sealed class RoslynVirtualTagEvaluator : IVirtualTagEvaluator, IScriptCac
     /// <param name="runTimeout">Maximum execution time for each script; null ⇒ <see cref="ScriptingOptions.RunTimeout"/>
     /// of <paramref name="scripting"/> (2 s by default).</param>
     /// <param name="scripting">Run-guard budget + quarantine threshold (the <c>Scripting</c> section); null ⇒ defaults.</param>
+    /// <param name="scriptRunner">
+    ///     lmxopcua#780 — the out-of-process runner when <c>Scripting:Runner=OutOfProcess</c> selects the VirtualTag seam;
+    ///     null (the default, <c>InProcess</c>) keeps the in-process guard path below, unchanged. The passthrough fast path
+    ///     never reaches it.
+    /// </param>
     public RoslynVirtualTagEvaluator(
         ILogger<RoslynVirtualTagEvaluator> logger,
         ScriptRootLogger scriptRoot,
         TimeSpan? runTimeout = null,
-        ScriptingOptions? scripting = null)
+        ScriptingOptions? scripting = null,
+        IScriptRunner? scriptRunner = null)
     {
         _logger = logger;
         _scriptRoot = (scriptRoot ?? throw new ArgumentNullException(nameof(scriptRoot))).Logger;
         _runTimeout = runTimeout ?? (scripting ?? new ScriptingOptions()).Sanitized(out _).RunTimeout;
         _guard = new ScriptRunGuard(scripting, _scriptRoot);
+        _runner = scriptRunner;
     }
 
+    /// <summary>The out-of-process runner this evaluator delegates compiled runs to, or null (in process).</summary>
+    public IScriptRunner? ScriptRunner => _runner;
+
     /// <summary>The run guard every compiled evaluation goes through (diagnostics / tests).</summary>
     public ScriptRunGuard RunGuard => _guard;
 
@@ -147,6 +158,16 @@ public sealed class RoslynVirtualTagEvaluator : IVirtualTagEvaluator, IScriptCac
                     virtualTagId, path),
             logger: scriptLog);
 
+        // lmxopcua#780 — OutOfProcess: the compiled run goes to the pre-emptible worker pool, which compiles in the
+        // worker and owns timeouts, kills and quarantine for this seam. An Unavailable outcome (worker restarted, no
+        // worker ready) publishes BadResourceUnavailable; everything else keeps today's Bad contract.
+        if (_runner is not null)
+        {
+            var outcome = await _runner.RunAsync(new ScriptInvocation(
+                virtualTagId, ScriptContextKind.VirtualTag, expression, readCache, _runTimeout, scriptLog)).ConfigureAwait(false);
+            return outcome.ToVirtualTagEvalResult();
+        }
+
         // 02/S12: fetch + run inside a bounded loop so an ObjectDisposedException caused by a concurrent
         // apply-boundary ClearCompiledScripts (which disposed the evaluator between GetOrCompile and the
         // run's disposed guard) re-fetches and retries exactly once. The loop runs at most twice — the
@@ -235,13 +256,20 @@ public sealed class RoslynVirtualTagEvaluator : IVirtualTagEvaluator, IScriptCac
         // The compile-cache clear IS the deploy boundary for this evaluator: a redeploy lifts every quarantine
         // (an edited expression already lifts its own through the guard's source identity).
         _guard.ResetAll();
+        _runner?.Reset(ScriptContextKind.VirtualTag);
     }
 
     /// <inheritdoc />
-    public void ResetQuarantines() => _guard.ResetAll();
+    public void ResetQuarantines()
+    {
+        _guard.ResetAll();
+        _runner?.Reset(ScriptContextKind.VirtualTag);
+    }
 
     /// <inheritdoc />
-    public IReadOnlyCollection<string> QuarantinedScripts => _guard.QuarantinedKeys;
+    public IReadOnlyCollection<string> QuarantinedScripts => _runner is null
+        ? _guard.QuarantinedKeys
+        : [.. _guard.QuarantinedKeys, .. _runner.QuarantinedKeys(ScriptContextKind.VirtualTag)];
 
     /// <summary>Disposes the evaluator and cleans up all cached script evaluators.</summary>
     public void Dispose()

src/Server/ZB.MOM.WW.OtOpcUa.Host/Program.cs

@@ -376,6 +376,16 @@ if (hasDriver)
         Log.Warning("Scripting misconfiguration detected at startup: {Adjustment}", adjustment);
     builder.Services.AddSingleton(scriptingOptions);
 
+    // lmxopcua#780: Scripting:Runner (InProcess default / Shadow / OutOfProcess). Under the default every seam keeps its
+    // in-process guard path unchanged; OutOfProcess hands the selected seams' compiled runs to the pre-emptible
+    // ScriptWorker pool. A PeCacheDir that is relative or inside the content root stops startup (fail closed).
+    foreach (var warning in ZB.MOM.WW.OtOpcUa.Host.Configuration.ScriptRunnerSelection.Validate(
+                 scriptingOptions, builder.Environment.ContentRootPath))
+        Log.Warning("Scripting runner: {RunnerWarning}", warning);
+    Log.Information("Scripting runner: {RunnerMode}", scriptingOptions.Runner);
+    builder.Services.AddSingleton(sp => ZB.MOM.WW.OtOpcUa.Host.Configuration.ScriptRunnerSelection.Create(
+        sp.GetRequiredService<ScriptingOptions>(), Log.Logger, sp.GetService<ScriptRootLogger>()?.Logger));
+
     // lmxopcua#777: the ONE operator-write timeout (DriverWrites:Timeout) every write bound is derived from — the
     // driver child's cancel + abandon, its queue budget, DriverHostActor's Ask and the inbound-write gateway's Ask.
     // Checked against the resilience tiers' Write timeouts here; an inconsistency is a startup Warning (a tier
@@ -392,7 +402,9 @@ if (hasDriver)
         new RoslynVirtualTagEvaluator(
             sp.GetRequiredService<ILoggerFactory>().CreateLogger<RoslynVirtualTagEvaluator>(),
             sp.GetRequiredService<ScriptRootLogger>(),
-            scripting: sp.GetRequiredService<ScriptingOptions>()));
+            scripting: sp.GetRequiredService<ScriptingOptions>(),
+            scriptRunner: sp.GetRequiredService<ZB.MOM.WW.OtOpcUa.Host.Configuration.ScriptRunnerSelection>()
+                .ForSeam(ScriptSeam.VirtualTag)));
     builder.Services.AddSingleton<IVirtualTagEvaluator>(sp => sp.GetRequiredService<RoslynVirtualTagEvaluator>());
 
     // Script-log fan-out (Layer 0). The DPS publisher resolves the ActorSystem lazily so it never

src/Server/ZB.MOM.WW.OtOpcUa.Host/ZB.MOM.WW.OtOpcUa.Host.csproj

@@ -57,6 +57,7 @@
         <ProjectReference Include="..\..\Core\ZB.MOM.WW.OtOpcUa.Configuration\ZB.MOM.WW.OtOpcUa.Configuration.csproj"/>
         <ProjectReference Include="..\..\Core\ZB.MOM.WW.OtOpcUa.Core\ZB.MOM.WW.OtOpcUa.Core.csproj"/>
         <ProjectReference Include="..\..\Core\ZB.MOM.WW.OtOpcUa.Core.Scripting\ZB.MOM.WW.OtOpcUa.Core.Scripting.csproj"/>
+        <ProjectReference Include="..\..\Core\ZB.MOM.WW.OtOpcUa.Core.Scripting.OutOfProcess\ZB.MOM.WW.OtOpcUa.Core.Scripting.OutOfProcess.csproj"/>
         <ProjectReference Include="..\..\Core\ZB.MOM.WW.OtOpcUa.Core.VirtualTags\ZB.MOM.WW.OtOpcUa.Core.VirtualTags.csproj"/>
         <ProjectReference Include="..\..\Core\ZB.MOM.WW.OtOpcUa.Core.ScriptedAlarms\ZB.MOM.WW.OtOpcUa.Core.ScriptedAlarms.csproj"/>
         <ProjectReference Include="..\ZB.MOM.WW.OtOpcUa.Security\ZB.MOM.WW.OtOpcUa.Security.csproj"/>
@@ -90,4 +91,7 @@
         <ProjectReference Include="..\..\Drivers\ZB.MOM.WW.OtOpcUa.Driver.TwinCAT\ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.csproj"/>
     </ItemGroup>
 
+    <!-- lmxopcua#780: the out-of-process script runner's worker ships in script-worker/ beside the host. -->
+    <Import Project="..\ZB.MOM.WW.OtOpcUa.ScriptWorker\build\ScriptWorker.Deploy.targets"/>
+
 </Project>

src/Server/ZB.MOM.WW.OtOpcUa.Runtime/VirtualTags/VirtualTagActor.cs

@@ -391,7 +391,8 @@ public sealed class VirtualTagActor : ReceiveActor, IWithUnboundedStash
         var result = evaluation.Result;
         if (!result.Success)
         {
-            OnEvaluationFailed(result.Reason ?? "evaluator failure", "Warning", timestampUtc);
+            OnEvaluationFailed(result.Reason ?? "evaluator failure", "Warning", timestampUtc,
+                result.StatusCode ?? OpcUaStatus.BadInternalError);
             return;
         }
 
@@ -472,7 +473,10 @@ public sealed class VirtualTagActor : ReceiveActor, IWithUnboundedStash
     /// <param name="reason">The failure reason for the script-log entry.</param>
     /// <param name="level">The script-log level ("Warning" for a Failure result, "Error" for a throw).</param>
     /// <param name="timestampUtc">The triggering dependency change's timestamp, stamped on the Bad result.</param>
-    private void OnEvaluationFailed(string reason, string level, DateTime timestampUtc)
+    /// <param name="badStatus">The Bad code to publish: <see cref="OpcUaStatus.BadInternalError"/> for every script
+    /// failure, <see cref="OpcUaStatus.BadResourceUnavailable"/> when the out-of-process runner could not run the
+    /// script (lmxopcua#780). The once-per-transition dedup is on this code, so a switch between the two publishes.</param>
+    private void OnEvaluationFailed(string reason, string level, DateTime timestampUtc, uint badStatus = OpcUaStatus.BadInternalError)
     {
         OtOpcUaTelemetry.VirtualTagEval.Add(1, new KeyValuePair<string, object?>("outcome", "fail"));
 
@@ -488,15 +492,15 @@ public sealed class VirtualTagActor : ReceiveActor, IWithUnboundedStash
         }
         if (admission.Admitted) PublishLog(level, reason);
 
-        if ((_hasPublished && _lastPublishedStatus == OpcUaStatus.BadInternalError) || !AllDependenciesArrived())
+        if ((_hasPublished && _lastPublishedStatus == badStatus) || !AllDependenciesArrived())
         {
             return;
         }
 
         _hasPublished = true;
-        _lastPublishedStatus = OpcUaStatus.BadInternalError;
+        _lastPublishedStatus = badStatus;
         Context.Parent.Tell(new EvaluationResult(
-            _virtualTagId, _hasLastValue ? _lastValue : null, timestampUtc, CorrelationId.NewId(), OpcUaStatus.BadInternalError));
+            _virtualTagId, _hasLastValue ? _lastValue : null, timestampUtc, CorrelationId.NewId(), badStatus));
     }
 
     /// <summary>Inputs-ready gate (the retired cascade engine's rule): true once

src/Server/ZB.MOM.WW.OtOpcUa.ScriptWorker/Program.cs

@@ -0,0 +1,36 @@
+using System.IO.Pipes;
+using ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol;
+
+namespace ZB.MOM.WW.OtOpcUa.ScriptWorker;
+
+/// <summary>Entry point: connect to the host's pipe named in the environment and serve until told to stop.</summary>
+internal static class Program
+{
+    private static async Task<int> Main()
+    {
+        var pipeName = Environment.GetEnvironmentVariable(ScriptWorkerEnvironment.PipeName);
+        var nonce = Environment.GetEnvironmentVariable(ScriptWorkerEnvironment.Nonce);
+        if (string.IsNullOrEmpty(pipeName) || string.IsNullOrEmpty(nonce))
+        {
+            await Console.Error.WriteLineAsync("ScriptWorker: launched without a pipe name or nonce; exiting.");
+            return ScriptWorkerEnvironment.ExitProtocolFault;
+        }
+        _ = int.TryParse(Environment.GetEnvironmentVariable(ScriptWorkerEnvironment.ParentPid), out var parentPid);
+
+        // CurrentUserOnly: the client verifies the server end is owned by this account as well.
+        var pipe = new NamedPipeClientStream(".", pipeName, PipeDirection.InOut,
+            PipeOptions.Asynchronous | PipeOptions.CurrentUserOnly);
+        try
+        {
+            await pipe.ConnectAsync(TimeSpan.FromSeconds(10), CancellationToken.None);
+        }
+        catch (Exception ex)
+        {
+            await Console.Error.WriteLineAsync($"ScriptWorker: could not connect to the host pipe: {ex.Message}");
+            return ScriptWorkerEnvironment.ExitProtocolFault;
+        }
+
+        var host = new WorkerHost(pipe, nonce, parentPid);
+        return await host.RunAsync();
+    }
+}

src/Server/ZB.MOM.WW.OtOpcUa.ScriptWorker/WorkerHost.cs

@@ -0,0 +1,576 @@
+using System.Collections;
+using System.Collections.Concurrent;
+using System.Diagnostics;
+using System.IO.Pipes;
+using System.Threading.Channels;
+using Serilog;
+using Serilog.Core;
+using Serilog.Events;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Core.Scripting;
+using ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol;
+using ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol.V1;
+using ZB.MOM.WW.OtOpcUa.Core.ScriptedAlarms;
+using ZB.MOM.WW.OtOpcUa.Core.VirtualTags;
+
+namespace ZB.MOM.WW.OtOpcUa.ScriptWorker;
+
+/// <summary>
+///     One worker's whole life (lmxopcua#780, design §3.2): handshake, compile-on-load, a bounded evaluation scheduler
+///     on dedicated threads, a hard-deadline watchdog, heartbeats, and log forwarding. The host is authoritative for
+///     deadlines (it kills this process); the watchdog is the belt to that brace and fails fast slightly later, so the
+///     exit names the key that overran.
+/// </summary>
+/// <remarks>
+///     Anything that means "the host is gone" — pipe end of stream, a protocol fault, the parent pid disappearing —
+///     ends the process. The worker never outlives its host (design §3.3).
+/// </remarks>
+internal sealed class WorkerHost
+{
+    /// <summary>The watchdog fails fast this long after the host's own hard deadline, so the host normally wins.</summary>
+    private static readonly TimeSpan WatchdogMargin = TimeSpan.FromMilliseconds(500);
+
+    private readonly NamedPipeClientStream _pipe;
+    private readonly string _nonce;
+    private readonly int _parentPid;
+    private readonly Channel<Envelope> _outbound = Channel.CreateUnbounded<Envelope>(
+        new UnboundedChannelOptions { SingleReader = true });
+    private readonly ConcurrentDictionary<string, LoadedScript> _scripts = new(StringComparer.Ordinal);
+    private readonly ConcurrentDictionary<long, RunningEval> _running = new();
+    private readonly BlockingCollection<EvalRequest> _queue = new(new ConcurrentQueue<EvalRequest>());
+    private readonly ForwardingLogSink _logSink;
+    private readonly ILogger _scriptLogger;
+    private int _maxFrameBytes = ScriptWorkerFrameCodec.DefaultMaxFrameBytes;
+    private int _queueCapacity = 4096;
+    private TimeSpan _hardGrace = TimeSpan.FromSeconds(1);
+    private TimeSpan _heartbeatInterval = TimeSpan.FromSeconds(1);
+    private long _seq;
+
+    public WorkerHost(NamedPipeClientStream pipe, string nonce, int parentPid)
+    {
+        _pipe = pipe;
+        _nonce = nonce;
+        _parentPid = parentPid;
+        _logSink = new ForwardingLogSink();
+        _scriptLogger = new LoggerConfiguration().MinimumLevel.Verbose().WriteTo.Sink(_logSink).CreateLogger();
+    }
+
+    public async Task<int> RunAsync()
+    {
+        try
+        {
+            var hello = await ScriptWorkerFrameCodec.ReadAsync(_pipe, ScriptWorkerFrameCodec.DefaultMaxFrameBytes);
+            if (hello is null) return ScriptWorkerEnvironment.ExitPipeClosed;
+            if (hello.BodyCase != Envelope.BodyOneofCase.Hello)
+                throw new ScriptWorkerProtocolException($"expected Hello, got {hello.BodyCase}");
+            Configure(hello.Hello);
+
+            // The nonce is echoed, not trusted: the host compares it with the one it put in OUR environment, which
+            // proves the process on the other end of its pipe is the one it launched.
+            await ScriptWorkerFrameCodec.WriteAsync(_pipe, Wrap(new Envelope
+            {
+                Ready = new Ready
+                {
+                    Nonce = _nonce,
+                    Pid = Environment.ProcessId,
+                    RuntimeVersion = Environment.Version.ToString(),
+                },
+            }), _maxFrameBytes);
+
+            _logSink.Capacity = (int)Math.Max(1, hello.Hello.MaxLogLines == 0 ? 1000 : hello.Hello.MaxLogLines);
+            StartBackground(Math.Max(1, (int)hello.Hello.EvalThreads));
+            var writer = Task.Run(WriteLoopAsync);
+            var exit = await ReadLoopAsync();
+            _outbound.Writer.TryComplete();
+            try { await writer.WaitAsync(TimeSpan.FromSeconds(1)); } catch { /* exiting regardless */ }
+            return exit;
+        }
+        catch (ScriptWorkerProtocolException ex)
+        {
+            await Console.Error.WriteLineAsync($"ScriptWorker: protocol fault: {ex.Message}");
+            return ScriptWorkerEnvironment.ExitProtocolFault;
+        }
+        catch (IOException)
+        {
+            return ScriptWorkerEnvironment.ExitPipeClosed;
+        }
+    }
+
+    private void Configure(Hello hello)
+    {
+        if (hello.MaxFrameBytes > 0) _maxFrameBytes = (int)Math.Min(hello.MaxFrameBytes, 64u * 1024 * 1024);
+        if (hello.QueueCapacity > 0) _queueCapacity = (int)hello.QueueCapacity;
+        if (hello.HardGraceMs > 0) _hardGrace = TimeSpan.FromMilliseconds(hello.HardGraceMs);
+        if (hello.HeartbeatIntervalMs > 0) _heartbeatInterval = TimeSpan.FromMilliseconds(hello.HeartbeatIntervalMs);
+    }
+
+    private void StartBackground(int evalThreads)
+    {
+        for (var i = 0; i < evalThreads; i++)
+        {
+            new Thread(EvalThreadLoop) { IsBackground = true, Name = $"ScriptWorker.Eval{i}" }.Start();
+        }
+        new Thread(WatchdogLoop) { IsBackground = true, Name = "ScriptWorker.Watchdog" }.Start();
+        _ = Task.Run(HeartbeatLoopAsync);
+        _ = Task.Run(LogFlushLoopAsync);
+        if (_parentPid > 0) _ = Task.Run(ParentWatchLoopAsync);
+    }
+
+    private async Task<int> ReadLoopAsync()
+    {
+        while (true)
+        {
+            Envelope? frame;
+            try
+            {
+                frame = await ScriptWorkerFrameCodec.ReadAsync(_pipe, _maxFrameBytes);
+            }
+            catch (ScriptWorkerProtocolException ex)
+            {
+                await Console.Error.WriteLineAsync($"ScriptWorker: protocol fault: {ex.Message}");
+                return ScriptWorkerEnvironment.ExitProtocolFault;
+            }
+            catch (IOException)
+            {
+                return ScriptWorkerEnvironment.ExitPipeClosed;
+            }
+            if (frame is null) return ScriptWorkerEnvironment.ExitPipeClosed; // host gone: fatal by design
+
+            switch (frame.BodyCase)
+            {
+                case Envelope.BodyOneofCase.Load:
+                {
+                    // Compile off the reader, so evaluations for already-loaded keys keep flowing during a load.
+                    var load = frame.Load;
+                    _ = Task.Run(() => Load(load));
+                    break;
+                }
+                case Envelope.BodyOneofCase.Unload:
+                    foreach (var key in frame.Unload.Keys)
+                        if (_scripts.TryRemove(key, out var gone)) gone.Dispose();
+                    break;
+                case Envelope.BodyOneofCase.Eval:
+                    foreach (var item in frame.Eval.Items) Admit(item);
+                    break;
+                case Envelope.BodyOneofCase.Cancel:
+                    if (_running.TryGetValue((long)frame.Cancel.EvalId, out var toCancel))
+                    {
+                        try { toCancel.Cancellation.Cancel(); } catch (ObjectDisposedException) { /* just finished */ }
+                    }
+                    break;
+                case Envelope.BodyOneofCase.DiagRequest:
+                    Send(new Envelope { DiagReply = Diagnostics() });
+                    break;
+                case Envelope.BodyOneofCase.Shutdown:
+                    return 0;
+                case Envelope.BodyOneofCase.Fault:
+                    await Console.Error.WriteLineAsync($"ScriptWorker: host fault: {frame.Fault.Message}");
+                    return ScriptWorkerEnvironment.ExitProtocolFault;
+                default:
+                    await Console.Error.WriteLineAsync($"ScriptWorker: unexpected frame {frame.BodyCase}");
+                    return ScriptWorkerEnvironment.ExitProtocolFault;
+            }
+        }
+    }
+
+    private void Load(LoadScripts load)
+    {
+        var result = new LoadResult { LoadId = load.LoadId };
+        foreach (var script in load.Scripts)
+        {
+            var outcome = new LoadOutcome { Key = script.Key, Ok = true };
+            try
+            {
+                var loaded = LoadedScript.Compile(script);
+                if (_scripts.TryRemove(script.Key, out var previous)) previous.Dispose();
+                _scripts[script.Key] = loaded;
+            }
+            catch (CompilationErrorException ex)
+            {
+                outcome.Ok = false;
+                outcome.Error = new ScriptError { Kind = ScriptError.Types.Kind.Compile, Message = ex.Message };
+            }
+            catch (ScriptSandboxViolationException ex)
+            {
+                outcome.Ok = false;
+                outcome.Error = new ScriptError { Kind = ScriptError.Types.Kind.Sandbox, Message = ex.Message };
+            }
+            catch (Exception ex)
+            {
+                outcome.Ok = false;
+                outcome.Error = new ScriptError { Kind = ScriptError.Types.Kind.Threw, Message = ex.Message };
+            }
+            result.Outcomes.Add(outcome);
+        }
+        if (ForbiddenAssemblyLoaded() is { } forbidden) DieForbidden(forbidden);
+        Send(new Envelope { LoadResult = result });
+    }
+
+    private void Admit(EvalRequest request)
+    {
+        if (_queue.Count >= _queueCapacity)
+        {
+            SendResult(new EvalResult
+            {
+                EvalId = request.EvalId,
+                Error = new ScriptError { Kind = ScriptError.Types.Kind.Busy, Message = "script worker busy" },
+            });
+            return;
+        }
+        _queue.Add(request);
+    }
+
+    private void EvalThreadLoop()
+    {
+        foreach (var request in _queue.GetConsumingEnumerable())
+        {
+            EvalResult result;
+            try
+            {
+                result = Evaluate(request);
+            }
+            catch (Exception ex)
+            {
+                result = new EvalResult
+                {
+                    EvalId = request.EvalId,
+                    Error = new ScriptError { Kind = ScriptError.Types.Kind.Threw, Message = ex.Message },
+                };
+            }
+            SendResult(result);
+        }
+    }
+
+    private EvalResult Evaluate(EvalRequest request)
+    {
+        var result = new EvalResult { EvalId = request.EvalId };
+        if (!_scripts.TryGetValue(request.Key, out var script))
+        {
+            result.Error = new ScriptError { Kind = ScriptError.Types.Kind.NotLoaded, Message = $"script '{request.Key}' is not loaded" };
+            return result;
+        }
+
+        var inputs = new Dictionary<string, DataValueSnapshot>(request.Inputs.Count, StringComparer.Ordinal);
+        foreach (var input in request.Inputs)
+        {
+            string path;
+            if (!string.IsNullOrEmpty(input.Path)) path = input.Path;
+            else if (input.Slot < script.InputPaths.Length) path = script.InputPaths[input.Slot];
+            else throw new ScriptWorkerProtocolException($"input slot {input.Slot} is not registered for '{request.Key}'");
+
+            if (input.Unsupported)
+            {
+                result.Error = new ScriptError
+                {
+                    Kind = ScriptError.Types.Kind.UnsupportedType,
+                    Message = $"input '{path}' has a value of unsupported type {input.UnsupportedType}",
+                };
+                return result;
+            }
+            inputs[path] = new DataValueSnapshot(
+                VariantCodec.Decode(input.Value),
+                input.StatusCode,
+                input.SourceTsTicks == 0 ? null : new DateTime(input.SourceTsTicks, DateTimeKind.Utc),
+                new DateTime(input.ServerTsTicks, DateTimeKind.Utc));
+        }
+
+        // ctx.Now follows the HOST clock (design §4.3) but keeps ticking: a fixed instant would never let a script
+        // that waits on ctx.Now finish.
+        var offset = request.NowUtcTicks == 0
+            ? TimeSpan.Zero
+            : new DateTime(request.NowUtcTicks, DateTimeKind.Utc) - DateTime.UtcNow;
+        Func<DateTime> clock = () => DateTime.UtcNow + offset;
+        var logger = _scriptLogger.ForContext(ForwardingLogSink.KeyProperty, request.Key);
+        var soft = TimeSpan.FromMilliseconds(Math.Max(1, request.SoftTimeoutMs));
+
+        // Cancelled by the host's Cancel frame at the soft deadline, never by our own clock (see the proto).
+        using var cts = new CancellationTokenSource();
+        var grace = request.HardGraceMs > 0 ? TimeSpan.FromMilliseconds(request.HardGraceMs) : _hardGrace;
+        var running = new RunningEval(request.Key, Stopwatch.GetTimestamp(), soft + grace + WatchdogMargin, cts);
+        _running[(long)request.EvalId] = running;
+        var before = GC.GetAllocatedBytesForCurrentThread();
+        var sw = Stopwatch.StartNew();
+        try
+        {
+            object? value = script.Run(inputs, logger, clock, cts.Token, out var isPredicate);
+            if (isPredicate)
+            {
+                result.Predicate = (bool)value!;
+            }
+            else if (VariantCodec.TryEncode(value, out var variant, out var unsupported))
+            {
+                result.Value = variant;
+            }
+            else
+            {
+                result.Error = new ScriptError
+                {
+                    Kind = ScriptError.Types.Kind.UnsupportedType,
+                    Message = $"script returned a value of unsupported type {unsupported}",
+                };
+            }
+        }
+        catch (Exception ex)
+        {
+            result.Error = new ScriptError { Kind = ScriptError.Types.Kind.Threw, Message = ex.Message };
+        }
+        finally
+        {
+            _running.TryRemove((long)request.EvalId, out _);
+        }
+        result.AllocatedBytes = (ulong)Math.Max(0, GC.GetAllocatedBytesForCurrentThread() - before);
+        result.RunMicros = (uint)Math.Min(uint.MaxValue, sw.Elapsed.TotalMicroseconds);
+        return result;
+    }
+
+    private void WatchdogLoop()
+    {
+        while (true)
+        {
+            Thread.Sleep(50);
+            foreach (var (_, run) in _running)
+            {
+                if (Stopwatch.GetElapsedTime(run.StartedTimestamp) > run.FailFastAfter)
+                {
+                    // The host should have killed us already; this names the culprit in the exit/dump.
+                    Environment.FailFast($"ScriptWorker: script '{run.Key}' exceeded its hard deadline ({run.FailFastAfter.TotalMilliseconds:F0} ms)");
+                }
+            }
+        }
+    }
+
+    private async Task HeartbeatLoopAsync()
+    {
+        using var timer = new PeriodicTimer(_heartbeatInterval);
+        while (await timer.WaitForNextTickAsync())
+        {
+            Send(new Envelope
+            {
+                Heartbeat = new Heartbeat
+                {
+                    Inflight = (uint)_running.Count,
+                    Queued = (uint)_queue.Count,
+                    HeapBytes = GC.GetTotalMemory(false),
+                    Gen2Count = (uint)GC.CollectionCount(2),
+                },
+            });
+        }
+    }
+
+    private async Task LogFlushLoopAsync()
+    {
+        using var timer = new PeriodicTimer(TimeSpan.FromMilliseconds(100));
+        while (await timer.WaitForNextTickAsync())
+        {
+            if (_logSink.Drain() is { } batch) Send(new Envelope { Logs = batch });
+        }
+    }
+
+    private async Task ParentWatchLoopAsync()
+    {
+        using var timer = new PeriodicTimer(TimeSpan.FromMilliseconds(500));
+        while (await timer.WaitForNextTickAsync())
+        {
+            if (!ParentAlive())
+            {
+                await Console.Error.WriteLineAsync("ScriptWorker: parent process is gone; exiting.");
+                Environment.Exit(ScriptWorkerEnvironment.ExitParentGone);
+            }
+        }
+    }
+
+    private bool ParentAlive()
+    {
+        try
+        {
+            using var parent = Process.GetProcessById(_parentPid);
+            return !parent.HasExited;
+        }
+        catch (ArgumentException)
+        {
+            return false;
+        }
+        catch (InvalidOperationException)
+        {
+            return false;
+        }
+    }
+
+    private async Task WriteLoopAsync()
+    {
+        var reader = _outbound.Reader;
+        var pendingResults = new EvalResults();
+        try
+        {
+            while (await reader.WaitToReadAsync())
+            {
+                // Opportunistic coalescing (design §4.5): drain whatever is queued right now, merging every completed
+                // evaluation into one EvalResults frame; no timer, so an idle pipe adds no latency.
+                while (reader.TryRead(out var envelope))
+                {
+                    if (envelope.BodyCase == Envelope.BodyOneofCase.Results)
+                    {
+                        pendingResults.Items.AddRange(envelope.Results.Items);
+                        continue;
+                    }
+                    await ScriptWorkerFrameCodec.WriteAsync(_pipe, envelope, _maxFrameBytes);
+                }
+                if (pendingResults.Items.Count > 0)
+                {
+                    await ScriptWorkerFrameCodec.WriteAsync(_pipe, Wrap(new Envelope { Results = pendingResults }), _maxFrameBytes);
+                    pendingResults = new EvalResults();
+                }
+                await _pipe.FlushAsync();
+            }
+        }
+        catch (IOException)
+        {
+            Environment.Exit(ScriptWorkerEnvironment.ExitPipeClosed);
+        }
+        catch (ObjectDisposedException)
+        {
+            Environment.Exit(ScriptWorkerEnvironment.ExitPipeClosed);
+        }
+    }
+
+    private void SendResult(EvalResult result)
+    {
+        var results = new EvalResults();
+        results.Items.Add(result);
+        Send(new Envelope { Results = results });
+    }
+
+    private void Send(Envelope envelope) => _outbound.Writer.TryWrite(Wrap(envelope));
+
+    private Envelope Wrap(Envelope envelope)
+    {
+        envelope.ProtocolVersion = ScriptWorkerFrameCodec.ProtocolVersion;
+        envelope.Seq = (ulong)Interlocked.Increment(ref _seq);
+        return envelope;
+    }
+
+    private static DiagnosticsReply Diagnostics()
+    {
+        var reply = new DiagnosticsReply
+        {
+            Pid = Environment.ProcessId,
+            WorkingDirectory = Environment.CurrentDirectory,
+        };
+        reply.LoadedAssemblies.AddRange(AppDomain.CurrentDomain.GetAssemblies()
+            .Select(a => a.GetName().Name ?? string.Empty)
+            .Where(n => n.Length > 0));
+        foreach (DictionaryEntry entry in Environment.GetEnvironmentVariables())
+            reply.EnvironmentNames.Add((string)entry.Key);
+        return reply;
+    }
+
+    private static string? ForbiddenAssemblyLoaded()
+    {
+        foreach (var assembly in AppDomain.CurrentDomain.GetAssemblies())
+        {
+            var name = assembly.GetName().Name ?? string.Empty;
+            foreach (var prefix in ScriptWorkerEnvironment.ForbiddenAssemblyPrefixes)
+                if (name.StartsWith(prefix, StringComparison.Ordinal)) return name;
+        }
+        return null;
+    }
+
+    private static void DieForbidden(string assembly)
+    {
+        Console.Error.WriteLine($"ScriptWorker: forbidden assembly '{assembly}' is loaded; exiting.");
+        Environment.Exit(ScriptWorkerEnvironment.ExitForbiddenAssembly);
+    }
+
+    private sealed record RunningEval(string Key, long StartedTimestamp, TimeSpan FailFastAfter, CancellationTokenSource Cancellation);
+
+    /// <summary>One loaded script: its compiled evaluator and its input slot order.</summary>
+    private sealed class LoadedScript : IDisposable
+    {
+        private readonly ScriptEvaluator<VirtualTagContext, object?>? _value;
+        private readonly ScriptEvaluator<AlarmPredicateContext, bool>? _predicate;
+
+        private LoadedScript(string[] inputPaths, ScriptEvaluator<VirtualTagContext, object?>? value,
+            ScriptEvaluator<AlarmPredicateContext, bool>? predicate)
+        {
+            InputPaths = inputPaths;
+            _value = value;
+            _predicate = predicate;
+        }
+
+        public string[] InputPaths { get; }
+
+        public static LoadedScript Compile(ScriptSource source) => source.Kind switch
+        {
+            ContextKind.VirtualTag or ContextKind.Calculation => new LoadedScript(
+                [.. source.InputPaths], ScriptEvaluator<VirtualTagContext, object?>.Compile(source.Source), null),
+            ContextKind.AlarmPredicate => new LoadedScript(
+                [.. source.InputPaths], null, ScriptEvaluator<AlarmPredicateContext, bool>.Compile(source.Source)),
+            _ => throw new ScriptWorkerProtocolException($"unknown script kind {source.Kind}"),
+        };
+
+        public object? Run(IReadOnlyDictionary<string, DataValueSnapshot> inputs, ILogger logger, Func<DateTime> clock,
+            CancellationToken ct, out bool isPredicate)
+        {
+            if (_predicate is not null)
+            {
+                isPredicate = true;
+                return _predicate.RunAsync(new AlarmPredicateContext(inputs, logger, clock), ct).GetAwaiter().GetResult();
+            }
+            isPredicate = false;
+            // Single-tag mode, as in the host: a cross-tag write is dropped.
+            return _value!.RunAsync(new VirtualTagContext(inputs, static (_, _) => { }, logger, clock), ct)
+                .GetAwaiter().GetResult();
+        }
+
+        public void Dispose()
+        {
+            _value?.Dispose();
+            _predicate?.Dispose();
+        }
+    }
+
+    /// <summary>Buffers <c>ctx.Logger</c> events for the host, bounded, counting what it had to drop.</summary>
+    private sealed class ForwardingLogSink : ILogEventSink
+    {
+        public const string KeyProperty = "ScriptWorkerKey";
+        private readonly ConcurrentQueue<LogLine> _lines = new();
+        private int _count;
+        private int _dropped;
+
+        public int Capacity { get; set; } = 1000;
+
+        public void Emit(LogEvent logEvent)
+        {
+            if (Interlocked.Increment(ref _count) > Capacity)
+            {
+                Interlocked.Decrement(ref _count);
+                Interlocked.Increment(ref _dropped);
+                return;
+            }
+            var key = logEvent.Properties.TryGetValue(KeyProperty, out var k) && k is ScalarValue { Value: string s } ? s : string.Empty;
+            _lines.Enqueue(new LogLine
+            {
+                Key = key,
+                Level = (uint)logEvent.Level,
+                Rendered = Truncate(logEvent.RenderMessage(), 8 * 1024),
+                Exception = Truncate(logEvent.Exception?.ToString() ?? string.Empty, 16 * 1024),
+                TsTicks = logEvent.Timestamp.UtcTicks,
+            });
+        }
+
+        public LogBatch? Drain()
+        {
+            var dropped = Interlocked.Exchange(ref _dropped, 0);
+            if (_lines.IsEmpty && dropped == 0) return null;
+            var batch = new LogBatch { Dropped = (uint)dropped };
+            while (_lines.TryDequeue(out var line))
+            {
+                Interlocked.Decrement(ref _count);
+                batch.Lines.Add(line);
+            }
+            return batch;
+        }
+
+        private static string Truncate(string value, int max) => value.Length <= max ? value : value[..max];
+    }
+}

src/Server/ZB.MOM.WW.OtOpcUa.ScriptWorker/ZB.MOM.WW.OtOpcUa.ScriptWorker.csproj

@@ -0,0 +1,32 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <!-- lmxopcua#780 — the out-of-process, pre-emptible script runner's worker (design §3, §6). A plain console app the
+         host launches per shard over a named pipe. It references only the compile/run core and the frame protocol, so
+         the host's cluster, database, OPC UA and secrets stacks are not in its assembly set; it checks itself against
+         ScriptWorkerEnvironment.ForbiddenAssemblyPrefixes at runtime as well. -->
+    <PropertyGroup>
+        <OutputType>Exe</OutputType>
+        <RootNamespace>ZB.MOM.WW.OtOpcUa.ScriptWorker</RootNamespace>
+        <AssemblyName>ZB.MOM.WW.OtOpcUa.ScriptWorker</AssemblyName>
+        <InvariantGlobalization>true</InvariantGlobalization>
+        <!-- Workstation, non-concurrent GC: the heap hard limit (DOTNET_GCHeapHardLimit) is the worker's memory bound. -->
+        <ServerGarbageCollection>false</ServerGarbageCollection>
+        <ConcurrentGarbageCollection>false</ConcurrentGarbageCollection>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <ProjectReference Include="..\..\Core\ZB.MOM.WW.OtOpcUa.Core.Scripting\ZB.MOM.WW.OtOpcUa.Core.Scripting.csproj"/>
+        <ProjectReference Include="..\..\Core\ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol\ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol.csproj"/>
+    </ItemGroup>
+
+    <!-- Core.Scripting reaches Akka and Grpc.Core.Api transitively through Commons (telemetry meter, log messages),
+         none of which the worker executes. Excluding their assets keeps them out of the worker's deps.json and output
+         folder, so they are not loadable at all, not merely unloaded (design §6 "assembly allow-list by
+         construction"). A code path that did touch them would fail with FileNotFoundException, which the
+         containment tests would catch. -->
+    <ItemGroup>
+        <PackageReference Include="Akka" ExcludeAssets="all" PrivateAssets="all"/>
+        <PackageReference Include="Grpc.Core.Api" ExcludeAssets="all" PrivateAssets="all"/>
+    </ItemGroup>
+
+</Project>

src/Server/ZB.MOM.WW.OtOpcUa.ScriptWorker/build/ScriptWorker.Deploy.targets

@@ -0,0 +1,43 @@
+<Project>
+  <!--
+    lmxopcua#780 — places the ScriptWorker next to a host that launches it: the worker's build output is copied into
+    $(OutDir)script-worker/ after Build, and into $(PublishDir)script-worker/ after Publish. Imported by the Host and by
+    the worker test project. The worker is its own app (own deps.json / runtimeconfig.json), so it lives in its own folder
+    rather than beside the host's assemblies.
+
+    Publish note: the copy is the worker's framework-dependent BUILD output, run through the dotnet muxer. That suits the
+    docker-dev image (aspnet:10.0 runtime). A self-contained host publish (the Windows deploys) needs a self-contained
+    worker publish too; that is part of the installer work tracked on lmxopcua#780.
+  -->
+  <PropertyGroup>
+    <_OtScriptWorkerProject>$(MSBuildThisFileDirectory)../ZB.MOM.WW.OtOpcUa.ScriptWorker.csproj</_OtScriptWorkerProject>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="$(_OtScriptWorkerProject)" ReferenceOutputAssembly="false" Private="false" />
+  </ItemGroup>
+
+  <Target Name="_OtResolveScriptWorkerOutput">
+    <MSBuild Projects="$(_OtScriptWorkerProject)" Targets="GetTargetPath" Properties="Configuration=$(Configuration)">
+      <Output TaskParameter="TargetOutputs" ItemName="_OtScriptWorkerTargetPath" />
+    </MSBuild>
+    <PropertyGroup>
+      <_OtScriptWorkerOutDir>@(_OtScriptWorkerTargetPath->'%(RootDir)%(Directory)')</_OtScriptWorkerOutDir>
+    </PropertyGroup>
+    <ItemGroup>
+      <_OtScriptWorkerFiles Include="$(_OtScriptWorkerOutDir)**/*" />
+    </ItemGroup>
+  </Target>
+
+  <Target Name="_OtCopyScriptWorkerAfterBuild" AfterTargets="Build" DependsOnTargets="_OtResolveScriptWorkerOutput">
+    <Copy SourceFiles="@(_OtScriptWorkerFiles)"
+          DestinationFiles="@(_OtScriptWorkerFiles->'$(OutDir)script-worker/%(RecursiveDir)%(Filename)%(Extension)')"
+          SkipUnchangedFiles="true" />
+  </Target>
+
+  <Target Name="_OtCopyScriptWorkerAfterPublish" AfterTargets="Publish" DependsOnTargets="_OtResolveScriptWorkerOutput">
+    <Copy SourceFiles="@(_OtScriptWorkerFiles)"
+          DestinationFiles="@(_OtScriptWorkerFiles->'$(PublishDir)script-worker/%(RecursiveDir)%(Filename)%(Extension)')"
+          SkipUnchangedFiles="true" />
+  </Target>
+</Project>

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation.Tests/CalculationDriverScriptRunnerTests.cs

@@ -0,0 +1,122 @@
+using System.Collections.Concurrent;
+using Serilog;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Core.Scripting;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Calculation.Tests;
+
+/// <summary>
+///     lmxopcua#780 — with <c>Scripting:Runner=OutOfProcess</c> selecting the Calculation seam, the driver hands each
+///     compiled run to the node's <see cref="IScriptRunner"/>: keyed by the calc tag's RawPath, with the driver's own
+///     budget. A runner-side failure publishes <c>BadResourceUnavailable</c> (0x80040000); a script failure keeps
+///     <c>BadInternalError</c>. The passthrough fast path never reaches the runner.
+/// </summary>
+public sealed class CalculationDriverScriptRunnerTests
+{
+    private const uint StatusGood = 0u;
+    private const uint StatusBadInternalError = 0x80020000u;
+    private const uint StatusBadResourceUnavailable = 0x80040000u;
+    private const string Tag = "calc/e/x";
+
+    private sealed class FakeRunner : IScriptRunner
+    {
+        public ConcurrentQueue<ScriptRunOutcome> Outcomes { get; } = new();
+        public ConcurrentQueue<ScriptInvocation> Invocations { get; } = new();
+        public List<ScriptContextKind> Resets { get; } = [];
+
+        public Task<ScriptRunOutcome> RunAsync(ScriptInvocation invocation, CancellationToken ct = default)
+        {
+            Invocations.Enqueue(invocation);
+            return Task.FromResult(Outcomes.TryDequeue(out var next) ? next : ScriptRunOutcome.Ok(null));
+        }
+
+        public void Reset(ScriptContextKind kind) => Resets.Add(kind);
+
+        public IReadOnlyCollection<string> QuarantinedKeys(ScriptContextKind kind) => ["q-" + kind];
+    }
+
+    private static RawTagEntry CalcTag(string source)
+    {
+        var json = $"{{\"scriptId\":\"s\",\"changeTriggered\":true,\"scriptSource\":{System.Text.Json.JsonSerializer.Serialize(source)}}}";
+        return new RawTagEntry(Tag, json, WriteIdempotent: false);
+    }
+
+    private static async Task Settle(CalculationDriver driver)
+    {
+        var deadline = DateTime.UtcNow + TimeSpan.FromSeconds(30);
+        while (DateTime.UtcNow < deadline && !driver.IsEvaluationIdle) await Task.Delay(10);
+        driver.IsEvaluationIdle.ShouldBeTrue();
+    }
+
+    private static (CalculationDriver Driver, ConcurrentQueue<DataChangeEventArgs> Published) Build(FakeRunner runner, string source)
+    {
+        var driver = new CalculationDriver(
+            new CalculationDriverOptions { RawTags = [CalcTag(source)], RunTimeout = TimeSpan.FromMilliseconds(1234), ScriptRunner = runner },
+            "calc-drv", new ScriptRootLogger(new LoggerConfiguration().CreateLogger()));
+        var published = new ConcurrentQueue<DataChangeEventArgs>();
+        driver.OnDataChange += (_, e) => published.Enqueue(e);
+        return (driver, published);
+    }
+
+    [Fact]
+    public async Task A_runner_failure_publishes_BadResourceUnavailable_and_a_script_failure_BadInternalError()
+    {
+        var runner = new FakeRunner();
+        runner.Outcomes.Enqueue(ScriptRunOutcome.Ok(30.0));
+        runner.Outcomes.Enqueue(ScriptRunOutcome.Unavailable(ScriptRunOutcome.WorkerRestartedReason));
+        runner.Outcomes.Enqueue(ScriptRunOutcome.Failed("script threw: boom"));
+        var (driver, published) = Build(runner, "return (double)ctx.GetTag(\"src/a\").Value * 3;");
+        await driver.InitializeAsync("{}", TestContext.Current.CancellationToken);
+
+        driver.OnDependencyValue("src/a", 10.0, StatusGood, DateTime.UtcNow);
+        await Settle(driver);
+        published.TryDequeue(out var good).ShouldBeTrue();
+        good!.Snapshot.StatusCode.ShouldBe(StatusGood);
+        good.Snapshot.Value.ShouldBe(30.0);
+
+        var invocation = runner.Invocations.Single();
+        invocation.Key.ShouldBe(Tag);
+        invocation.Kind.ShouldBe(ScriptContextKind.Calculation);
+        invocation.Timeout.ShouldBe(TimeSpan.FromMilliseconds(1234));
+        invocation.Inputs["src/a"].Value.ShouldBe(10.0);
+
+        driver.OnDependencyValue("src/a", 11.0, StatusGood, DateTime.UtcNow);
+        await Settle(driver);
+        published.TryDequeue(out var unavailable).ShouldBeTrue();
+        unavailable!.Snapshot.StatusCode.ShouldBe(StatusBadResourceUnavailable);
+        unavailable.Snapshot.Value.ShouldBe(30.0, "the last known value rides out with the Bad status");
+
+        driver.OnDependencyValue("src/a", 12.0, StatusGood, DateTime.UtcNow);
+        await Settle(driver);
+        published.TryDequeue(out var scriptFault).ShouldBeTrue();
+        scriptFault!.Snapshot.StatusCode.ShouldBe(StatusBadInternalError);
+    }
+
+    [Fact]
+    public async Task The_passthrough_fast_path_never_reaches_the_runner()
+    {
+        var runner = new FakeRunner();
+        var (driver, published) = Build(runner, "return ctx.GetTag(\"src/a\").Value;");
+        await driver.InitializeAsync("{}", TestContext.Current.CancellationToken);
+
+        driver.OnDependencyValue("src/a", 4.0, StatusGood, DateTime.UtcNow);
+        await Settle(driver);
+        published.TryDequeue(out var mirrored).ShouldBeTrue();
+        mirrored!.Snapshot.Value.ShouldBe(4.0);
+        runner.Invocations.ShouldBeEmpty();
+    }
+
+    [Fact]
+    public void The_deploy_boundary_resets_the_runners_calculation_seam_and_quarantines_are_reported()
+    {
+        var runner = new FakeRunner();
+        using var evaluator = new CalculationEvaluator(Microsoft.Extensions.Logging.Abstractions.NullLogger.Instance,
+            new ScriptRootLogger(new LoggerConfiguration().CreateLogger()), scriptRunner: runner);
+        evaluator.ClearCompiledScripts();
+        evaluator.ResetQuarantines();
+        runner.Resets.ShouldBe([ScriptContextKind.Calculation, ScriptContextKind.Calculation]);
+        evaluator.QuarantinedScripts.ShouldBe(["q-Calculation"]);
+    }
+}

tests/Server/ZB.MOM.WW.OtOpcUa.Host.Tests/Configuration/ScriptRunnerSelectionTests.cs

@@ -0,0 +1,170 @@
+using Microsoft.Extensions.Configuration;
+using Serilog;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Scripting;
+using ZB.MOM.WW.OtOpcUa.Host.Configuration;
+
+namespace ZB.MOM.WW.OtOpcUa.Host.Tests.Configuration;
+
+/// <summary>
+///     lmxopcua#780 — <c>Scripting:Runner</c> binds by its documented keys (design §12), defaults to InProcess (every seam
+///     gets no runner, so the in-process path is untouched), and the worker options clamp and fail closed.
+/// </summary>
+public sealed class ScriptRunnerSelectionTests
+{
+    private static IConfiguration Config(Dictionary<string, string?> values) =>
+        new ConfigurationBuilder().AddInMemoryCollection(values).Build();
+
+    private static readonly ILogger Silent = new LoggerConfiguration().CreateLogger();
+
+    [Fact]
+    public void The_default_is_InProcess_and_selects_no_runner_for_any_seam()
+    {
+        var bound = ScriptingOptionsBinding.Bind(Config(new()), out var adjustments);
+        adjustments.ShouldBeEmpty();
+        bound.Runner.ShouldBe(ScriptRunnerMode.InProcess);
+        ScriptRunnerSelection.Validate(bound, "/srv/app").ShouldBeEmpty();
+        using var selection = ScriptRunnerSelection.Create(bound, Silent, null);
+        foreach (var seam in Enum.GetValues<ScriptSeam>()) selection.ForSeam(seam).ShouldBeNull(seam.ToString());
+        selection.OutOfProcessRunner.ShouldBeNull();
+    }
+
+    [Fact]
+    public void Every_documented_runner_key_binds()
+    {
+        var bound = ScriptingOptionsBinding.Bind(Config(new()
+        {
+            ["Scripting:Runner"] = "OutOfProcess",
+            ["Scripting:Runner:Seams:0"] = "Calculation",
+            ["Scripting:Worker:Shards"] = "3",
+            ["Scripting:Worker:HardGrace"] = "00:00:02",
+            ["Scripting:Worker:HeapLimitBytes"] = "268435456",
+            ["Scripting:Worker:QuarantineAfterKills"] = "4",
+            ["Scripting:Worker:UnavailableGrace"] = "00:00:07",
+            ["Scripting:Worker:IsolationProbationRuns"] = "9",
+            ["Scripting:Worker:PeCacheDir"] = "/var/cache/otopcua-pe",
+            ["Scripting:Worker:ExecutablePath"] = "/opt/w/ZB.MOM.WW.OtOpcUa.ScriptWorker.dll",
+        }), out var adjustments);
+
+        adjustments.ShouldBeEmpty();
+        bound.Runner.ShouldBe(ScriptRunnerMode.OutOfProcess);
+        bound.RunnerSeams.ShouldBe([ScriptSeam.Calculation]);
+        bound.Worker.Shards.ShouldBe(3);
+        bound.Worker.HardGrace.ShouldBe(TimeSpan.FromSeconds(2));
+        bound.Worker.HeapLimitBytes.ShouldBe(256L * 1024 * 1024);
+        bound.Worker.QuarantineAfterKills.ShouldBe(4);
+        bound.Worker.UnavailableGrace.ShouldBe(TimeSpan.FromSeconds(7));
+        bound.Worker.IsolationProbationRuns.ShouldBe(9);
+        bound.Worker.PeCacheDir.ShouldBe("/var/cache/otopcua-pe");
+        bound.Worker.ExecutablePath.ShouldBe("/opt/w/ZB.MOM.WW.OtOpcUa.ScriptWorker.dll");
+        bound.IsOutOfProcess(ScriptSeam.Calculation).ShouldBeTrue();
+        bound.IsOutOfProcess(ScriptSeam.VirtualTag).ShouldBeFalse();
+    }
+
+    [Fact]
+    public void A_misspelled_runner_mode_fails_startup()
+        => Should.Throw<InvalidOperationException>(() =>
+            ScriptingOptionsBinding.Bind(Config(new() { ["Scripting:Runner"] = "OutOfProc" }), out _));
+
+    [Fact]
+    public void Worker_values_out_of_range_are_clamped_and_reported()
+    {
+        var bound = ScriptingOptionsBinding.Bind(Config(new()
+        {
+            ["Scripting:Worker:Shards"] = "64",
+            ["Scripting:Worker:HardGrace"] = "00:00:00.010",
+            ["Scripting:Worker:HeapLimitBytes"] = "1024",
+            ["Scripting:Worker:QuarantineAfterKills"] = "0",
+            ["Scripting:Worker:UnavailableGrace"] = "00:05:00",
+            ["Scripting:Worker:IsolationProbationRuns"] = "0",
+        }), out var adjustments);
+
+        bound.Worker.Shards.ShouldBe(ScriptWorkerOptions.MaxShards);
+        bound.Worker.HardGrace.ShouldBe(ScriptWorkerOptions.MinHardGrace);
+        bound.Worker.HeapLimitBytes.ShouldBe(ScriptWorkerOptions.MinHeapLimitBytes);
+        bound.Worker.QuarantineAfterKills.ShouldBe(1);
+        bound.Worker.UnavailableGrace.ShouldBe(ScriptWorkerOptions.MaxUnavailableGrace);
+        bound.Worker.IsolationProbationRuns.ShouldBe(1);
+        adjustments.Count.ShouldBe(6);
+        adjustments.ShouldAllBe(a => a.StartsWith("Scripting:Worker:"));
+    }
+
+    [Fact]
+    public void The_hard_grace_defaults_to_max_of_one_second_and_the_budget()
+    {
+        var worker = new ScriptWorkerOptions();
+        worker.EffectiveHardGrace(TimeSpan.FromMilliseconds(250)).ShouldBe(TimeSpan.FromSeconds(1));
+        worker.EffectiveHardGrace(TimeSpan.FromSeconds(2)).ShouldBe(TimeSpan.FromSeconds(2));
+        new ScriptWorkerOptions { HardGrace = TimeSpan.FromMilliseconds(400) }
+            .EffectiveHardGrace(TimeSpan.FromSeconds(2)).ShouldBe(TimeSpan.FromMilliseconds(400));
+    }
+
+    [Theory]
+    [InlineData("relative/cache", "must be an absolute path")]
+    [InlineData("{root}/pe-cache", "inside the content root")]
+    [InlineData("{root}", "inside the content root")]
+    public void A_pe_cache_dir_that_is_relative_or_inside_the_content_root_fails_startup(string dir, string why)
+    {
+        var root = Path.Combine(Path.GetTempPath(), "otopcua-root-" + Guid.NewGuid().ToString("N"));
+        var options = new ScriptingOptions
+        {
+            Runner = ScriptRunnerMode.OutOfProcess,
+            Worker = new ScriptWorkerOptions { PeCacheDir = dir.Replace("{root}", root) },
+        };
+        Should.Throw<InvalidOperationException>(() => ScriptRunnerSelection.Validate(options, root)).Message.ShouldContain(why);
+    }
+
+    [Fact]
+    public void A_pe_cache_dir_outside_the_content_root_is_accepted()
+    {
+        var root = Path.Combine(Path.GetTempPath(), "otopcua-root");
+        var options = new ScriptingOptions
+        {
+            Runner = ScriptRunnerMode.OutOfProcess,
+            Worker = new ScriptWorkerOptions { PeCacheDir = Path.Combine(Path.GetTempPath(), "otopcua-root-sibling") },
+        };
+        Should.NotThrow(() => ScriptRunnerSelection.Validate(options, root));
+    }
+
+    [Fact]
+    public void Shadow_is_not_implemented_yet_and_runs_in_process_with_a_warning()
+    {
+        var options = new ScriptingOptions { Runner = ScriptRunnerMode.Shadow };
+        ScriptRunnerSelection.Validate(options, "/srv").ShouldHaveSingleItem().ShouldContain("Shadow");
+        using var selection = ScriptRunnerSelection.Create(options, Silent, null);
+        selection.OutOfProcessRunner.ShouldBeNull();
+    }
+
+    [Fact]
+    public void OutOfProcess_selects_only_the_supported_requested_seams()
+    {
+        var all = new ScriptingOptions { Runner = ScriptRunnerMode.OutOfProcess };
+        ScriptRunnerSelection.Validate(all, "/srv").ShouldContain(w => w.Contains("ScriptedAlarm seam cannot run out of process yet"));
+        using (var selection = ScriptRunnerSelection.Create(all, Silent, null))
+        {
+            selection.ForSeam(ScriptSeam.VirtualTag).ShouldNotBeNull();
+            selection.ForSeam(ScriptSeam.Calculation).ShouldBeSameAs(selection.ForSeam(ScriptSeam.VirtualTag), "one node-wide runner");
+            selection.ForSeam(ScriptSeam.ScriptedAlarm).ShouldBeNull();
+        }
+
+        var calcOnly = new ScriptingOptions { Runner = ScriptRunnerMode.OutOfProcess, RunnerSeams = [ScriptSeam.Calculation] };
+        using (var selection = ScriptRunnerSelection.Create(calcOnly, Silent, null))
+        {
+            selection.ForSeam(ScriptSeam.Calculation).ShouldNotBeNull();
+            selection.ForSeam(ScriptSeam.VirtualTag).ShouldBeNull();
+        }
+    }
+
+    [Fact]
+    public void A_missing_worker_is_a_startup_warning_not_a_silent_in_process_fallback()
+    {
+        var options = new ScriptingOptions
+        {
+            Runner = ScriptRunnerMode.OutOfProcess,
+            RunnerSeams = [ScriptSeam.VirtualTag],
+            Worker = new ScriptWorkerOptions { ExecutablePath = Path.Combine(Path.GetTempPath(), "missing-" + Guid.NewGuid().ToString("N"), "w.dll") },
+        };
+        ScriptRunnerSelection.Validate(options, "/srv").ShouldHaveSingleItem().ShouldContain("BadResourceUnavailable");
+    }
+}

tests/Server/ZB.MOM.WW.OtOpcUa.Host.Tests/Engines/RoslynVirtualTagEvaluatorScriptRunnerTests.cs

@@ -0,0 +1,109 @@
+using System.Collections.Concurrent;
+using Microsoft.Extensions.Logging.Abstractions;
+using Serilog;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Commons.OpcUa;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Core.Scripting;
+using ZB.MOM.WW.OtOpcUa.Host.Engines;
+
+namespace ZB.MOM.WW.OtOpcUa.Host.Tests.Engines;
+
+/// <summary>
+///     lmxopcua#780 — the virtual-tag seam over <see cref="IScriptRunner"/>: with a runner (OutOfProcess) the compiled run
+///     is the runner's, keyed by virtual-tag id with the evaluator's budget, and its Unavailable outcome becomes a failure
+///     carrying <see cref="OpcUaStatus.BadResourceUnavailable"/>. Without one (the InProcess default) nothing changes.
+/// </summary>
+public sealed class RoslynVirtualTagEvaluatorScriptRunnerTests
+{
+    private sealed class FakeRunner : IScriptRunner
+    {
+        public ConcurrentQueue<ScriptRunOutcome> Outcomes { get; } = new();
+        public ConcurrentQueue<ScriptInvocation> Invocations { get; } = new();
+        public List<ScriptContextKind> Resets { get; } = [];
+
+        public Task<ScriptRunOutcome> RunAsync(ScriptInvocation invocation, CancellationToken ct = default)
+        {
+            Invocations.Enqueue(invocation);
+            return Task.FromResult(Outcomes.TryDequeue(out var next) ? next : ScriptRunOutcome.Ok(null));
+        }
+
+        public void Reset(ScriptContextKind kind) => Resets.Add(kind);
+
+        public IReadOnlyCollection<string> QuarantinedKeys(ScriptContextKind kind) => ["vt-q"];
+    }
+
+    private static RoslynVirtualTagEvaluator Build(IScriptRunner? runner) =>
+        new(NullLogger<RoslynVirtualTagEvaluator>.Instance, new ScriptRootLogger(new LoggerConfiguration().CreateLogger()),
+            runTimeout: TimeSpan.FromMilliseconds(1500), scriptRunner: runner);
+
+    private static Dictionary<string, DataValueSnapshot> Deps(int a) => new(StringComparer.Ordinal)
+    {
+        ["a"] = new DataValueSnapshot(a, 0u, DateTime.UtcNow, DateTime.UtcNow),
+    };
+
+    [Fact]
+    public async Task Compiled_runs_go_to_the_runner_and_its_outcomes_map_onto_the_seam_contract()
+    {
+        var runner = new FakeRunner();
+        runner.Outcomes.Enqueue(ScriptRunOutcome.Ok(42));
+        runner.Outcomes.Enqueue(ScriptRunOutcome.Unavailable(ScriptRunOutcome.WorkerRestartedReason));
+        runner.Outcomes.Enqueue(ScriptRunOutcome.Failed("script threw: boom"));
+        using var sut = Build(runner);
+        const string script = "return (int)ctx.GetTag(\"a\").Value + 1;";
+
+        var ok = await sut.EvaluateAsync("vt-1", script, Deps(41));
+        ok.Success.ShouldBeTrue();
+        ok.Value.ShouldBe(42);
+        ok.StatusCode.ShouldBeNull();
+
+        var unavailable = await sut.EvaluateAsync("vt-1", script, Deps(41));
+        unavailable.Success.ShouldBeFalse();
+        unavailable.Reason.ShouldBe(ScriptRunOutcome.WorkerRestartedReason);
+        unavailable.StatusCode.ShouldBe(OpcUaStatus.BadResourceUnavailable);
+
+        var failed = await sut.EvaluateAsync("vt-1", script, Deps(41));
+        failed.Reason.ShouldBe("script threw: boom");
+        failed.StatusCode.ShouldBeNull("a script failure keeps BadInternalError");
+
+        var invocation = runner.Invocations.First();
+        invocation.Key.ShouldBe("vt-1");
+        invocation.Kind.ShouldBe(ScriptContextKind.VirtualTag);
+        invocation.Source.ShouldBe(script);
+        invocation.Timeout.ShouldBe(TimeSpan.FromMilliseconds(1500));
+        invocation.Inputs["a"].Value.ShouldBe(41);
+        invocation.ScriptLogger.ShouldNotBeNull();
+    }
+
+    [Fact]
+    public async Task The_passthrough_fast_path_and_an_empty_expression_never_reach_the_runner()
+    {
+        var runner = new FakeRunner();
+        using var sut = Build(runner);
+        (await sut.EvaluateAsync("vt-p", "return ctx.GetTag(\"a\").Value;", Deps(7))).Value.ShouldBe(7);
+        (await sut.EvaluateAsync("vt-e", " ", Deps(7))).Success.ShouldBeFalse();
+        runner.Invocations.ShouldBeEmpty();
+    }
+
+    [Fact]
+    public void The_deploy_boundary_resets_the_runners_virtual_tag_seam_and_its_quarantines_are_reported()
+    {
+        var runner = new FakeRunner();
+        using var sut = Build(runner);
+        sut.ClearCompiledScripts();
+        sut.ResetQuarantines();
+        runner.Resets.ShouldBe([ScriptContextKind.VirtualTag, ScriptContextKind.VirtualTag]);
+        sut.QuarantinedScripts.ShouldBe(["vt-q"]);
+    }
+
+    /// <summary>Positive control for the default: no runner means the in-process Roslyn path actually runs the script.</summary>
+    [Fact]
+    public async Task Without_a_runner_the_script_runs_in_process()
+    {
+        using var sut = Build(runner: null);
+        sut.ScriptRunner.ShouldBeNull();
+        (await sut.EvaluateAsync("vt-1", "return (int)ctx.GetTag(\"a\").Value + 1;", Deps(41))).Value.ShouldBe(42);
+        sut.RunGuard.StartedRunCount.ShouldBe(1);
+    }
+}

tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/VirtualTags/VirtualTagActorRunnerUnavailableTests.cs

@@ -0,0 +1,64 @@
+using System.Collections.Concurrent;
+using Akka.Actor;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Commons.Engines;
+using ZB.MOM.WW.OtOpcUa.Commons.OpcUa;
+using ZB.MOM.WW.OtOpcUa.Runtime.Tests.Harness;
+using ZB.MOM.WW.OtOpcUa.Runtime.VirtualTags;
+
+namespace ZB.MOM.WW.OtOpcUa.Runtime.Tests.VirtualTags;
+
+/// <summary>
+///     lmxopcua#780 — when the out-of-process runner, not the script, fails (its worker restarted, no worker ready), the
+///     virtual tag publishes <see cref="OpcUaStatus.BadResourceUnavailable"/> with its last value, so a client can tell a
+///     sick node from a broken script. Every other failure keeps the long-standing <see cref="OpcUaStatus.BadInternalError"/>.
+/// </summary>
+public sealed class VirtualTagActorRunnerUnavailableTests : RuntimeActorTestBase
+{
+    private sealed class QueuedEvaluator : IVirtualTagEvaluator
+    {
+        public ConcurrentQueue<VirtualTagEvalResult> Results { get; } = new();
+
+        public VirtualTagEvalResult Evaluate(string virtualTagId, string expression, IReadOnlyDictionary<string, object?> dependencies)
+            => Results.TryDequeue(out var next) ? next : VirtualTagEvalResult.NoChange;
+    }
+
+    [Fact]
+    public void A_runner_unavailable_failure_publishes_BadResourceUnavailable_and_a_script_failure_BadInternalError()
+    {
+        var parent = CreateTestProbe();
+        var evaluator = new QueuedEvaluator();
+        evaluator.Results.Enqueue(VirtualTagEvalResult.Ok(5));
+        evaluator.Results.Enqueue(VirtualTagEvalResult.Unavailable("script worker restarted"));
+        evaluator.Results.Enqueue(VirtualTagEvalResult.Unavailable("script worker restarted"));
+        evaluator.Results.Enqueue(VirtualTagEvalResult.Failure("script threw: boom"));
+        var actor = parent.ChildActorOf(VirtualTagActor.Props("vt-1", "x", evaluator: evaluator, dependencyRefs: ["a"]));
+
+        actor.Tell(new VirtualTagActor.DependencyValueChanged("a", 1, DateTime.UtcNow));
+        parent.ExpectMsg<VirtualTagActor.EvaluationResult>().StatusCode.ShouldBe(OpcUaStatus.Good);
+
+        actor.Tell(new VirtualTagActor.DependencyValueChanged("a", 2, DateTime.UtcNow));
+        var unavailable = parent.ExpectMsg<VirtualTagActor.EvaluationResult>(PresenceBudget);
+        unavailable.StatusCode.ShouldBe(OpcUaStatus.BadResourceUnavailable);
+        unavailable.Value.ShouldBe(5, "the last known value rides out with the Bad status");
+
+        // Once per transition: the same code again publishes nothing.
+        actor.Tell(new VirtualTagActor.DependencyValueChanged("a", 3, DateTime.UtcNow));
+        parent.ExpectNoMsg(TimeSpan.FromMilliseconds(300));
+
+        // A script failure is a different Bad and is published.
+        actor.Tell(new VirtualTagActor.DependencyValueChanged("a", 4, DateTime.UtcNow));
+        var scriptFault = parent.ExpectMsg<VirtualTagActor.EvaluationResult>(PresenceBudget);
+        scriptFault.StatusCode.ShouldBe(OpcUaStatus.BadInternalError);
+        scriptFault.Value.ShouldBe(5);
+    }
+
+    [Fact]
+    public void A_failure_without_a_status_keeps_BadInternalError()
+    {
+        VirtualTagEvalResult.Failure("x").StatusCode.ShouldBeNull();
+        VirtualTagEvalResult.Unavailable("x").StatusCode.ShouldBe(OpcUaStatus.BadResourceUnavailable);
+        OpcUaStatus.BadResourceUnavailable.ShouldBe(0x80040000u, "the OPC UA Part 6 code ScadaBridge maps");
+    }
+}

tests/Server/ZB.MOM.WW.OtOpcUa.ScriptWorker.Tests/ContainmentTests.cs

@@ -0,0 +1,382 @@
+using System.Diagnostics;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Core.Scripting;
+using ZB.MOM.WW.OtOpcUa.Core.Scripting.OutOfProcess;
+using ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol;
+
+namespace ZB.MOM.WW.OtOpcUa.ScriptWorker.Tests;
+
+/// <summary>Worker-backed tests spawn real processes and measure wall-clock bounds, so they never run in parallel.</summary>
+[CollectionDefinition(Name, DisableParallelization = true)]
+public sealed class ScriptWorkerCollection
+{
+    public const string Name = "ScriptWorker";
+}
+
+/// <summary>
+///     lmxopcua#780 design §13 "Containment": each case runs against the real <c>ScriptWorker</c> process, and each has a
+///     positive control — a healthy sibling on the SAME shard (every runner here has one shard) that keeps producing
+///     correct values before and after the event.
+/// </summary>
+[Collection(ScriptWorkerCollection.Name)]
+[Trait("Category", "ScriptWorker")]
+public sealed class ContainmentTests
+{
+    private const string Healthy = "return 7;";
+    private const string Runaway = "while (true) { }";
+    private const string Cooperative = "while (!ctx.CancellationToken.IsCancellationRequested) { } return 1;";
+
+    /// <summary>Spins for the number of milliseconds in input <c>ms</c>, so one source serves slow and fast runs.</summary>
+    private const string Spin = "var ms = (int)ctx.GetTag(\"ms\").Value; var end = ctx.Now.AddMilliseconds(ms); while (ctx.Now < end) { } return ms;";
+
+    private static IReadOnlyDictionary<string, DataValueSnapshot> Ms(int ms) => Scripts.Input("ms", ms);
+
+    private static CancellationToken Ct => TestContext.Current.CancellationToken;
+
+    [Fact]
+    public async Task A_healthy_script_runs_out_of_process_and_reads_its_inputs()
+    {
+        await using var runner = Scripts.Runner(Scripts.Options());
+        var outcome = await runner.RunAsync(Scripts.Vt("vt", "return (int)ctx.GetTag(\"x\").Value + 1;",
+            inputs: Scripts.Input("x", 41)), Ct);
+
+        outcome.Status.ShouldBe(ScriptRunStatus.Ok, outcome.Reason);
+        outcome.Value.ShouldBe(42);
+        runner.Shards[0].Current.ShouldNotBeNull().Pid.ShouldNotBe(Environment.ProcessId);
+    }
+
+    /// <summary>
+    ///     The headline case: <c>while(true){}</c> ignores the token. In process it would spin a host core forever; here
+    ///     the caller gets the usual timeout at T, the worker is killed at T + G, the host burns no CPU on it, and the
+    ///     sibling on the same shard keeps working. Mutation check: with the hard-deadline kill disabled the worker is
+    ///     never killed and the Exited wait times out.
+    /// </summary>
+    [Fact]
+    public async Task A_runaway_script_is_killed_at_its_hard_deadline_and_its_sibling_keeps_working()
+    {
+        var softT = TimeSpan.FromMilliseconds(400);
+        var grace = TimeSpan.FromMilliseconds(500);
+        await using var runner = Scripts.Runner(Scripts.Options(hardGrace: grace, quarantineAfterKills: 2));
+
+        (await runner.RunAsync(Scripts.Vt("sibling", Healthy), Ct)).Value.ShouldBe(7);
+        var worker = runner.Shards[0].Current.ShouldNotBeNull();
+
+        var sw = Stopwatch.StartNew();
+        var outcome = await runner.RunAsync(Scripts.Vt("runaway", Runaway, softT), Ct);
+        var softElapsed = sw.Elapsed;
+        outcome.Status.ShouldBe(ScriptRunStatus.Failed);
+        outcome.Reason!.ShouldStartWith("script timed out after ");
+        softElapsed.ShouldBeLessThan(softT + TimeSpan.FromMilliseconds(400), "the caller is answered at the soft deadline");
+
+        var exit = await worker.Exited.WaitAsync(TimeSpan.FromSeconds(10), Ct);
+        var killElapsed = sw.Elapsed;
+        exit.Reason.ShouldBe(WorkerExitReason.KilledDeadline);
+        exit.CulpritKey.ShouldBe(InProcessScriptRunner.ScopedKey(ScriptContextKind.VirtualTag, "runaway"));
+        killElapsed.ShouldBeGreaterThanOrEqualTo(softT + grace - TimeSpan.FromMilliseconds(50));
+        // Design budget is T + G + 100 ms; the slack here is for a loaded CI box (process reap + exit notification).
+        killElapsed.ShouldBeLessThan(softT + grace + TimeSpan.FromMilliseconds(1500));
+
+        // No orphan in the host: an in-process while(true) would burn one host core for the whole window.
+        var cpuBefore = Process.GetCurrentProcess().TotalProcessorTime;
+        await Task.Delay(TimeSpan.FromMilliseconds(1500), Ct);
+        var cpuUsed = Process.GetCurrentProcess().TotalProcessorTime - cpuBefore;
+        cpuUsed.ShouldBeLessThan(TimeSpan.FromMilliseconds(1000), "the runaway's thread died with its worker");
+
+        // The sibling recovers on a fresh worker.
+        (await runner.RunAsync(Scripts.Vt("sibling", Healthy), Ct)).Value.ShouldBe(7);
+        runner.Shards[0].Current.ShouldNotBeNull().Pid.ShouldNotBe(worker.Pid);
+
+        // A second kill quarantines (QuarantineAfterKills = 2); the third trigger is refused without running.
+        var second = runner.Shards[0].Current!;
+        (await runner.RunAsync(Scripts.Vt("runaway", Runaway, softT), Ct)).Status.ShouldBe(ScriptRunStatus.Failed);
+        (await second.Exited.WaitAsync(TimeSpan.FromSeconds(10), Ct)).Reason.ShouldBe(WorkerExitReason.KilledDeadline);
+        // The strike is recorded by the shard's exit handler, which runs asynchronously to the Exited completion.
+        await Scripts.Eventually(() => runner.QuarantinedKeys(ScriptContextKind.VirtualTag).Count == 1,
+            TimeSpan.FromSeconds(5), "the second kill strike");
+        var refused = await runner.RunAsync(Scripts.Vt("runaway", Runaway, softT), Ct);
+        refused.Reason!.ShouldStartWith(ScriptRunGuard.QuarantinedReasonPrefix);
+        refused.Reason.ShouldContain("hard deadline");
+        runner.QuarantinedKeys(ScriptContextKind.VirtualTag).ShouldBe(["runaway"]);
+        (await runner.RunAsync(Scripts.Vt("sibling", Healthy), Ct)).Value.ShouldBe(7);
+
+        // Lifted by a source change (the operator fixed it)…
+        (await runner.RunAsync(Scripts.Vt("runaway", "return 1;"), Ct)).Value.ShouldBe(1);
+        runner.QuarantinedKeys(ScriptContextKind.VirtualTag).ShouldBeEmpty();
+    }
+
+    [Fact]
+    public async Task A_redeploy_lifts_a_kill_quarantine_for_its_seam_only()
+    {
+        var softT = TimeSpan.FromMilliseconds(300);
+        await using var runner = Scripts.Runner(Scripts.Options(hardGrace: TimeSpan.FromMilliseconds(300), quarantineAfterKills: 1));
+
+        (await runner.RunAsync(Scripts.Vt("runaway", Runaway, softT), Ct)).Status.ShouldBe(ScriptRunStatus.Failed);
+        await Scripts.Eventually(() => runner.QuarantinedKeys(ScriptContextKind.VirtualTag).Count == 1, TimeSpan.FromSeconds(10), "the kill quarantine");
+
+        runner.Reset(ScriptContextKind.Calculation);
+        runner.QuarantinedKeys(ScriptContextKind.VirtualTag).ShouldBe(["runaway"], "another seam's redeploy leaves it alone");
+        runner.Reset(ScriptContextKind.VirtualTag);
+        runner.QuarantinedKeys(ScriptContextKind.VirtualTag).ShouldBeEmpty();
+    }
+
+    /// <summary>A script that polls its token ends itself at T: no kill, no strike beyond the timeout (design §13).</summary>
+    [Fact]
+    public async Task A_cooperative_script_ends_at_its_soft_deadline_without_a_kill()
+    {
+        var softT = TimeSpan.FromMilliseconds(400);
+        var grace = TimeSpan.FromMilliseconds(1500);
+        await using var runner = Scripts.Runner(Scripts.Options(hardGrace: grace, quarantineAfterKills: 1));
+        (await runner.RunAsync(Scripts.Vt("sibling", Healthy), Ct)).Value.ShouldBe(7);
+        var worker = runner.Shards[0].Current.ShouldNotBeNull();
+
+        var outcome = await runner.RunAsync(Scripts.Vt("polite", Cooperative, softT), Ct);
+        outcome.Reason!.ShouldStartWith("script timed out after ");
+
+        await Task.Delay(softT + grace + TimeSpan.FromMilliseconds(500), Ct);
+        worker.IsAlive.ShouldBeTrue("a script that ended itself must not cost the shard a restart");
+        runner.Shards[0].Current!.Pid.ShouldBe(worker.Pid);
+        runner.QuarantinedKeys(ScriptContextKind.VirtualTag).ShouldBeEmpty("no kill strike (QuarantineAfterKills = 1)");
+        (await runner.RunAsync(Scripts.Vt("sibling", Healthy), Ct)).Value.ShouldBe(7);
+    }
+
+    [Fact]
+    public async Task A_second_trigger_while_the_first_still_runs_is_refused_not_queued()
+    {
+        await using var runner = Scripts.Runner(Scripts.Options());
+        (await runner.RunAsync(Scripts.Vt("spin", Spin, inputs: Ms(0)), Ct)).Value.ShouldBe(0);
+
+        var first = runner.RunAsync(Scripts.Vt("spin", Spin, inputs: Ms(1500)), Ct);
+        await Task.Delay(200, Ct);
+        var second = await runner.RunAsync(Scripts.Vt("spin", Spin, inputs: Ms(0)), Ct);
+        second.Reason.ShouldBe(ScriptRunGuard.PreviousRunStillRunningReason);
+        (await first).Value.ShouldBe(1500);
+    }
+
+    /// <summary>
+    ///     <c>kill -9</c> of the worker: the evaluation in flight is a victim — Unavailable "script worker restarted"
+    ///     (BadResourceUnavailable), not a script fault — and, with no deadline crossed, a suspect that proves itself in
+    ///     the isolation worker and then returns to its shard.
+    /// </summary>
+    [Fact]
+    public async Task An_externally_killed_worker_makes_its_in_flight_script_a_suspect_that_recovers_in_isolation()
+    {
+        await using var runner = Scripts.Runner(Scripts.Options(probation: 2));
+        (await runner.RunAsync(Scripts.Vt("spin", Spin, inputs: Ms(0)), Ct)).Value.ShouldBe(0);
+        var worker = runner.Shards[0].Current.ShouldNotBeNull();
+
+        var inFlight = runner.RunAsync(Scripts.Vt("spin", Spin, TimeSpan.FromSeconds(20), Ms(5000)), Ct);
+        await Task.Delay(300, Ct);
+        Process.GetProcessById(worker.Pid).Kill();
+
+        var victim = await inFlight.WaitAsync(TimeSpan.FromSeconds(10), Ct);
+        victim.Status.ShouldBe(ScriptRunStatus.Unavailable);
+        victim.Reason.ShouldBe(ScriptRunOutcome.WorkerRestartedReason);
+        (await worker.Exited).Reason.ShouldBe(WorkerExitReason.Crash);
+        runner.SuspectKeys.ShouldBe([InProcessScriptRunner.ScopedKey(ScriptContextKind.VirtualTag, "spin")]);
+
+        (await runner.RunAsync(Scripts.Vt("spin", Spin, inputs: Ms(0)), Ct)).Value.ShouldBe(0);
+        runner.Isolation.Current.ShouldNotBeNull("a suspect runs in the isolation worker");
+        (await runner.RunAsync(Scripts.Vt("spin", Spin, inputs: Ms(0)), Ct)).Value.ShouldBe(0);
+        runner.SuspectKeys.ShouldBeEmpty("two clean runs (probation = 2) return it to its shard");
+        runner.QuarantinedKeys(ScriptContextKind.VirtualTag).ShouldBeEmpty();
+
+        // The sibling recovers on a fresh shard worker.
+        (await runner.RunAsync(Scripts.Vt("sibling", Healthy), Ct)).Value.ShouldBe(7);
+        runner.Shards[0].Current!.Pid.ShouldNotBe(worker.Pid);
+    }
+
+    /// <summary>The isolation worker runs one evaluation at a time, so a crash there names exactly one key.</summary>
+    [Fact]
+    public async Task A_crash_in_the_isolation_worker_strikes_its_one_key_and_quarantines_it()
+    {
+        await using var runner = Scripts.Runner(Scripts.Options(quarantineAfterKills: 2));
+        (await runner.RunAsync(Scripts.Vt("spin", Spin, inputs: Ms(0)), Ct)).Value.ShouldBe(0);
+
+        async Task<ScriptRunOutcome> RunAndKill(Func<WorkerConnection?> worker)
+        {
+            var run = runner.RunAsync(Scripts.Vt("spin", Spin, TimeSpan.FromSeconds(20), Ms(5000)), Ct);
+            var live = await Scripts.Eventually(worker, TimeSpan.FromSeconds(15), "a live worker");
+            await Scripts.Eventually(() => live.InFlightCount == 1, TimeSpan.FromSeconds(15), "the evaluation in flight");
+            await Task.Delay(200, Ct);
+            Process.GetProcessById(live.Pid).Kill();
+            return await run.WaitAsync(TimeSpan.FromSeconds(10), Ct);
+        }
+
+        (await RunAndKill(() => runner.Shards[0].Current)).Reason.ShouldBe(ScriptRunOutcome.WorkerRestartedReason);
+        runner.SuspectKeys.Count.ShouldBe(1);
+        runner.QuarantinedKeys(ScriptContextKind.VirtualTag).ShouldBeEmpty("an ambiguous shard crash is not a strike");
+
+        (await RunAndKill(() => runner.Isolation.Current)).Reason.ShouldBe(ScriptRunOutcome.WorkerRestartedReason);
+        runner.QuarantinedKeys(ScriptContextKind.VirtualTag).ShouldBeEmpty("one isolation crash is one strike");
+        (await RunAndKill(() => runner.Isolation.Current)).Reason.ShouldBe(ScriptRunOutcome.WorkerRestartedReason);
+        await Scripts.Eventually(() => runner.QuarantinedKeys(ScriptContextKind.VirtualTag).Count == 1,
+            TimeSpan.FromSeconds(5), "the isolated-crash quarantine");
+
+        var refused = await runner.RunAsync(Scripts.Vt("spin", Spin, inputs: Ms(0)), Ct);
+        refused.Reason!.ShouldStartWith(ScriptRunGuard.QuarantinedReasonPrefix);
+        refused.Reason.ShouldContain("isolation worker");
+        (await runner.RunAsync(Scripts.Vt("sibling", Healthy), Ct)).Value.ShouldBe(7);
+    }
+
+    /// <summary>A deadline kill blames exactly one key: the sibling in flight on the same worker is a victim, not a suspect.</summary>
+    [Fact]
+    public async Task A_deadline_kill_blames_only_its_culprit()
+    {
+        await using var runner = Scripts.Runner(Scripts.Options(hardGrace: TimeSpan.FromMilliseconds(300), quarantineAfterKills: 1));
+        (await runner.RunAsync(Scripts.Vt("spin", Spin, inputs: Ms(0)), Ct)).Value.ShouldBe(0);
+        (await runner.RunAsync(Scripts.Vt("warm", Healthy), Ct)).Value.ShouldBe(7);
+        // Compile the runaway first, so both evaluations are on the worker at once.
+        _ = runner.Shards[0].Current!;
+
+        var victim = runner.RunAsync(Scripts.Vt("spin", Spin, TimeSpan.FromSeconds(20), Ms(5000)), Ct);
+        await Task.Delay(200, Ct);
+        var culprit = await runner.RunAsync(Scripts.Vt("runaway", Runaway, TimeSpan.FromMilliseconds(300)), Ct);
+        culprit.Reason!.ShouldStartWith("script timed out after ");
+
+        var victimOutcome = await victim.WaitAsync(TimeSpan.FromSeconds(15), Ct);
+        victimOutcome.Status.ShouldBe(ScriptRunStatus.Unavailable);
+        victimOutcome.Reason.ShouldBe(ScriptRunOutcome.WorkerRestartedReason);
+        await Scripts.Eventually(() => runner.QuarantinedKeys(ScriptContextKind.VirtualTag).Count == 1, TimeSpan.FromSeconds(5), "the culprit's quarantine");
+        runner.QuarantinedKeys(ScriptContextKind.VirtualTag).ShouldBe(["runaway"]);
+        runner.SuspectKeys.ShouldBeEmpty("a deadline kill is unambiguous: nobody else is suspected");
+        (await runner.RunAsync(Scripts.Vt("spin", Spin, inputs: Ms(0)), Ct)).Value.ShouldBe(0);
+    }
+
+    /// <summary>An allocation bomb dies in its worker (heap hard limit); the host's own memory does not move.</summary>
+    [Fact]
+    public async Task An_allocation_bomb_is_contained_in_its_worker()
+    {
+        await using var runner = Scripts.Runner(Scripts.Options(heapLimit: 128L * 1024 * 1024));
+        (await runner.RunAsync(Scripts.Vt("sibling", Healthy), Ct)).Value.ShouldBe(7);
+
+        GC.Collect();
+        var hostBefore = GC.GetTotalMemory(forceFullCollection: true);
+        var outcome = await runner.RunAsync(Scripts.Vt("bomb",
+            "var hoard = new System.Collections.Generic.List<byte[]>(); while (true) { hoard.Add(new byte[1 << 20]); }",
+            TimeSpan.FromSeconds(10)), Ct);
+        var hostAfter = GC.GetTotalMemory(forceFullCollection: true);
+
+        outcome.Status.ShouldNotBe(ScriptRunStatus.Ok);
+        (hostAfter - hostBefore).ShouldBeLessThan(32L * 1024 * 1024, "the hoard lived in the worker's heap, not the host's");
+        await Scripts.Eventually(() => runner.Shards[0].Current, TimeSpan.FromSeconds(10), "a worker");
+        (await runner.RunAsync(Scripts.Vt("sibling", Healthy), Ct)).Value.ShouldBe(7);
+    }
+
+    /// <summary>Fail closed (design §14 #4): no worker means Bad, never an in-process run.</summary>
+    [Fact]
+    public async Task A_worker_that_cannot_start_reports_unavailable_and_never_runs_in_process()
+    {
+        var missing = Path.Combine(Path.GetTempPath(), "no-such-dir-" + Guid.NewGuid().ToString("N"), OutOfProcessScriptRunner.WorkerAssemblyFileName);
+        await using var runner = Scripts.Runner(Scripts.Options(workerPath: missing, unavailableGrace: TimeSpan.FromSeconds(1)));
+
+        var outcome = await runner.RunAsync(Scripts.Vt("vt", "return 1;"), Ct);
+        outcome.Status.ShouldBe(ScriptRunStatus.Unavailable);
+        outcome.Reason.ShouldBe(ScriptRunOutcome.RunnerUnavailableReason);
+        outcome.ToVirtualTagEvalResult().StatusCode.ShouldBe(ZB.MOM.WW.OtOpcUa.Commons.OpcUa.OpcUaStatus.BadResourceUnavailable);
+        runner.Shards[0].ConsecutiveFailures.ShouldBeGreaterThan(0, "the failed start backs off");
+    }
+
+    /// <summary>A worker whose pipe reaches end of stream exits by itself (the Linux "host died" path, design §3.3).</summary>
+    [Fact]
+    public async Task A_worker_exits_by_itself_when_its_pipe_closes()
+    {
+        await using var runner = Scripts.Runner(Scripts.Options());
+        (await runner.RunAsync(Scripts.Vt("vt", Healthy), Ct)).Value.ShouldBe(7);
+        var worker = runner.Shards[0].Current.ShouldNotBeNull();
+        using var process = Process.GetProcessById(worker.Pid);
+
+        var sw = Stopwatch.StartNew();
+        worker.SeverPipeForTest();
+        await process.WaitForExitAsync(Ct).WaitAsync(TimeSpan.FromSeconds(5), Ct);
+        sw.Elapsed.ShouldBeLessThan(TimeSpan.FromSeconds(2));
+        var exit = await worker.Exited.WaitAsync(TimeSpan.FromSeconds(5), Ct);
+        exit.ExitCode.ShouldBe(ScriptWorkerEnvironment.ExitPipeClosed, "it noticed the EOF; the host did not have to kill it");
+    }
+
+    /// <summary>Design §6: the environment is cleared and repopulated from an allow-list. Positive control first.</summary>
+    [Fact]
+    public async Task The_worker_environment_carries_no_host_secrets()
+    {
+        const string apiKey = "ServerHistorian__ApiKey";
+        const string configDb = "ConnectionStrings__ConfigDb";
+        Environment.SetEnvironmentVariable(apiKey, "sekrit");
+        Environment.SetEnvironmentVariable(configDb, "Server=x;Password=y");
+        try
+        {
+            Environment.GetEnvironmentVariable(apiKey).ShouldBe("sekrit", "positive control: the host has it");
+            await using var runner = Scripts.Runner(Scripts.Options());
+            (await runner.RunAsync(Scripts.Vt("vt", Healthy), Ct)).Value.ShouldBe(7);
+
+            var diag = await runner.Shards[0].Current!.DiagnosticsAsync(TimeSpan.FromSeconds(10));
+            diag.EnvironmentNames.ShouldNotContain(apiKey);
+            diag.EnvironmentNames.ShouldNotContain(configDb);
+            diag.EnvironmentNames.ShouldContain(ScriptWorkerEnvironment.Nonce, "the allow-listed launch variables do arrive");
+            diag.EnvironmentNames.ShouldContain("DOTNET_GCHeapHardLimit");
+            diag.WorkingDirectory.ShouldNotBe(Environment.CurrentDirectory);
+            // An empty per-worker directory under the temp root (macOS reports /var as /private/var, so match the leaf).
+            diag.WorkingDirectory.ShouldContain(Path.Combine("otopcua-scriptworker", "otopcua-sw-"));
+            Directory.EnumerateFileSystemEntries(diag.WorkingDirectory).ShouldBeEmpty();
+        }
+        finally
+        {
+            Environment.SetEnvironmentVariable(apiKey, null);
+            Environment.SetEnvironmentVariable(configDb, null);
+        }
+    }
+
+    /// <summary>Design §6: the host's cluster, database, OPC UA and secrets stacks are not in the worker.</summary>
+    [Fact]
+    public async Task The_worker_loads_none_of_the_host_stacks()
+    {
+        await using var runner = Scripts.Runner(Scripts.Options());
+        (await runner.RunAsync(Scripts.Vt("vt", "return System.Math.Abs(-3);"), Ct)).Value.ShouldBe(3);
+        var diag = await runner.Shards[0].Current!.DiagnosticsAsync(TimeSpan.FromSeconds(10));
+
+        diag.LoadedAssemblies.ShouldContain("ZB.MOM.WW.OtOpcUa.Core.Scripting", "positive control: the compile ran here");
+        diag.LoadedAssemblies.ShouldContain("Microsoft.CodeAnalysis.CSharp");
+        foreach (var prefix in ScriptWorkerEnvironment.ForbiddenAssemblyPrefixes)
+            diag.LoadedAssemblies.ShouldNotContain(a => a.StartsWith(prefix, StringComparison.Ordinal), prefix);
+
+        // Not merely unloaded: Akka is not even deployable beside the worker.
+        var folder = Path.GetDirectoryName(runner.WorkerPath)!;
+        File.Exists(Path.Combine(folder, "ZB.MOM.WW.OtOpcUa.ScriptWorker.dll")).ShouldBeTrue("positive control");
+        File.Exists(Path.Combine(folder, "Akka.dll")).ShouldBeFalse();
+        File.Exists(Path.Combine(folder, "Grpc.Core.Api.dll")).ShouldBeFalse();
+    }
+
+    [Fact]
+    public async Task Script_log_lines_come_back_through_the_invocations_logger()
+    {
+        var sink = new CapturingSink();
+        await using var runner = Scripts.Runner(Scripts.Options());
+        (await runner.RunAsync(Scripts.Vt("vt", "ctx.Logger.Information(\"hello {N}\", 42); return 1;", logger: sink.CreateLogger()), Ct))
+            .Value.ShouldBe(1);
+        await Scripts.Eventually(() => sink.Rendered.Contains("hello 42"), TimeSpan.FromSeconds(5), "the forwarded log line");
+    }
+
+    [Fact]
+    public async Task An_alarm_predicate_runs_out_of_process()
+    {
+        await using var runner = Scripts.Runner(Scripts.Options());
+        var outcome = await runner.RunAsync(new ScriptInvocation("alarm-1", ScriptContextKind.AlarmPredicate,
+            "return (double)ctx.GetTag(\"t\").Value > 50;", Scripts.Input("t", 75.0), TimeSpan.FromSeconds(5)), Ct);
+        outcome.Status.ShouldBe(ScriptRunStatus.Ok, outcome.Reason);
+        outcome.Value.ShouldBe(true);
+    }
+
+    /// <summary>Design §14 #11: an unsupported type is an explicit failure, never a silent conversion.</summary>
+    [Fact]
+    public async Task Unsupported_input_and_result_types_are_explicit_failures()
+    {
+        await using var runner = Scripts.Runner(Scripts.Options());
+        var result = await runner.RunAsync(Scripts.Vt("list", "return new System.Collections.Generic.List<int> { 1 };"), Ct);
+        result.Status.ShouldBe(ScriptRunStatus.Failed);
+        result.Reason!.ShouldStartWith("unsupported type: script returned a value of unsupported type System.Collections.Generic.List");
+
+        var input = await runner.RunAsync(Scripts.Vt("guid", "return 1;", inputs: Scripts.Input("g", Guid.NewGuid())), Ct);
+        input.Status.ShouldBe(ScriptRunStatus.Failed);
+        input.Reason!.ShouldStartWith("unsupported type: input 'g' has a value of unsupported type System.Guid");
+    }
+}

tests/Server/ZB.MOM.WW.OtOpcUa.ScriptWorker.Tests/HandshakeTests.cs

@@ -0,0 +1,86 @@
+using System.IO.Pipes;
+using System.Security.Cryptography;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Scripting.OutOfProcess;
+using ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol;
+using ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol.V1;
+
+namespace ZB.MOM.WW.OtOpcUa.ScriptWorker.Tests;
+
+/// <summary>lmxopcua#780 design §6 "Pipe hardening": only the launched process, echoing its nonce, is accepted.</summary>
+public sealed class HandshakeTests
+{
+    private static CancellationToken Ct => TestContext.Current.CancellationToken;
+
+    private static async Task<Exception?> HandshakeWith(Func<Envelope, Envelope> reply, string expectedNonce = "right", int? expectedPid = 1234)
+    {
+        var name = "otopcua-sw-test-" + Convert.ToHexString(RandomNumberGenerator.GetBytes(6));
+        await using var server = new NamedPipeServerStream(name, PipeDirection.InOut, 1, PipeTransmissionMode.Byte,
+            PipeOptions.Asynchronous | PipeOptions.CurrentUserOnly);
+        await using var client = new NamedPipeClientStream(".", name, PipeDirection.InOut, PipeOptions.Asynchronous | PipeOptions.CurrentUserOnly);
+        var accept = server.WaitForConnectionAsync(Ct);
+        await client.ConnectAsync(TimeSpan.FromSeconds(5), Ct);
+        await accept;
+
+        var rogue = Task.Run(async () =>
+        {
+            var hello = await ScriptWorkerFrameCodec.ReadAsync(client, ScriptWorkerFrameCodec.DefaultMaxFrameBytes, Ct);
+            await ScriptWorkerFrameCodec.WriteAsync(client, reply(hello!), ScriptWorkerFrameCodec.DefaultMaxFrameBytes, Ct);
+            await client.FlushAsync(Ct);
+        }, Ct);
+
+        try
+        {
+            using var timeout = CancellationTokenSource.CreateLinkedTokenSource(Ct);
+            timeout.CancelAfter(TimeSpan.FromSeconds(5));
+            await WorkerConnection.HandshakeAsync(server, new Hello { Nonce = expectedNonce }, expectedNonce, expectedPid, timeout.Token);
+            await rogue;
+            return null;
+        }
+        catch (Exception ex)
+        {
+            return ex;
+        }
+    }
+
+    private static Envelope Ready(string nonce, int pid) => new()
+    {
+        ProtocolVersion = ScriptWorkerFrameCodec.ProtocolVersion,
+        Ready = new Ready { Nonce = nonce, Pid = pid },
+    };
+
+    [Fact]
+    public async Task The_launched_process_echoing_its_nonce_is_accepted()
+        => (await HandshakeWith(_ => Ready("right", 1234))).ShouldBeNull("positive control");
+
+    [Fact]
+    public async Task A_wrong_nonce_is_refused()
+        => (await HandshakeWith(_ => Ready("wrong", 1234))).ShouldBeOfType<ScriptWorkerProtocolException>()
+            .Message.ShouldContain("nonce");
+
+    [Fact]
+    public async Task A_client_that_is_not_the_launched_process_is_refused()
+        => (await HandshakeWith(_ => Ready("right", 999))).ShouldBeOfType<ScriptWorkerProtocolException>()
+            .Message.ShouldContain("pid");
+
+    [Fact]
+    public async Task Anything_but_ready_first_is_refused()
+        => (await HandshakeWith(_ => new Envelope
+        {
+            ProtocolVersion = ScriptWorkerFrameCodec.ProtocolVersion,
+            Heartbeat = new Heartbeat(),
+        })).ShouldBeOfType<ScriptWorkerProtocolException>();
+
+    [Fact]
+    public async Task The_hello_carries_the_nonce_to_echo()
+    {
+        string? seen = null;
+        (await HandshakeWith(hello =>
+        {
+            seen = hello.Hello.Nonce;
+            return Ready(hello.Hello.Nonce, 1234);
+        })).ShouldBeNull();
+        seen.ShouldBe("right");
+    }
+}

tests/Server/ZB.MOM.WW.OtOpcUa.ScriptWorker.Tests/ParityTests.cs

@@ -0,0 +1,95 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Core.Scripting;
+
+namespace ZB.MOM.WW.OtOpcUa.ScriptWorker.Tests;
+
+/// <summary>
+///     lmxopcua#780 design §13 "Parity": the same script, through <see cref="InProcessScriptRunner"/> (today's guard)
+///     and through the worker, gives the same status, reason, value and exact CLR value type.
+/// </summary>
+[Collection(ScriptWorkerCollection.Name)]
+[Trait("Category", "ScriptWorker")]
+public sealed class ParityTests
+{
+    private static CancellationToken Ct => TestContext.Current.CancellationToken;
+
+    public static TheoryData<string, string> Cases() => new()
+    {
+        { "arithmetic", "return 1 + 2;" },
+        { "string", "return \"a\" + ctx.GetTag(\"x\").Value;" },
+        { "throw", "throw new System.InvalidOperationException(\"boom\");" },
+        { "compile error", "return undefinedThing;" },
+        { "sandbox violation", "return System.IO.File.Exists(\"x\");" },
+        { "missing input status", "return ctx.GetTag(\"missing\").StatusCode;" },
+        { "input status", "return ctx.GetTag(\"x\").StatusCode;" },
+        { "source timestamp", "return ctx.GetTag(\"x\").SourceTimestampUtc;" },
+        { "clock", "return ctx.Now > new System.DateTime(2000, 1, 1);" },
+        { "null", "return null;" },
+        { "array", "return new double[] { 1.5, 2.5 };" },
+        { "cast of wrong type", "return (short)ctx.GetTag(\"x\").Value;" },
+    };
+
+    private static readonly IReadOnlyDictionary<string, DataValueSnapshot> Inputs =
+        new Dictionary<string, DataValueSnapshot>(StringComparer.Ordinal)
+        {
+            ["x"] = new DataValueSnapshot(5, 0x40000000u, new DateTime(2026, 1, 2, 3, 4, 5, DateTimeKind.Utc), DateTime.UtcNow),
+        };
+
+    [Theory]
+    [MemberData(nameof(Cases))]
+    public async Task In_and_out_of_process_agree(string name, string source)
+    {
+        using var inProcess = new InProcessScriptRunner();
+        await using var outOfProcess = Scripts.Runner(Scripts.Options());
+        var invocation = Scripts.Vt(name, source, inputs: Inputs);
+
+        var expected = await inProcess.RunAsync(invocation, Ct);
+        var actual = await outOfProcess.RunAsync(invocation, Ct);
+
+        actual.Status.ShouldBe(expected.Status, $"{name}: {actual.Reason} vs {expected.Reason}");
+        actual.Reason.ShouldBe(expected.Reason);
+        Same(actual.Value, expected.Value, name);
+    }
+
+    public static TheoryData<string, object> Typed() => new()
+    {
+        { "bool", true }, { "sbyte", (sbyte)-2 }, { "byte", (byte)2 }, { "short", (short)-3 }, { "ushort", (ushort)3 },
+        { "int", -4 }, { "uint", 4u }, { "long", -5L }, { "ulong", 5UL }, { "float", 1.25f }, { "double", 2.5 },
+        { "string", "s" }, { "System.DateTime", new DateTime(2026, 11, 9, 0, 0, 0, DateTimeKind.Utc) },
+    };
+
+    /// <summary>
+    ///     Unboxing parity (pins design assumption A-7): <c>(T)ctx.GetTag("x").Value</c> works out of process for every
+    ///     tag type, which needs the exact boxed CLR type to survive the wire.
+    /// </summary>
+    [Theory]
+    [MemberData(nameof(Typed))]
+    public async Task Unboxing_to_the_exact_type_matches(string typeName, object value)
+    {
+        using var inProcess = new InProcessScriptRunner();
+        await using var outOfProcess = Scripts.Runner(Scripts.Options());
+        var invocation = Scripts.Vt("unbox-" + typeName, $"var v = ({typeName})ctx.GetTag(\"x\").Value; return v;",
+            inputs: Scripts.Input("x", value));
+
+        var expected = await inProcess.RunAsync(invocation, Ct);
+        var actual = await outOfProcess.RunAsync(invocation, Ct);
+        expected.Status.ShouldBe(ScriptRunStatus.Ok, expected.Reason);
+        actual.Status.ShouldBe(ScriptRunStatus.Ok, actual.Reason);
+        Same(actual.Value, expected.Value, typeName);
+    }
+
+    private static void Same(object? actual, object? expected, string because)
+    {
+        if (expected is null)
+        {
+            actual.ShouldBeNull(because);
+            return;
+        }
+        actual.ShouldNotBeNull(because);
+        actual.GetType().ShouldBe(expected.GetType(), because);
+        if (expected is Array array) ((Array)actual).Cast<object?>().ShouldBe(array.Cast<object?>(), because);
+        else actual.ShouldBe(expected, because);
+    }
+}

tests/Server/ZB.MOM.WW.OtOpcUa.ScriptWorker.Tests/ProtocolTests.cs

@@ -0,0 +1,198 @@
+using System.Buffers.Binary;
+using Google.Protobuf;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Scripting.OutOfProcess;
+using ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol;
+using ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol.V1;
+
+namespace ZB.MOM.WW.OtOpcUa.ScriptWorker.Tests;
+
+/// <summary>lmxopcua#780 design §13 — frame codec and the CLR ↔ Variant mapping.</summary>
+public sealed class ProtocolTests
+{
+    public static IEnumerable<object?[]> Values()
+    {
+        object?[] values =
+        [
+            null, true, false, (sbyte)-5, (byte)250, (short)-3, (ushort)7, -42, 42u, long.MinValue, ulong.MaxValue,
+            1.5f, double.NaN, 3.25, "text", string.Empty, new DateTime(2026, 11, 9, 1, 2, 3, DateTimeKind.Utc),
+            new[] { 1, 2, 3 }, new short[] { -1, 1 }, new[] { "a", "b" }, new[] { true, false }, Array.Empty<double>(),
+            new[] { new DateTime(2020, 1, 1, 0, 0, 0, DateTimeKind.Utc) }, (short)0, 0, 0L, 0.0,
+        ];
+        return values.Select(v => new[] { v });
+    }
+
+    /// <summary>The exact boxed CLR type survives (design §4.4): <c>(short)ctx.GetTag(x).Value</c> must keep working.</summary>
+    [Theory]
+    [MemberData(nameof(Values))]
+    public void Every_type_tag_round_trips_with_its_exact_clr_type(object? value)
+    {
+        VariantCodec.TryEncode(value, out var variant, out var unsupported).ShouldBeTrue();
+        unsupported.ShouldBeNull();
+
+        // Through the wire, not just the object: a payload the serializer drops must still decode.
+        var wire = Variant.Parser.ParseFrom(variant.ToByteArray());
+        var decoded = VariantCodec.Decode(wire);
+
+        if (value is null)
+        {
+            decoded.ShouldBeNull();
+            return;
+        }
+        decoded.ShouldNotBeNull();
+        decoded.GetType().ShouldBe(value.GetType());
+        if (value is Array expected)
+            ((Array)decoded).Cast<object?>().ShouldBe(expected.Cast<object?>());
+        else if (value is double d && double.IsNaN(d))
+            double.IsNaN((double)decoded).ShouldBeTrue();
+        else
+            decoded.ShouldBe(value);
+    }
+
+    [Fact]
+    public void Unsupported_types_are_refused_not_converted()
+    {
+        foreach (var value in new object[] { new List<int> { 1 }, 1.5m, Guid.NewGuid(), new { A = 1 }, new int[1, 1], new object[] { 1 } })
+        {
+            VariantCodec.TryEncode(value, out _, out var type).ShouldBeFalse(value.GetType().Name);
+            type.ShouldNotBeNullOrEmpty();
+        }
+    }
+
+    [Fact]
+    public void Local_datetime_crosses_as_utc()
+    {
+        var local = new DateTime(2026, 6, 1, 12, 0, 0, DateTimeKind.Local);
+        VariantCodec.TryEncode(local, out var variant, out _).ShouldBeTrue();
+        var decoded = (DateTime)VariantCodec.Decode(variant)!;
+        decoded.Kind.ShouldBe(DateTimeKind.Utc);
+        decoded.ShouldBe(local.ToUniversalTime());
+    }
+
+    [Fact]
+    public void A_payload_that_contradicts_its_tag_is_a_protocol_fault()
+    {
+        Should.Throw<ScriptWorkerProtocolException>(() => VariantCodec.Decode(new Variant { Type = Variant.Types.TypeTag.Int16, S = "x" }));
+        Should.Throw<ScriptWorkerProtocolException>(() => VariantCodec.Decode(new Variant { Type = (Variant.Types.TypeTag)99 }));
+        Should.Throw<OverflowException>(() => VariantCodec.Decode(new Variant { Type = Variant.Types.TypeTag.Int16, I = 1 << 20 }));
+    }
+
+    private static Envelope Sample() => new()
+    {
+        ProtocolVersion = ScriptWorkerFrameCodec.ProtocolVersion,
+        Seq = 7,
+        Heartbeat = new Heartbeat { Inflight = 3, HeapBytes = 1234 },
+    };
+
+    [Fact]
+    public async Task A_frame_round_trips()
+    {
+        using var stream = new MemoryStream();
+        await ScriptWorkerFrameCodec.WriteAsync(stream, Sample(), 1024, TestContext.Current.CancellationToken);
+        stream.Position = 0;
+        var read = await ScriptWorkerFrameCodec.ReadAsync(stream, 1024, TestContext.Current.CancellationToken);
+        read.ShouldBe(Sample());
+        (await ScriptWorkerFrameCodec.ReadAsync(stream, 1024, TestContext.Current.CancellationToken)).ShouldBeNull("a clean end of stream at a frame boundary");
+    }
+
+    [Fact]
+    public async Task Oversize_frames_are_refused_on_write_and_on_read()
+    {
+        using var stream = new MemoryStream();
+        await Should.ThrowAsync<ScriptWorkerProtocolException>(async () =>
+            await ScriptWorkerFrameCodec.WriteAsync(stream, Sample(), 4, TestContext.Current.CancellationToken));
+        stream.Length.ShouldBe(0, "nothing is written for a refused frame");
+
+        await ScriptWorkerFrameCodec.WriteAsync(stream, Sample(), 1024, TestContext.Current.CancellationToken);
+        stream.Position = 0;
+        await Should.ThrowAsync<ScriptWorkerProtocolException>(async () =>
+            await ScriptWorkerFrameCodec.ReadAsync(stream, 4, TestContext.Current.CancellationToken));
+    }
+
+    public static TheoryData<string, byte[]> BadFrames()
+    {
+        var good = Sample().ToByteArray();
+        var header = new byte[4];
+        BinaryPrimitives.WriteInt32LittleEndian(header, good.Length);
+        var wrongVersion = new Envelope { ProtocolVersion = 99, Heartbeat = new Heartbeat() }.ToByteArray();
+        var noBody = new Envelope { ProtocolVersion = 1, Seq = 1 }.ToByteArray();
+        return new TheoryData<string, byte[]>
+        {
+            { "zero length", new byte[] { 0, 0, 0, 0 } },
+            { "negative length", new byte[] { 0xFF, 0xFF, 0xFF, 0xFF } },
+            { "truncated header", new byte[] { 5, 0 } },
+            { "truncated body", [.. header, .. good[..^1]] },
+            { "garbage body", [5, 0, 0, 0, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF] },
+            { "wrong protocol version", Frame(wrongVersion) },
+            { "no body", Frame(noBody) },
+        };
+    }
+
+    private static byte[] Frame(byte[] body)
+    {
+        var header = new byte[4];
+        BinaryPrimitives.WriteInt32LittleEndian(header, body.Length);
+        return [.. header, .. body];
+    }
+
+    [Theory]
+    [MemberData(nameof(BadFrames))]
+    public async Task Malformed_frames_are_protocol_faults(string why, byte[] bytes)
+    {
+        using var stream = new MemoryStream(bytes);
+        await Should.ThrowAsync<ScriptWorkerProtocolException>(async () =>
+            await ScriptWorkerFrameCodec.ReadAsync(stream, 1024, TestContext.Current.CancellationToken), why);
+    }
+
+    /// <summary>Random bytes never escape as anything but a protocol fault (or a clean end of stream).</summary>
+    [Fact]
+    public async Task Fuzzed_input_only_ever_yields_a_protocol_fault()
+    {
+        var random = new Random(780);
+        for (var i = 0; i < 3000; i++)
+        {
+            var bytes = new byte[random.Next(0, 64)];
+            random.NextBytes(bytes);
+            if (bytes.Length >= 4 && random.Next(2) == 0)
+                BinaryPrimitives.WriteInt32LittleEndian(bytes, random.Next(1, bytes.Length));
+            using var stream = new MemoryStream(bytes);
+            try
+            {
+                while (await ScriptWorkerFrameCodec.ReadAsync(stream, 1024, TestContext.Current.CancellationToken) is { } envelope)
+                {
+                    // A frame that parses must still decode its variants without an unexpected exception type.
+                    if (envelope.BodyCase == Envelope.BodyOneofCase.Results)
+                        foreach (var r in envelope.Results.Items)
+                            try { VariantCodec.Decode(r.Value); } catch (Exception ex) when (ex is ScriptWorkerProtocolException or OverflowException) { }
+                }
+            }
+            catch (ScriptWorkerProtocolException)
+            {
+            }
+        }
+    }
+
+    [Fact]
+    public void Backoff_doubles_from_250ms_to_a_30s_cap_with_20_percent_jitter()
+    {
+        WorkerShard.NextBackoff(1, 0.5).ShouldBe(TimeSpan.FromMilliseconds(250));
+        WorkerShard.NextBackoff(2, 0.5).ShouldBe(TimeSpan.FromMilliseconds(500));
+        WorkerShard.NextBackoff(3, 0.5).ShouldBe(TimeSpan.FromSeconds(1));
+        WorkerShard.NextBackoff(20, 0.5).ShouldBe(TimeSpan.FromSeconds(30));
+        WorkerShard.NextBackoff(1, 0).ShouldBe(TimeSpan.FromMilliseconds(200));
+        WorkerShard.NextBackoff(1, 0.9999999).TotalMilliseconds.ShouldBe(300, tolerance: 0.01);
+        WorkerShard.NextBackoff(40, 1).ShouldBe(TimeSpan.FromSeconds(36));
+    }
+
+    [Fact]
+    public void Shard_placement_is_stable_and_in_range()
+    {
+        // FNV-1a, not string.GetHashCode (randomised per process): a script stays on its shard across restarts.
+        OutOfProcessScriptRunner.ShardIndex("1:vt-1", 2).ShouldBe(OutOfProcessScriptRunner.ShardIndex("1:vt-1", 2));
+        var spread = Enumerable.Range(0, 400).Select(i => OutOfProcessScriptRunner.ShardIndex($"1:vt-{i}", 4)).ToArray();
+        spread.ShouldAllBe(i => i >= 0 && i < 4);
+        spread.Distinct().Count().ShouldBe(4);
+        OutOfProcessScriptRunner.ShardIndex("abc", 1000).ShouldBe((int)(0x1A47E90Bu % 1000));
+    }
+}

tests/Server/ZB.MOM.WW.OtOpcUa.ScriptWorker.Tests/SeamEndToEndTests.cs

@@ -0,0 +1,88 @@
+using System.Collections.Concurrent;
+using System.Diagnostics;
+using Serilog;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Core.Scripting;
+using ZB.MOM.WW.OtOpcUa.Driver.Calculation;
+
+namespace ZB.MOM.WW.OtOpcUa.ScriptWorker.Tests;
+
+/// <summary>
+///     lmxopcua#780 — the whole path a client sees: a real Calculation driver whose seam runs out of process on the real
+///     worker. A script failure publishes <c>BadInternalError</c> as today; the worker dying under a script publishes
+///     <c>BadResourceUnavailable</c> (0x80040000), the ScadaBridge-visible code; and the tag recovers Good afterwards.
+/// </summary>
+[Collection(ScriptWorkerCollection.Name)]
+[Trait("Category", "ScriptWorker")]
+public sealed class SeamEndToEndTests
+{
+    private const uint StatusGood = 0u;
+    private const uint StatusBadInternalError = 0x80020000u;
+    private const uint StatusBadResourceUnavailable = 0x80040000u;
+    private const string Tag = "calc/e/spin";
+
+    /// <summary>Spins for <c>src/ms</c> milliseconds, throws when it is negative, and returns it otherwise.</summary>
+    private const string Script =
+        "var ms = (double)ctx.GetTag(\"src/ms\").Value; if (ms < 0) throw new System.InvalidOperationException(\"negative\"); " +
+        "var end = ctx.Now.AddMilliseconds(ms); while (ctx.Now < end) { } return ms;";
+
+    private static CancellationToken Ct => TestContext.Current.CancellationToken;
+
+    private static async Task Settle(CalculationDriver driver)
+    {
+        var deadline = DateTime.UtcNow + TimeSpan.FromSeconds(60);
+        while (DateTime.UtcNow < deadline && !driver.IsEvaluationIdle) await Task.Delay(10);
+        driver.IsEvaluationIdle.ShouldBeTrue();
+    }
+
+    [Fact]
+    public async Task A_calculation_tag_publishes_BadResourceUnavailable_only_when_the_worker_died_under_it()
+    {
+        await using var runner = Scripts.Runner(Scripts.Options());
+        var json = $"{{\"scriptId\":\"s\",\"changeTriggered\":true,\"scriptSource\":{System.Text.Json.JsonSerializer.Serialize(Script)}}}";
+        var driver = new CalculationDriver(
+            new CalculationDriverOptions { RawTags = [new RawTagEntry(Tag, json, WriteIdempotent: false)], RunTimeout = TimeSpan.FromSeconds(20), ScriptRunner = runner },
+            "calc-drv", new ScriptRootLogger(new LoggerConfiguration().CreateLogger()));
+        var published = new ConcurrentQueue<DataChangeEventArgs>();
+        driver.OnDataChange += (_, e) => published.Enqueue(e);
+        await driver.InitializeAsync("{}", Ct);
+
+        driver.OnDependencyValue("src/ms", 0.0, StatusGood, DateTime.UtcNow);
+        await Settle(driver);
+        published.TryDequeue(out var good).ShouldBeTrue();
+        good!.Snapshot.StatusCode.ShouldBe(StatusGood);
+        good.Snapshot.Value.ShouldBe(0.0);
+
+        // A script fault: BadInternalError, exactly as in process.
+        driver.OnDependencyValue("src/ms", -1.0, StatusGood, DateTime.UtcNow);
+        await Settle(driver);
+        published.TryDequeue(out var threw).ShouldBeTrue();
+        threw!.Snapshot.StatusCode.ShouldBe(StatusBadInternalError);
+
+        driver.OnDependencyValue("src/ms", 1.0, StatusGood, DateTime.UtcNow);
+        await Settle(driver);
+        published.TryDequeue(out var back).ShouldBeTrue();
+        back!.Snapshot.StatusCode.ShouldBe(StatusGood);
+
+        // The worker dies under a run: the runner, not the script, failed.
+        driver.OnDependencyValue("src/ms", 5000.0, StatusGood, DateTime.UtcNow);
+        var worker = await Scripts.Eventually(() => runner.Shards[0].Current is { InFlightCount: 1 } w ? w : null,
+            TimeSpan.FromSeconds(10), "the run in flight");
+        await Task.Delay(200, Ct);
+        Process.GetProcessById(worker.Pid).Kill();
+        await Settle(driver);
+        published.TryDequeue(out var unavailable).ShouldBeTrue();
+        unavailable!.Snapshot.StatusCode.ShouldBe(StatusBadResourceUnavailable);
+        unavailable.Snapshot.Value.ShouldBe(1.0, "the last good value rides out with the Bad status");
+
+        // Recovery: the next trigger runs (in the isolation worker, as a suspect) and publishes Good.
+        driver.OnDependencyValue("src/ms", 2.0, StatusGood, DateTime.UtcNow);
+        await Settle(driver);
+        published.TryDequeue(out var recovered).ShouldBeTrue();
+        recovered!.Snapshot.StatusCode.ShouldBe(StatusGood);
+        recovered.Snapshot.Value.ShouldBe(2.0);
+        await driver.ShutdownAsync(Ct);
+    }
+}

tests/Server/ZB.MOM.WW.OtOpcUa.ScriptWorker.Tests/TestSupport.cs

@@ -0,0 +1,82 @@
+using System.Collections.Concurrent;
+using Serilog;
+using Serilog.Core;
+using Serilog.Events;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Core.Scripting;
+using ZB.MOM.WW.OtOpcUa.Core.Scripting.OutOfProcess;
+
+namespace ZB.MOM.WW.OtOpcUa.ScriptWorker.Tests;
+
+/// <summary>Collects Serilog events in memory.</summary>
+internal sealed class CapturingSink : ILogEventSink
+{
+    public ConcurrentQueue<LogEvent> Events { get; } = new();
+
+    public void Emit(LogEvent logEvent) => Events.Enqueue(logEvent);
+
+    public ILogger CreateLogger() => new LoggerConfiguration().MinimumLevel.Verbose().WriteTo.Sink(this).CreateLogger();
+
+    public IEnumerable<string> Rendered => Events.Select(e => e.RenderMessage());
+}
+
+internal static class Scripts
+{
+    public static readonly IReadOnlyDictionary<string, DataValueSnapshot> NoInputs =
+        new Dictionary<string, DataValueSnapshot>(StringComparer.Ordinal);
+
+    public static IReadOnlyDictionary<string, DataValueSnapshot> Input(string path, object? value, uint status = 0)
+        => new Dictionary<string, DataValueSnapshot>(StringComparer.Ordinal)
+        {
+            [path] = new DataValueSnapshot(value, status, DateTime.UtcNow, DateTime.UtcNow),
+        };
+
+    public static ScriptInvocation Vt(string key, string source, TimeSpan? timeout = null,
+        IReadOnlyDictionary<string, DataValueSnapshot>? inputs = null, ILogger? logger = null)
+        => new(key, ScriptContextKind.VirtualTag, source, inputs ?? NoInputs, timeout ?? TimeSpan.FromSeconds(5), logger);
+
+    /// <summary>Options for a single-shard runner with short budgets, so the containment tests run in seconds.</summary>
+    public static ScriptingOptions Options(int shards = 1, TimeSpan? hardGrace = null, int quarantineAfterKills = 2,
+        int probation = 20, TimeSpan? unavailableGrace = null, string? workerPath = null, long heapLimit = 256L * 1024 * 1024)
+        => new()
+        {
+            Runner = ScriptRunnerMode.OutOfProcess,
+            QuarantineAfterConsecutiveTimeouts = 100,
+            Worker = new ScriptWorkerOptions
+            {
+                Shards = shards,
+                HardGrace = hardGrace ?? TimeSpan.FromMilliseconds(500),
+                QuarantineAfterKills = quarantineAfterKills,
+                IsolationProbationRuns = probation,
+                UnavailableGrace = unavailableGrace ?? TimeSpan.FromSeconds(30),
+                ExecutablePath = workerPath,
+                HeapLimitBytes = heapLimit,
+            },
+        };
+
+    public static OutOfProcessScriptRunner Runner(ScriptingOptions options, ILogger? log = null)
+        => new(options, log ?? new LoggerConfiguration().CreateLogger(), null,
+            heartbeatInterval: TimeSpan.FromSeconds(1), loadTimeout: TimeSpan.FromSeconds(60));
+
+    public static async Task<T> Eventually<T>(Func<T?> probe, TimeSpan timeout, string what) where T : class
+    {
+        var deadline = DateTime.UtcNow + timeout;
+        while (DateTime.UtcNow < deadline)
+        {
+            if (probe() is { } value) return value;
+            await Task.Delay(20);
+        }
+        throw new TimeoutException($"timed out waiting for {what}");
+    }
+
+    public static async Task Eventually(Func<bool> probe, TimeSpan timeout, string what)
+    {
+        var deadline = DateTime.UtcNow + timeout;
+        while (DateTime.UtcNow < deadline)
+        {
+            if (probe()) return;
+            await Task.Delay(20);
+        }
+        throw new TimeoutException($"timed out waiting for {what}");
+    }
+}

tests/Server/ZB.MOM.WW.OtOpcUa.ScriptWorker.Tests/ZB.MOM.WW.OtOpcUa.ScriptWorker.Tests.csproj

@@ -0,0 +1,30 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <IsPackable>false</IsPackable>
+        <IsTestProject>true</IsTestProject>
+        <RootNamespace>ZB.MOM.WW.OtOpcUa.ScriptWorker.Tests</RootNamespace>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <PackageReference Include="xunit.v3"/>
+        <PackageReference Include="Shouldly"/>
+        <PackageReference Include="Microsoft.NET.Test.Sdk"/>
+        <PackageReference Include="xunit.runner.visualstudio">
+            <PrivateAssets>all</PrivateAssets>
+            <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+        </PackageReference>
+    </ItemGroup>
+
+    <ItemGroup>
+        <ProjectReference Include="..\..\..\src\Core\ZB.MOM.WW.OtOpcUa.Core.Scripting\ZB.MOM.WW.OtOpcUa.Core.Scripting.csproj"/>
+        <ProjectReference Include="..\..\..\src\Core\ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol\ZB.MOM.WW.OtOpcUa.Core.Scripting.Protocol.csproj"/>
+        <ProjectReference Include="..\..\..\src\Core\ZB.MOM.WW.OtOpcUa.Core.Scripting.OutOfProcess\ZB.MOM.WW.OtOpcUa.Core.Scripting.OutOfProcess.csproj"/>
+        <!-- End-to-end seam test: a real Calculation driver over the real worker. -->
+        <ProjectReference Include="..\..\..\src\Drivers\ZB.MOM.WW.OtOpcUa.Driver.Calculation\ZB.MOM.WW.OtOpcUa.Driver.Calculation.csproj"/>
+    </ItemGroup>
+
+    <!-- The real worker, built and placed in script-worker/ beside the tests, exactly as beside the Host. -->
+    <Import Project="..\..\..\src\Server\ZB.MOM.WW.OtOpcUa.ScriptWorker\build\ScriptWorker.Deploy.targets"/>
+
+</Project>