Merge hw6-665 (#665 delete the dead in-place ApplyDelta seam)

Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe

CLAUDE.md

@@ -1161,16 +1161,16 @@ host logger factory (wired in `DriverFactoryBootstrap`; the FOCAS and TwinCAT fa
   first release the prior device/session state (cancel, ≤ 5 s join, dispose — incl. the AbCip alarm projection;
   FOCAS's is PAUSED, its told record kept, #647) — the device-state half of `ShutdownAsync` only; the poll engine is kept and the actor re-subscribes
   after every successful init. AbCip publishes fresh tag tables by reference swap (a second init used to throw
-  "tag name collision" on `AdoptConfigDuringInit`); S7 swaps `Plc` under `_gate`.
+  "tag name collision"); S7 swaps `Plc` under `_gate`.
 - **Data and alarm subscriptions are independent in `DriverInstanceActor` (#662):** a data re-subscribe (every
   deploy's bulk push to a kept driver) detaches DATA only (`DetachDataSubscription`) — it used to unhook
   `OnAlarmEvent` too, silently killing the native-alarm feed until a respawn. The health-poll reconcile
   re-attaches/re-subscribes alarms as well as data, so a failed alarm subscribe is retried every tick.
-  A Connected in-place `ApplyDelta` (unreachable from deploys since #516) releases both subscriptions at the
-  driver, reinitialises, then re-subscribes both (#663) — it used to keep handles the reinit had invalidated.
-  A mid-connect `ApplyDelta` re-runs `InitializeAsync(newConfig)`, so **every driver's `InitializeAsync` must adopt a
-  config with a body** — Calculation now does, Galaxy (no hot-swap) now refuses a non-equivalent one, and the actor
-  sends `DeltaApplied` once the adopted init succeeds (#664).
+- **A config change is a respawn — there is NO in-place path (#665).** The `ApplyDelta`/`ApplyResult`/`DeltaApplied`
+  seam (host `ApplyChildDelta`, `DriverSpawnPlan.ToApplyDelta`, the actor's Connected reinit and mid-connect
+  `AdoptConfigDuringInit`) was unreachable since #516 and is deleted; #663/#664 were latent bugs in it. `IDriver.ReinitializeAsync`
+  stays as a per-driver contract the runtime never calls. Every driver's `InitializeAsync` still serves the config it is
+  handed (Calculation adopts, Galaxy refuses a non-equivalent one — #664), and still releases prior state (#630).
   `docs/DriverLifecycle.md`.
 - **S7 (#632/#638):** STRING/WSTRING/CHAR/WCHAR and DTL/DATE/TOD/TIME/S5TIME codecs (`S7ValueCodecs`; TOD/TIME/S5TIME
   surface as Int32 ms); an undecodable buffer or unrepresentable write is `BadOutOfRange` with no health impact.

docs/DriverLifecycle.md

@@ -255,25 +255,15 @@ Things to know before touching any of this:
   instead of gating the feed for the life of the connection. OpcUaClient removes a half-built alarm
   subscription from its session when the subscribe throws, so those retries do not accumulate.
   End-to-end pin: `NativeAlarmFeedSurvivesDeployTests`.
-- **An in-place `ApplyDelta` on a Connected driver releases and re-establishes BOTH subscriptions (#663).**
-  `ReinitializeAsync` drops every driver-side subscription (#630), but the handler used to keep the actor's
-  handles, and the reconcile only re-subscribes a *missing* handle — so the driver went silent until a
-  reconnect. It now releases data and alarms at the driver first (explicitly, so a driver whose reinit keeps
-  its subscriptions is not left holding two), reinitialises, and re-subscribes both in a `finally` (a failed
-  reinit has lost them too). It stays on `ReinitializeAsync` rather than shutdown + initialise because
-  Calculation and Galaxy take their config at construction and ignore the JSON passed to `InitializeAsync`.
-  Not reachable from a deploy since #516 (a DriverConfig change respawns). Pin:
-  `An_in_place_ApplyDelta_leaves_one_live_data_and_one_live_alarm_subscription` (one case per wrong fix).
-- **A mid-connect `ApplyDelta` re-runs `InitializeAsync(newConfig)` — so every driver's `InitializeAsync` must
-  honour the JSON (#664).** `AdoptConfigDuringInit` adopts a delta that lands while Connecting/Reconnecting by
-  re-initialising, and acks on adoption. Every driver re-parses a config with a body (#516/#630) except two that
-  used to ignore it: **Calculation** now rebuilds its tag table from it (sharing `AdoptConfig` with
-  `ReinitializeAsync`, and disposing any running timer scheduler first), and **Galaxy**, which cannot hot-swap
-  its options, now **refuses** a non-equivalent config with the same `NotSupportedException` its
-  `ReinitializeAsync` throws — it used to connect on the old endpoint while the deploy reported success. A
-  `"{}"`/empty document still keeps the constructor options. Once the adopted init succeeds the actor sends
-  `DeltaApplied`, so the host re-registers a dependency consumer's mux interest — the mid-connect path used to
-  send nothing. A new driver must follow the same rule. Unreachable from a deploy since #516.
+- **There is no in-place config path — a config change is a respawn (#665).** Since #516 any DriverConfig,
+  DriverType or ResilienceConfig change is stop + respawn, so the factory is the single parse authority. The old
+  in-place seam (host `ApplyChildDelta` → actor `ApplyDelta` → `ReinitializeAsync`, plus the mid-connect
+  `AdoptConfigDuringInit`, `ApplyResult` and `DeltaApplied`) had no producer and was deleted after two latent
+  bugs were found in it: a Connected reinit kept subscription handles the driver had dropped (#663), and the
+  mid-connect path re-ran `InitializeAsync(newConfig)` on two drivers that ignored the JSON (#664). Kept from that
+  work: Calculation's `InitializeAsync` adopts a config with a body and Galaxy's refuses a non-equivalent one,
+  because the `IDriver` contract is that a driver serves the document it is handed. `ReinitializeAsync` stays as a
+  per-driver contract the runtime does not call.
 - **Restart tests must assert a FUNCTION, never existence.** `RestartDriver_respawns_the_child_without_an_actor_name_collision`
   asserts only that a child exists after a restart, and it passed green against the dead driver 03/S16
   describes. It is kept — its own subject, the `InvalidActorNameException`, is real — but the load-bearing
@@ -458,8 +448,8 @@ have leaked ~360 transports at the 10 s retry interval. The shutdown is best-eff
 on it still gets its initialise attempt.
 
 **`InitializeAsync` itself releases the previous device/connection state first (#630).** The retry above is not
-the only way in: `DriverInstanceActor.AdoptConfigDuringInit` calls `InitializeAsync` on a live driver with *no*
-teardown, so a driver that does `_devices[host] = new DeviceState(...)` (or `Session = ...`, `Plc = ...`) orphans
+the only way in: the `IDriver` contract allows `InitializeAsync` on a live driver with *no* teardown, and a retry
+tick can overlap a still-running attempt, so a driver that does `_devices[host] = new DeviceState(...)` (or `Session = ...`, `Plc = ...`) orphans
 the previous state's probe / recycle / fixed-tree loops and its client. FOCAS, AbLegacy, AbCip, TwinCAT, S7 and
 OpcUaClient now cancel, bounded-join (5 s) and dispose that state at the top of `InitializeAsync`
 (`ReleaseDeviceStatesAsync` / `ReleaseConnectionAsync` / `ReleaseSessionAsync`), alongside Modbus and MQTT.

docs/IncrementalSync.md

@@ -16,9 +16,9 @@ changes the served address space — the **deploy artifact** — and one advisor
    check (`FetchAndCache`) — see `docs/Configuration.md` §`ConfigSource`.
 3. **Apply.** `DriverHostActor` (`src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Drivers/`) opens the artifact and
    reconciles in two halves:
-   - **Drivers** — `DriverSpawnPlanner.Compute` yields `ToStop` / `ToApplyDelta` / `ToSpawn`. A changed
-     driver config reaches the live driver as `IDriver.ReinitializeAsync` on its `DriverInstanceActor`;
-     a removed driver is stopped. An unreadable or empty blob is "no answer": the apply fails and the
+   - **Drivers** — `DriverSpawnPlanner.Compute` yields `ToStop` / `ToSpawn`. A changed
+     driver config (DriverConfig, DriverType or ResilienceConfig) is a stop + respawn (#516) — there is no
+     in-place path (#665 deleted the unreachable `ApplyDelta` seam); a removed driver is stopped. An unreadable or empty blob is "no answer": the apply fails and the
      running children are left alone (never an empty configuration).
    - **Address space** — `AddressSpaceComposer` builds an `AddressSpaceComposition` from the artifact;
      `AddressSpacePlan` diffs it against the last applied composition; `AddressSpaceChangeClassifier`

docs/drivers/Mqtt.md

@@ -415,7 +415,7 @@ down rather than swallowing it. A SUBACK failure degrades just the affected RawP
 There are **two** kinds of reconnect and only one of them fires that callback. A drop the connection's
 own supervisor recovers keeps the same `MqttConnection`, so `Reconnected` → `OnReconnectedAsync`
 re-establishes every live filter. A **session rebuild** — `ShutdownAsync` + `InitializeAsync` (the #527
-comms-loss watchdog's retry path, and an `ApplyDelta` that changes the endpoint or credentials) — builds
+comms-loss watchdog's retry path, and a `ReinitializeAsync` that changes the endpoint or credentials) — builds
 a *new* connection and re-attaches the *same* `MqttSubscriptionManager`, and the re-subscribe then comes
 from the host (`DriverInstanceActor.ResubscribeDesired`) rather than from the callback. `AttachTo`
 therefore **forgets the filters the previous session had established**: the dedupe set is a claim about

docs/v2/Runtime.md

@@ -78,7 +78,7 @@ Per-driver-instance child. State machine:
 
 `ShouldStub(driverType, roles)` returns `true` for `"Galaxy" | "Historian.Wonderware"` on non-Windows; the actor goes straight to `Stubbed` and returns deterministic success without touching real hardware. Wiring this into the DriverHost child-spawn path is follow-up F20 (folds into F7).
 
-Engine wiring (subscription publishing, ApplyDelta diff, bad-quality-on-disconnect, write path, supervisor backoff) is stubbed — tracked as F7. Tests exercise message contracts, not engine behaviour.
+Engine wiring (subscription publishing, config-change diff, bad-quality-on-disconnect, write path, supervisor backoff) is stubbed — tracked as F7. Tests exercise message contracts, not engine behaviour.
 
 ## VirtualTagActor / ScriptedAlarmActor
 

src/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions/IDriver.cs

@@ -24,8 +24,9 @@ public interface IDriver
 
     /// <summary>
     ///     Apply a config change in place without tearing down the driver process.
-    ///     Invoked by the v2 <c>DriverInstanceActor</c> when ApplyDelta reports that only this
-    ///     driver's config changed in the new deployment.
+    ///     <para>The runtime does not call this today: since #516 a DriverConfig change is a stop + respawn,
+    ///     and #665 deleted <c>DriverInstanceActor</c>'s in-place <c>ApplyDelta</c> path. Kept as the in-place
+    ///     contract each driver implements and tests.</para>
     /// </summary>
     /// <remarks>
     ///     Per <c>docs/v2/driver-stability.md</c> §"In-process only (Tier A/B)" — Reinitialize is the

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip/AbCipDriver.cs

@@ -360,8 +360,8 @@ public sealed class AbCipDriver : IDriver, IReadable, IWritable, ITagDiscovery,
     /// <inheritdoc />
     public async Task InitializeAsync(string driverConfigJson, CancellationToken cancellationToken)
     {
-        // #630: InitializeAsync is reachable on a live driver (DriverInstanceActor.AdoptConfigDuringInit
-        // runs it with no teardown first). Release the previous device states' probe loops + handles before
+        // #630: InitializeAsync is reachable on a live driver with no teardown first (the IDriver contract
+        // allows it, and a reconnect retry can overlap a running attempt). Release the previous device states' probe loops + handles before
         // the overwrite below. Deliberately NOT ShutdownAsync: that also drops _poll and the subscriptions.
         await ReleaseDeviceStatesAsync(cancellationToken).ConfigureAwait(false);
         _health = new DriverHealth(DriverState.Initializing, null, null);

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/AbLegacyDriver.cs

@@ -145,8 +145,8 @@ public sealed class AbLegacyDriver : IDriver, IReadable, IWritable, ITagDiscover
     /// <inheritdoc />
     public async Task InitializeAsync(string driverConfigJson, CancellationToken cancellationToken)
     {
-        // #630: InitializeAsync can run on a live driver (DriverInstanceActor.AdoptConfigDuringInit calls it
-        // without a teardown first). Release the previous device states' probe loops + runtimes BEFORE the
+        // #630: InitializeAsync can run on a live driver without a teardown first (the IDriver contract
+        // allows it, and a reconnect retry can overlap a running attempt). Release the previous device states' probe loops + runtimes BEFORE the
         // overwrite below, or they are orphaned beyond the reach of ShutdownAsync. Deliberately NOT
         // ShutdownAsync: that also drops _poll and every subscription, which are owned by the shutdown path (the actor re-subscribes after every successful init).
         await ReleaseDeviceStatesAsync().ConfigureAwait(false);

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

@@ -67,7 +67,7 @@ public sealed class CalculationDriver : IDriver, IDependencyConsumer, ISubscriba
 
     // Authored calc tags, keyed by RawPath (identity + evaluation id). Built at construction so
     // DependencyRefs is available BEFORE InitializeAsync (the host reads it when spawning the mux-adapter),
-    // and REBUILT on every ReinitializeAsync (an in-place ApplyDelta re-binds an edited calc-tag set).
+    // and REBUILT on every ReinitializeAsync / body-carrying InitializeAsync (an in-place re-bind of an edited calc-tag set).
     private readonly Dictionary<string, CalculationTagDefinition> _tagsByRawPath = new(StringComparer.Ordinal);
 
     // rawPath (a dependency) → the calc tags that read it AND are change-triggered. Drives OnDependencyValue.
@@ -139,7 +139,7 @@ public sealed class CalculationDriver : IDriver, IDependencyConsumer, ISubscriba
     ///     (Re)build the authored tag table (<see cref="_tagsByRawPath"/>), the change-trigger fan-out
     ///     (<see cref="_changeDependents"/>), the dependency-ref interest set (<see cref="_dependencyRefs"/>),
     ///     and the per-tag state map (<see cref="_stateByRawPath"/>) from <paramref name="config"/>. Called
-    ///     once at construction AND on every <see cref="ReinitializeAsync"/> so an in-place ApplyDelta — a
+    ///     once at construction AND on every <see cref="ReinitializeAsync"/> so an in-place config change — a
     ///     calc-tag add/remove/edit, or a script-source edit — actually takes effect. Extracted so the ctor
     ///     and reinit paths share ONE construction routine and cannot drift.
     ///     <para>Per-tag <see cref="TagState"/> is preserved for a tag that survives the edit (cheap last-known
@@ -200,7 +200,7 @@ public sealed class CalculationDriver : IDriver, IDependencyConsumer, ISubscriba
     }
 
     // Reinit config-bind options — mirrors the factory's bind (case-insensitive, enum-string, trailing-comma
-    // tolerant) so an ApplyDelta payload re-binds identically to the spawn payload.
+    // tolerant) so an in-place config payload re-binds identically to the spawn payload.
     private static readonly JsonSerializerOptions ReinitJsonOptions = new()
     {
         PropertyNameCaseInsensitive = true,
@@ -209,8 +209,8 @@ public sealed class CalculationDriver : IDriver, IDependencyConsumer, ISubscriba
         Converters = { new JsonStringEnumConverter() },
     };
 
-    /// <summary>Re-bind the authored raw calc tags from a new merged DriverConfig JSON (the ApplyDelta
-    /// payload). The ctor-fixed <see cref="CalculationEvaluator"/> timeout is kept — <c>RunTimeout</c> is bound
+    /// <summary>Re-bind the authored raw calc tags from a new merged DriverConfig JSON (an in-place
+    /// config payload). The ctor-fixed <see cref="CalculationEvaluator"/> timeout is kept — <c>RunTimeout</c> is bound
     /// at spawn (a change to it is out of this in-place path's scope). A parse failure logs and keeps the
     /// current tags so a malformed delta can never blank the driver.</summary>
     private CalculationDriverOptions ParseOptions(string driverConfigJson)
@@ -287,8 +287,8 @@ public sealed class CalculationDriver : IDriver, IDependencyConsumer, ISubscriba
 
     /// <inheritdoc />
     /// <remarks>
-    ///     #664: <c>InitializeAsync</c> is reachable on a LIVE driver — <c>DriverInstanceActor.AdoptConfigDuringInit</c>
-    ///     re-runs it with a NEW config when an ApplyDelta lands mid-connect — so it adopts a config carrying a
+    ///     #664: <c>InitializeAsync</c> takes a config document and the <see cref="IDriver"/> contract is that the
+    ///     driver serves it (the runtime's mid-connect adoption path was deleted in #665) — so it adopts a config carrying a
     ///     real body (the #516 convention every other driver follows), and disposes any running timer scheduler
     ///     before arming a fresh one (#630: re-initialise without teardown must not leak). A <c>"{}"</c> / empty
     ///     document keeps the constructor-supplied tags, as unit tests rely on.
@@ -308,14 +308,10 @@ public sealed class CalculationDriver : IDriver, IDependencyConsumer, ISubscriba
     /// <inheritdoc />
     public Task ReinitializeAsync(string driverConfigJson, CancellationToken cancellationToken)
     {
-        // A calc-tag add/remove/edit — or a script edit that changes the injected scriptSource — changes the
-        // merged DriverConfig, which DriverSpawnPlanner routes to an in-place ApplyDelta → THIS call (a
-        // respawn fires only on a DriverType/ResilienceConfig change). So the authored tag table is NOT
-        // fixed at construction: we re-bind the new config and REBUILD the tag table + dependency-ref set
-        // here. Without this, added tags never compute, removed tags keep publishing, and edited scripts
-        // serve stale results (deploy reports success but nothing changed). After the rebuild _dependencyRefs
-        // reflects the new authored tags, and the host re-registers the mux interest post-reinit (the
-        // DriverInstanceActor.DeltaApplied → DriverHostActor path, sequenced AFTER this completes).
+        // An in-place config change: re-bind the new config and REBUILD the tag table + dependency-ref set, so
+        // added tags compute, removed tags stop publishing and edited scripts serve the new result. The runtime
+        // itself applies a DriverConfig change by respawning (#516/#665), where a fresh driver registers its
+        // new dependency refs on construction; this path keeps the IDriver contract honest for any caller.
         StopTimers();
         AdoptConfig(driverConfigJson);
         // Re-arm timers off the rebuilt tag set.

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/FocasDriver.cs

@@ -196,8 +196,8 @@ public sealed class FocasDriver : IDriver, IReadable, IWritable, ITagDiscovery,
     /// <returns>A completed task.</returns>
     public async Task InitializeAsync(string driverConfigJson, CancellationToken cancellationToken)
     {
-        // #630: release the previous device states' loops + clients BEFORE they are overwritten (the actor's
-        // AdoptConfigDuringInit calls this without a teardown first). Not ShutdownAsync: that also drops _poll
+        // #630: release the previous device states' loops + clients BEFORE they are overwritten (a live driver can be
+        // re-initialised without a teardown first). Not ShutdownAsync: that also drops _poll
         // and subscriptions, which are owned by the shutdown path (the actor re-subscribes after every successful init).
         await ReleaseDeviceStatesAsync().ConfigureAwait(false);
         ResetAlarmHealth();

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/GalaxyDriver.cs

@@ -349,8 +349,8 @@ public sealed class GalaxyDriver
 
     /// <inheritdoc />
     /// <remarks>
-    ///     #664: <c>InitializeAsync</c> is reachable on a live driver with a NEW config —
-    ///     <c>DriverInstanceActor.AdoptConfigDuringInit</c> re-runs it when an ApplyDelta lands mid-connect. The
+    ///     #664: <c>InitializeAsync</c> takes a config document, and the <see cref="IDriver"/> contract is that a
+    ///     driver serves the one it is handed (the runtime's own mid-connect adoption path was deleted in #665). The
     ///     driver cannot hot-swap its options (they shape the gw session; see <see cref="ReinitializeAsync"/>), so a
     ///     non-equivalent config with a real body is REFUSED here too rather than silently ignored — the driver
     ///     would otherwise connect on its old endpoint while the deploy reported the change applied. A

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect/MTConnectDriver.cs

@@ -21,11 +21,11 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.MTConnect;
 ///         Agent. Every connection is owned by <see cref="InitializeAsync"/>.
 ///     </para>
 ///     <para>
-///         <b>The <c>driverConfigJson</c> argument is honoured, not decorative.</b> The runtime hands
-///         a config change to a <i>live</i> instance — <c>DriverInstanceActor</c>'s <c>ApplyDelta</c>
-///         calls <see cref="ReinitializeAsync"/> with the new document and never rebuilds the object
-///         — so a driver that read only its constructor options would turn every MTConnect config
-///         edit into a silent no-op that still seals the deployment green. This class therefore
+///         <b>The <c>driverConfigJson</c> argument is honoured, not decorative.</b> <see cref="IDriver.InitializeAsync"/>
+///         and <see cref="ReinitializeAsync"/> both take the document, and the contract is that the driver
+///         serves it — a driver that read only its constructor options would turn an in-place config
+///         change into a silent no-op. (The runtime itself now applies a config change by respawning,
+///         #516/#665.) This class therefore
 ///         re-parses the document (<see cref="ParseOptions"/>) whenever it carries a real body,
 ///         matching S7/AbCip/TwinCAT/Galaxy rather than the Modbus/FOCAS/OpcUaClient drivers that
 ///         ignore the argument. A blank / <c>{}</c> / <c>[]</c> document means "no config supplied"

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus/ModbusDriver.cs

@@ -95,7 +95,7 @@ public sealed class ModbusDriver
     ///     concurrent operations would dispose each other's freshly-built transport or null
     ///     <c>_transport</c> out from under an in-flight connect. Not hypothetical:
     ///     <c>DriverInstanceActor</c> dispatches initialize on a fire-and-forget <c>Task.Run</c> and
-    ///     its <c>AdoptConfigDuringInit</c> can fire twice back to back. Same shape as
+    ///     a reconnect retry tick can start a second attempt while the first is still running. Same shape as
     ///     <c>MqttDriver._lifecycleGate</c>.
     /// </summary>
     private readonly SemaphoreSlim _lifecycleGate = new(1, 1);
@@ -297,9 +297,9 @@ public sealed class ModbusDriver
             // Release whatever a PREVIOUS initialize published before building the replacements. All
             // three fields assigned below (_transport, _probeCts, _reprobeCts) were simply overwritten,
             // so a second initialize on a live driver stranded a connected transport plus two running
-            // background loops that no later dispose could reach. Reachable without any teardown of
-            // ours: DriverInstanceActor re-runs InitializeAsync with no ShutdownAsync when an ApplyDelta
-            // lands while the driver is in Connecting/Reconnecting (AdoptConfigDuringInit).
+            // background loops that no later dispose could reach. The IDriver contract lets a
+            // caller re-initialise a live driver without ShutdownAsync, and DriverInstanceActor's retry tick
+            // can overlap a still-running attempt, so this must not rely on a teardown having happened.
             // Deliberately NOT the shared TeardownAsync(): that also disposes _poll, which tears down
             // every ACTIVE SUBSCRIPTION — and nothing re-subscribes them afterwards, because a
             // mid-life re-initialize is not a shutdown the OPC UA layer knows to re-drive. A caller

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt/MqttDriver.cs

@@ -983,9 +983,9 @@ public sealed class MqttDriver
             // published below (_connection, _primaryHost) are IAsyncDisposable and were previously
             // overwritten, so a second initialize on a live driver stranded a connected, supervised
             // broker session — plus a whole second primary-host connection — that no later dispose
-            // could reach. Reachable without any teardown of ours: DriverInstanceActor re-runs
-            // InitializeAsync with no ShutdownAsync when an ApplyDelta lands while the driver is in
-            // Connecting/Reconnecting (AdoptConfigDuringInit). Idempotent, so the ReinitializeAsync
+            // could reach. The IDriver contract lets a caller
+            // re-initialise a live driver without ShutdownAsync, and a reconnect retry can overlap a running
+            // attempt. Idempotent, so the ReinitializeAsync
             // rebuild branch calling TeardownAsync first costs a no-op, and a first initialize sees
             // three nulls.
             await TeardownAsync().ConfigureAwait(false);

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient/OpcUaClientDriver.cs

@@ -227,8 +227,8 @@ public sealed class OpcUaClientDriver : IDriver, ITagDiscovery, IReadable, IWrit
     /// <inheritdoc />
     public async Task InitializeAsync(string driverConfigJson, CancellationToken cancellationToken)
     {
-        // #630: InitializeAsync is reachable on a live driver (DriverInstanceActor.AdoptConfigDuringInit runs
-        // it with no teardown first); `Session = session` below would otherwise orphan the previous session,
+        // #630: InitializeAsync is reachable on a live driver with no teardown first (the IDriver contract
+        // allows it, and a reconnect retry can overlap a running attempt); `Session = session` below would otherwise orphan the previous session,
         // its keep-alive handler and any reconnect handler.
         await ReleaseSessionAsync(cancellationToken).ConfigureAwait(false);
         _health = new DriverHealth(DriverState.Initializing, null, null);

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7/S7Driver.cs

@@ -225,8 +225,8 @@ public sealed class S7Driver
     /// <inheritdoc />
     public async Task InitializeAsync(string driverConfigJson, CancellationToken cancellationToken)
     {
-        // #630: InitializeAsync is reachable on a live driver (DriverInstanceActor.AdoptConfigDuringInit
-        // runs it with no teardown first). Stop the previous probe loop and drop the previous connection
+        // #630: InitializeAsync is reachable on a live driver with no teardown first (the IDriver contract
+        // allows it, and a reconnect retry can overlap a running attempt). Stop the previous probe loop and drop the previous connection
         // before they are overwritten below. Deliberately NOT ShutdownAsync: that also drops _poll and the
         // subscriptions, which are owned by the shutdown path (the actor re-subscribes after every successful init).
         await ReleaseConnectionAsync().ConfigureAwait(false);

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT/TwinCATDriver.cs

@@ -113,8 +113,8 @@ public sealed class TwinCATDriver : IDriver, IReadable, IWritable, ITagDiscovery
     /// <inheritdoc />
     public async Task InitializeAsync(string driverConfigJson, CancellationToken cancellationToken)
     {
-        // #630: InitializeAsync is reachable on a live driver (DriverInstanceActor.AdoptConfigDuringInit
-        // runs it with no teardown first). Release the previous device states' probe loops + clients before
+        // #630: InitializeAsync is reachable on a live driver with no teardown first (the IDriver contract
+        // allows it, and a reconnect retry can overlap a running attempt). Release the previous device states' probe loops + clients before
         // the overwrite below. Deliberately NOT ShutdownAsync: that also drops _poll and the subscriptions.
         await ReleaseDeviceStatesAsync().ConfigureAwait(false);
         _health = new DriverHealth(DriverState.Initializing, null, null);

src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Drivers/DeploymentArtifact.cs

@@ -406,7 +406,7 @@ internal sealed class ParsedDeploymentArtifact : IDisposable
         // v3: each spec's DriverConfig is the MERGED config the driver factory binds from —
         // DriverConfig (protocol/channel) + per-Device DeviceConfig (endpoint) + the driver's authored
         // raw tags (RawTags array, keyed by RawPath) — folded once here via DriverDeviceConfigMerger so
-        // both spawn (TryCreate) and redeploy (ApplyDelta) hand the driver the same shape.
+        // the factory (TryCreate) and the init (InitializeRequested) hand the driver the same shape.
         var rawTagsByDriver = BuildRawTagsByDriver(root);
         var deviceRowsByDriver = BuildDeviceRowsByDriver(root);
 

src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Drivers/DriverHostActor.cs

@@ -391,10 +391,6 @@ public sealed class DriverHostActor : ReceiveActor, IWithTimers, IWithUnboundedS
     /// value maps so stale condition state never leaks across redeploys.</summary>
     private readonly NativeAlarmProjector _nativeAlarmProjector = new();
 
-    /// <summary>In-flight <see cref="DriverInstanceActor.ApplyDelta"/> sends, keyed by correlation, so
-    /// <see cref="HandleApplyResult"/> can advance the cached spec only once the child confirms it adopted
-    /// the config (#516). Bounded by the number of driver children with a delta in flight.</summary>
-    private readonly Dictionary<CorrelationId, DriverInstanceSpec> _pendingDelta = new();
 
     /// <summary>One driver child's desired subscription payload — exactly the
     /// <see cref="DriverInstanceActor.SetDesiredSubscriptions"/> the apply's bulk push sent it.</summary>
@@ -1345,8 +1341,6 @@ public sealed class DriverHostActor : ReceiveActor, IWithTimers, IWithUnboundedS
         Receive<DriverInstanceActor.AttributeAlarmPublished>(ForwardNativeAlarm);
         Receive<DriverInstanceActor.ConnectivityChanged>(OnDriverConnectivityChanged);
         Receive<CommsRecoveryAudit>(HandleCommsRecoveryAudit);
-        Receive<DriverInstanceActor.DeltaApplied>(HandleDeltaApplied);
-        Receive<DriverInstanceActor.ApplyResult>(HandleApplyResult);
         Receive<RestartDriver>(HandleRestartDriver);
         Receive<DriverInstanceActor.ReprovisionRequested>(HandleReprovisionRequested);
         Receive<ReprovisionDeferred>(m => ReprovisionChild(m.Request, m.Child));
@@ -1408,8 +1402,6 @@ public sealed class DriverHostActor : ReceiveActor, IWithTimers, IWithUnboundedS
         Receive<DriverInstanceActor.AttributeAlarmPublished>(ForwardNativeAlarm);
         Receive<DriverInstanceActor.ConnectivityChanged>(OnDriverConnectivityChanged);
         Receive<CommsRecoveryAudit>(HandleCommsRecoveryAudit);
-        Receive<DriverInstanceActor.DeltaApplied>(HandleDeltaApplied);
-        Receive<DriverInstanceActor.ApplyResult>(HandleApplyResult);
         Receive<RestartDriver>(HandleRestartDriver);
         Receive<DriverInstanceActor.ReprovisionRequested>(HandleReprovisionRequested);
         Receive<ReprovisionDeferred>(m => ReprovisionChild(m.Request, m.Child));
@@ -2284,10 +2276,6 @@ public sealed class DriverHostActor : ReceiveActor, IWithTimers, IWithUnboundedS
         // Likewise the 03/S15 recovery audit: a timer armed before the host went Stale has nothing to report
         // on (no latch was set while Stale, and the rebuild re-establishes every node's status anyway).
         Receive<CommsRecoveryAudit>(_ => { });
-        // A late DeltaApplied (an apply completed just before the DB went Stale) — re-register the driver's
-        // mux adapter anyway; it simply re-reads the driver's current refs (harmless, no DB access).
-        Receive<DriverInstanceActor.DeltaApplied>(HandleDeltaApplied);
-        Receive<DriverInstanceActor.ApplyResult>(HandleApplyResult);
         Receive<SubscribeAck>(_ => { /* PubSub ack */ });
         Timers.StartPeriodicTimer("retry-db", RetryConfigDbConnection.Instance, ReconnectInterval);
     }
@@ -2704,7 +2692,7 @@ public sealed class DriverHostActor : ReceiveActor, IWithTimers, IWithUnboundedS
 
     /// <summary>
     ///     Read the deployment artifact + reconcile the set of running <see cref="DriverInstanceActor"/>
-    ///     children. Spawn missing, ApplyDelta on config change, stop removed/disabled drivers.
+    ///     children. Spawn missing, respawn on config change, stop removed/disabled drivers.
     ///     When the artifact blob is empty (legacy ControlPlane tests, smoke fixtures) the reconcile is
     ///     SKIPPED outright — see the issue #485 guard below — and when the configured
     ///     <see cref="IDriverFactory"/> can't materialise any of the requested types this is a no-op.
@@ -2917,16 +2905,11 @@ public sealed class DriverHostActor : ReceiveActor, IWithTimers, IWithUnboundedS
         var plan = DriverSpawnPlanner.Compute(snapshots, specs);
 
         foreach (var id in plan.ToStop) StopChild(id);
-        foreach (var spec in plan.ToApplyDelta) ApplyChildDelta(spec);
         foreach (var spec in plan.ToSpawn) SpawnChild(spec);
 
         // v3 (WP7): a dependency-consumer driver's declared dependency refs change when its tags/scripts are
-        // edited — the adapter must re-register the NEW set on the mux. Newly-spawned adapters register in
-        // PreStart; an ApplyDelta'd driver's adapter is re-registered when the child reports it finished
-        // reinitialising (DriverInstanceActor.DeltaApplied → HandleDeltaApplied). That notification is
-        // sequenced AFTER ReinitializeAsync rebuilds DependencyRefs — a synchronous re-register HERE would
-        // re-read the STALE ref set (ApplyDelta runs asynchronously on the child), so it is deliberately NOT
-        // done inline.
+        // edited. That edit changes its DriverConfig, which respawns it (#516), and the respawned driver's
+        // adapter registers the NEW set in PreStart — no separate re-register is needed (#665).
     }
 
     /// <summary>
@@ -3557,69 +3540,6 @@ public sealed class DriverHostActor : ReceiveActor, IWithTimers, IWithUnboundedS
             Context.Stop(adapter);
     }
 
-    /// <summary>
-    ///     Sends an in-place config delta to a running child.
-    ///     <para><b>Unreachable from the reconcile path since #516</b> — a DriverConfig change is now a
-    ///     stop + respawn (<see cref="DriverSpawnPlanner"/>), so <c>ToApplyDelta</c> is always empty.
-    ///     Kept because the seam is still exercised by <c>DriverInstanceActor</c>'s own mid-connect config
-    ///     adoption.</para>
-    ///     <para><b>Two seals were removed here.</b> This used to overwrite the cached
-    ///     <c>Spec</c> SYNCHRONOUSLY, before the child had even dequeued the message — so the host
-    ///     immediately believed the new config was live, the NEXT reconcile computed no delta against it,
-    ///     and any drift was sealed permanently. It also <c>Tell</c>d with no <c>Receive&lt;ApplyResult&gt;</c>
-    ///     handler registered, so a FAILED reinit — including Galaxy's deliberate
-    ///     <c>NotSupportedException</c> — dead-lettered and was never surfaced.</para>
-    /// </summary>
-    private void ApplyChildDelta(DriverInstanceSpec spec)
-    {
-        if (!_children.TryGetValue(spec.DriverInstanceId, out var entry)) return;
-        var correlation = CorrelationId.NewId();
-        _pendingDelta[correlation] = spec;
-        entry.Actor.Tell(new DriverInstanceActor.ApplyDelta(spec.DriverConfig, correlation), Self);
-        _log.Debug("DriverHost {Node}: ApplyDelta queued for {Id}", _localNode, spec.DriverInstanceId);
-    }
-
-    /// <summary>
-    ///     A child's reply to <see cref="ApplyChildDelta"/>. On success the cached <c>Spec</c> is advanced —
-    ///     only now, when the child has actually adopted the config, so a failed reinit leaves the host
-    ///     believing the OLD config is live and the next reconcile re-attempts the change instead of
-    ///     silently treating the drift as applied. A failure is logged at Error rather than swallowed.
-    /// </summary>
-    private void HandleApplyResult(DriverInstanceActor.ApplyResult msg)
-    {
-        if (msg.Success)
-        {
-            if (_pendingDelta.Remove(msg.Correlation, out var spec)
-                && _children.TryGetValue(spec.DriverInstanceId, out var entry))
-            {
-                // A delta can change Name, Enabled, ClusterId etc. alongside the config.
-                _children[spec.DriverInstanceId] = entry with { Spec = spec };
-            }
-            return;
-        }
-
-        _pendingDelta.Remove(msg.Correlation, out var failed);
-        _log.Error(
-            "DriverHost {Node}: driver {Id} REJECTED an in-place config change ({Reason}) — the host keeps " +
-            "the previous config so the next reconcile re-attempts it",
-            _localNode, failed?.DriverInstanceId ?? "<unknown>", msg.Reason ?? "no reason given");
-    }
-
-    /// <summary>
-    ///     A driver child finished applying an in-place <see cref="DriverInstanceActor.ApplyDelta"/> (its
-    ///     <see cref="IDriver.ReinitializeAsync"/> completed). Re-register THAT driver's dependency-consumer
-    ///     mux adapter so a changed dependency-ref set (calc tags/scripts edited during the redeploy) is
-    ///     adopted on the mux. This runs AFTER reinit — closing the ordering hazard where a synchronous
-    ///     re-register at ApplyDelta dispatch would re-read the driver's stale
-    ///     <see cref="IDependencyConsumer.DependencyRefs"/>. A Tell (no blocking); a no-op for a driver with no
-    ///     adapter (not an <see cref="IDependencyConsumer"/>, or no mux wired on this node).
-    /// </summary>
-    private void HandleDeltaApplied(DriverInstanceActor.DeltaApplied msg)
-    {
-        if (_depConsumerAdapters.TryGetValue(msg.DriverInstanceId, out var adapter))
-            adapter.Tell(new ZB.MOM.WW.OtOpcUa.Runtime.VirtualTags.DependencyConsumerMuxAdapter.ReRegister());
-    }
-
     private void StopChild(string driverInstanceId)
     {
         if (!_children.TryGetValue(driverInstanceId, out var entry)) return;

src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Drivers/DriverInstanceActor.cs

@@ -25,8 +25,7 @@ file sealed class HealthPollTick
 ///   <item><c>Failed</c> — terminal until parent restarts the actor.</item>
 /// </list>
 ///
-/// Engine wiring (subscriptions → AttributeValueUpdate publishes, ApplyDelta-driven Reinitialize,
-/// per-tag write Asks) is staged for follow-up F7. This skeleton compiles + has a working
+/// Engine wiring (subscriptions → AttributeValueUpdate publishes, per-tag write Asks) is staged for follow-up F7. This skeleton compiles + has a working
 /// state machine so the Phase 6 control-plane integration tests can target it.
 /// </summary>
 public sealed class DriverInstanceActor : ReceiveActor, IWithTimers
@@ -41,7 +40,7 @@ public sealed class DriverInstanceActor : ReceiveActor, IWithTimers
     /// <c>Connected=true</c> on entering the Connected state, <c>false</c> on entering Reconnecting. The host
     /// annotates this driver's native alarm conditions' source-data Quality from it (comms lost → Bad,
     /// restored → Good) — independently of alarm transitions, since a comms-lost driver emits no alarm
-    /// events. Fire-and-forget, mirroring <see cref="DeltaApplied"/>.</summary>
+    /// events. Fire-and-forget.</summary>
     public sealed record ConnectivityChanged(string DriverInstanceId, bool Connected);
 
     /// <summary>
@@ -62,18 +61,6 @@ public sealed class DriverInstanceActor : ReceiveActor, IWithTimers
     /// <param name="DriverInstanceId">The driver instance that was restarted.</param>
     /// <param name="Reason">The type name of the exception that tripped supervision, for the host's log.</param>
     public sealed record ReprovisionRequested(string DriverInstanceId, string Reason);
-    public sealed record ApplyDelta(string DriverConfigJson, CorrelationId Correlation);
-    public sealed record ApplyResult(bool Success, string? Reason, CorrelationId Correlation);
-    /// <summary>
-    ///     Sent to the parent (<see cref="DriverHostActor"/>) AFTER an <see cref="ApplyDelta"/> has fully
-    ///     re-initialised the driver (i.e. <see cref="IDriver.ReinitializeAsync"/> completed). The host uses
-    ///     it to re-register this driver's dependency-consumer mux adapter: a driver may rebuild its declared
-    ///     <see cref="IDependencyConsumer.DependencyRefs"/> during reinit (the Calculation driver re-binds its
-    ///     calc tags), so the re-register MUST happen after reinit — NOT synchronously alongside the ApplyDelta
-    ///     dispatch, which would re-read the STALE ref set. Emitted only on a successful apply.
-    /// </summary>
-    /// <param name="DriverInstanceId">The instance whose adapter should be re-registered.</param>
-    public sealed record DeltaApplied(string DriverInstanceId);
     public sealed record WriteAttribute(string TagId, object Value);
     public sealed record WriteAttributeResult(bool Success, string? Reason);
     /// <summary>
@@ -221,15 +208,9 @@ public sealed class DriverInstanceActor : ReceiveActor, IWithTimers
     private readonly ILoggingAdapter _log = Context.GetLogger();
     private string? _currentConfigJson;
 
-    /// <summary>#664: set when <see cref="AdoptConfigDuringInit"/> adopts a new config mid-connect; the next
-    /// (generation-matched) <see cref="InitializeSucceeded"/> sends <see cref="DeltaApplied"/> to the parent and
-    /// clears it, so a dependency consumer's mux interest is re-registered against the ADOPTED config — the
-    /// same post-reinit notification the Connected <see cref="HandleApplyDeltaAsync"/> path sends.</summary>
-    private bool _adoptedConfigPendingNotify;
-
     /// <summary>Monotonic token tagging each <see cref="InitializeAsync"/> attempt. An init result is
     /// honoured only when its generation matches the latest; an older result is from a superseded attempt
-    /// (e.g. an <see cref="ApplyDelta"/> adopted a new config mid-(re)connect) and is dropped. Touched only
+    /// (a retry tick that overlapped a still-running attempt) and is dropped. Touched only
     /// on the actor thread, so no lock is needed.</summary>
     private int _initGeneration;
 
@@ -442,7 +423,6 @@ public sealed class DriverInstanceActor : ReceiveActor, IWithTimers
         // Stubbed drivers accept the standard message contracts but return deterministic
         // success without touching real hardware. Read returns null; Write succeeds.
         Receive<InitializeRequested>(_ => { /* no-op */ });
-        Receive<ApplyDelta>(msg => Sender.Tell(new ApplyResult(true, "stubbed", msg.Correlation)));
         Receive<WriteAttribute>(_ => Sender.Tell(new WriteAttributeResult(true, "stubbed")));
         // Stubbed drivers have no upstream alarm system — swallow the ack (it's fire-and-forget, no reply).
         Receive<RouteAlarmAck>(_ => { /* stubbed drivers have no alarm backend */ });
@@ -468,13 +448,11 @@ public sealed class DriverInstanceActor : ReceiveActor, IWithTimers
         // fire-and-forget — no reply to surface — and the OPC UA condition state already committed locally).
         Receive<RouteAlarmAck>(_ =>
             _log.Debug("DriverInstance {Id}: alarm ack arrived during connect — dropped (driver not connected)", _driverInstanceId));
-        Receive<ApplyDelta>(AdoptConfigDuringInit);
         Receive<InitializeSucceeded>(msg =>
         {
             if (msg.Generation != _initGeneration) return;
             _log.Info("DriverInstance {Id}: connected", _driverInstanceId);
             Become(Connected);
-            NotifyAdoptedConfig();
             PublishHealthSnapshot();
             ResubscribeDesired();
             AttachAlarmSource();
@@ -522,7 +500,6 @@ public sealed class DriverInstanceActor : ReceiveActor, IWithTimers
         // reconnects but never manages a read is measured from THIS connect, not from a stale earlier one.
         _connectedSinceUtc = DateTime.UtcNow;
 
-        ReceiveAsync<ApplyDelta>(HandleApplyDeltaAsync);
         Receive<DisconnectObserved>(msg =>
         {
             _log.Warning("DriverInstance {Id}: disconnect observed ({Reason}); reconnecting",
@@ -771,14 +748,12 @@ public sealed class DriverInstanceActor : ReceiveActor, IWithTimers
         // no reply — the OPC UA condition state already committed locally on the Part 9 ack).
         Receive<RouteAlarmAck>(_ =>
             _log.Debug("DriverInstance {Id}: alarm ack arrived during reconnect — dropped (driver not connected)", _driverInstanceId));
-        Receive<ApplyDelta>(AdoptConfigDuringInit);
         Receive<InitializeSucceeded>(msg =>
         {
             if (msg.Generation != _initGeneration) return;
             Timers.Cancel("retry-connect");
             _log.Info("DriverInstance {Id}: reconnected", _driverInstanceId);
             Become(Connected);
-            NotifyAdoptedConfig();
             PublishHealthSnapshot();
             ResubscribeDesired();
             AttachAlarmSource();
@@ -875,94 +850,6 @@ public sealed class DriverInstanceActor : ReceiveActor, IWithTimers
         });
     }
 
-    /// <summary>Adopt a new config while not connected: ApplyDelta in Connecting/Reconnecting re-inits
-    /// immediately with the new config. <see cref="InitializeAsync"/> swaps <c>_currentConfigJson</c> and
-    /// bumps the generation, so the in-flight (old-config) init is superseded and its result is dropped.
-    /// The actor stays in its current state; the new init's result drives the next transition. In
-    /// Reconnecting the retry timer is left running — if this immediate attempt fails it keeps retrying
-    /// the new config (a redundant concurrent attempt is deduped by the generation guard).</summary>
-    private void AdoptConfigDuringInit(ApplyDelta msg)
-    {
-        _log.Info("DriverInstance {Id}: ApplyDelta during (re)connect — adopting new config, re-initialising now",
-            _driverInstanceId);
-        InitializeAsync(msg.DriverConfigJson);
-        _adoptedConfigPendingNotify = true;
-        Sender.Tell(new ApplyResult(true, "config adopted; reinitializing", msg.Correlation));
-    }
-
-    /// <summary>Send the deferred <see cref="DeltaApplied"/> for a mid-connect adoption (#664) once the driver
-    /// has actually initialised on the adopted config. A no-op otherwise.</summary>
-    private void NotifyAdoptedConfig()
-    {
-        if (!_adoptedConfigPendingNotify) return;
-        _adoptedConfigPendingNotify = false;
-        Context.Parent.Tell(new DeltaApplied(_driverInstanceId));
-    }
-
-    /// <summary>Adopt a new config while Connected, in place, via <see cref="IDriver.ReinitializeAsync"/>.
-    /// <para>#663: every driver's reinit releases its device/session state (#630), so the driver-side data and
-    /// native-alarm subscriptions do not survive it — but this handler used to keep both handles, and the
-    /// health-poll reconcile only re-subscribes a MISSING handle, so the driver went silent until a
-    /// reconnect or respawn. Both subscriptions are now released explicitly BEFORE the reinit (explicitly,
-    /// not just by nulling the handles, so a driver whose reinit keeps its subscriptions is not left
-    /// holding two) and re-established after it — in a <c>finally</c>, because a failed reinit has already
-    /// lost them too. Reinit stays the adoption path rather than shutdown + initialise: Calculation and
-    /// Galaxy take their config at construction and ignore <see cref="IDriver.InitializeAsync"/>'s JSON.</para>
-    /// <para>Not reachable from a deploy since #516 (a DriverConfig change respawns the driver).</para></summary>
-    private async Task HandleApplyDeltaAsync(ApplyDelta msg)
-    {
-        var replyTo = Sender;
-        await UnsubscribeAsync();
-        await ReleaseAlarmSubscriptionAsync();
-        try
-        {
-            await _driver.ReinitializeAsync(msg.DriverConfigJson, CancellationToken.None);
-            _currentConfigJson = msg.DriverConfigJson;
-            // The driver may have rebuilt its dependency-consumer interest during reinit (the Calculation
-            // driver re-binds its calc tags + dependency refs). Notify the parent so it re-registers this
-            // driver's mux adapter AFTER reinit completed — a synchronous re-register at ApplyDelta-dispatch
-            // time would re-read the driver's STALE DependencyRefs. Parent Tell (fire-and-forget); the
-            // continuation resumes on the actor context (no ConfigureAwait) so Context.Parent is live.
-            Context.Parent.Tell(new DeltaApplied(_driverInstanceId));
-            replyTo.Tell(new ApplyResult(true, null, msg.Correlation));
-        }
-        catch (Exception ex)
-        {
-            replyTo.Tell(new ApplyResult(false, ex.Message, msg.Correlation));
-        }
-        finally
-        {
-            ResubscribeDesired();
-            AttachAlarmSource();
-            SubscribeDesiredAlarms();
-        }
-    }
-
-    /// <summary>Release the native-alarm subscription at the driver (best-effort, bounded) and drop the
-    /// actor's handler + handle. The in-place reinit counterpart of the data <see cref="UnsubscribeAsync"/>
-    /// (#663).</summary>
-    private async Task ReleaseAlarmSubscriptionAsync()
-    {
-        if (_driver is IAlarmSource src && _alarmSubscriptionHandle is { } handle)
-        {
-            try
-            {
-                using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
-                await _invoker.ExecuteAsync(
-                    DriverCapability.AlarmSubscribe,
-                    _driverInstanceId,
-                    async ct => await src.UnsubscribeAlarmsAsync(handle, ct),
-                    cts.Token);
-            }
-            catch (Exception ex)
-            {
-                _log.Warning(ex, "DriverInstance {Id}: releasing the native-alarm subscription ({Diag}) threw (continuing)",
-                    _driverInstanceId, handle.DiagnosticId);
-            }
-        }
-        DetachAlarmSource();
-    }
-
     private async Task HandleWriteAsync(WriteAttribute msg)
     {
         var replyTo = Sender;

src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Drivers/DriverSpawnPlan.cs

@@ -3,38 +3,31 @@ namespace ZB.MOM.WW.OtOpcUa.Runtime.Drivers;
 /// <summary>
 ///     Pure diff between the currently-running driver children (keyed by
 ///     <c>DriverInstance.DriverInstanceId</c>) and the target spec list from a freshly-applied
-///     deployment artifact. The DriverHostActor consumes the three lists and calls
-///     spawn / ApplyDelta / stop on its child actors accordingly.
+///     deployment artifact. The DriverHostActor consumes the two lists and calls
+///     spawn / stop on its child actors accordingly. There is no in-place config path: since #516 a config
+///     change is a stop + respawn, and #665 deleted the unreachable in-place <c>ApplyDelta</c> seam.
 /// </summary>
-/// <param name="ToSpawn">Specs with no current child — create a new actor.</param>
-/// <param name="ToApplyDelta">
-///     In-place config deltas. <b>Always empty since #516</b> — a DriverConfig change is now a
-///     stop + respawn so the factory is the single parse authority. Retained because
-///     <c>DriverInstanceActor</c> still handles <c>ApplyDelta</c> on its own config-adoption path
-///     (a config arriving mid-connect), and removing the list would hide that seam.
-/// </param>
+/// <param name="ToSpawn">Specs with no current child (or whose child is being replaced) — create a new actor.</param>
 /// <param name="ToStop">DriverInstanceIds currently running but missing from the new artifact, or now disabled.</param>
 public sealed record DriverSpawnPlan(
     IReadOnlyList<DriverInstanceSpec> ToSpawn,
-    IReadOnlyList<DriverInstanceSpec> ToApplyDelta,
     IReadOnlyList<string> ToStop);
 
 public static class DriverSpawnPlanner
 {
     /// <summary>
-    ///     Compute the spawn/delta/stop sets. Disabled entries in <paramref name="target"/> are
+    ///     Compute the spawn/stop sets. Disabled entries in <paramref name="target"/> are
     ///     treated as "not desired here": if a child exists for the id it goes into ToStop,
     ///     otherwise the row is dropped entirely (no spawn for a disabled driver).
     /// </summary>
     /// <param name="current">The currently running driver children keyed by ID.</param>
     /// <param name="target">The target driver instances from the deployment artifact.</param>
-    /// <returns>The computed <see cref="DriverSpawnPlan"/> with spawn, apply-delta, and stop sets.</returns>
+    /// <returns>The computed <see cref="DriverSpawnPlan"/> with spawn and stop sets.</returns>
     public static DriverSpawnPlan Compute(
         IReadOnlyDictionary<string, DriverChildSnapshot> current,
         IReadOnlyList<DriverInstanceSpec> target)
     {
         var toSpawn = new List<DriverInstanceSpec>();
-        var toDelta = new List<DriverInstanceSpec>();
         var toStop = new List<string>();
 
         var targetById = new Dictionary<string, DriverInstanceSpec>(StringComparer.Ordinal);
@@ -83,7 +76,7 @@ public static class DriverSpawnPlanner
             toSpawn.Add(spec);
         }
 
-        return new DriverSpawnPlan(toSpawn, toDelta, toStop);
+        return new DriverSpawnPlan(toSpawn, toStop);
     }
 }
 

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/AbLegacyReinitializeReleasesStateTests.cs

@@ -5,8 +5,8 @@ using ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.PlcFamilies;
 namespace ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests;
 
 /// <summary>
-///     #630 — <c>InitializeAsync</c> on a live driver (<c>DriverInstanceActor.AdoptConfigDuringInit</c> runs
-///     it with no teardown first) overwrote <c>_devices[host]</c> and orphaned the previous state's
+///     #630 — <c>InitializeAsync</c> on a live driver with no teardown first (the <c>IDriver</c> contract
+///     allows it) overwrote <c>_devices[host]</c> and orphaned the previous state's
 ///     probe loop + runtime. It now releases them first.
 /// </summary>
 [Trait("Category", "Unit")]

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

@@ -396,7 +396,7 @@ public sealed class CalculationDriverTests
     }
 
     /// <summary>The skip ledger must be REBUILT on ReinitializeAsync, not just at construction — an
-    /// ApplyDelta that drops a tag's scriptId (or adds a new tag with none) must be reflected immediately,
+    /// in-place config change that drops a tag's scriptId (or adds a new tag with none) must be reflected immediately,
     /// since RebuildTagTable is the one routine both the ctor and reinit share.</summary>
     [Fact]
     public async Task GetSkippedTags_updates_after_reinitialize()
@@ -414,9 +414,9 @@ public sealed class CalculationDriverTests
     }
 
     /// <summary>
-    ///     Gitea #664 — <c>InitializeAsync</c> re-runs on a LIVE driver with a new config when an ApplyDelta lands
-    ///     mid-connect (<c>DriverInstanceActor.AdoptConfigDuringInit</c>). It used to ignore the JSON, so the
-    ///     driver kept its constructor tag set while the deploy reported the change applied. A config with a body
+    ///     Gitea #664 — <c>InitializeAsync</c> must serve the config document it is handed (the <c>IDriver</c>
+    ///     contract). It used to ignore the JSON, so a live driver re-initialised with a new config kept its
+    ///     constructor tag set. A config with a body
     ///     now rebuilds the tag table (and the dependency-ref set the host re-registers from).
     /// </summary>
     [Fact]

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/FocasReinitializeReleasesStateTests.cs

@@ -5,8 +5,8 @@ using ZB.MOM.WW.OtOpcUa.Driver.FOCAS;
 namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests;
 
 /// <summary>
-///     #630 — <c>InitializeAsync</c> on a live driver (<c>DriverInstanceActor.AdoptConfigDuringInit</c> runs
-///     it with no teardown first) overwrote <c>_devices[host]</c> and orphaned the previous state's
+///     #630 — <c>InitializeAsync</c> on a live driver with no teardown first (the <c>IDriver</c> contract
+///     allows it) overwrote <c>_devices[host]</c> and orphaned the previous state's
 ///     probe loop + client. It now releases them first.
 /// </summary>
 [Trait("Category", "Unit")]

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Tests/GalaxyDriverFactoryTests.cs

@@ -209,9 +209,8 @@ public sealed class GalaxyDriverFactoryTests
     }
 
     /// <summary>
-    ///     Gitea #664 — <c>InitializeAsync</c> re-runs on a live driver with a NEW config when an ApplyDelta lands
-    ///     mid-connect. Galaxy cannot hot-swap its options, and it used to ignore the JSON — connecting on the OLD
-    ///     endpoint while the deploy reported the change applied. A non-equivalent config is now refused, exactly
+    ///     Gitea #664 — <c>InitializeAsync</c> must not silently ignore the config it is handed. Galaxy cannot
+    ///     hot-swap its options, and it used to ignore the JSON — connecting on the OLD endpoint. A non-equivalent config is now refused, exactly
     ///     as <c>ReinitializeAsync</c> refuses it; an equivalent one still initialises.
     /// </summary>
     [Fact]

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Tests/MTConnectDriverLifecycleTests.cs

@@ -265,9 +265,8 @@ public sealed class MTConnectDriverLifecycleTests
     [Fact]
     public async Task Initialize_honours_the_config_json_over_the_constructor_options()
     {
-        // The runtime delivers a config change ONLY through this argument (DriverInstanceActor
-        // ApplyDelta -> ReinitializeAsync(json) on the LIVE instance). Ignoring it would make every
-        // MTConnect config change a silent no-op that still seals the deployment green.
+        // The IDriver contract: the driver serves the config document it is handed, not only its
+        // constructor options — ignoring it would turn an in-place config change into a silent no-op.
         MTConnectDriverOptions? seen = null;
         var driver = new MTConnectDriver(Opts(), "mt1", o =>
         {
@@ -533,7 +532,7 @@ public sealed class MTConnectDriverLifecycleTests
     [Fact]
     public async Task Reinitialize_with_an_unreadable_config_keeps_the_running_driver_serving()
     {
-        // Blast radius: an unparseable config edit fails the DEPLOYMENT (ApplyResult(false)); it must
+        // Blast radius: an unparseable in-place config edit fails the reinitialize call; it must
         // not down a driver that is happily serving its previous, valid configuration.
         var (driver, client) = await InitializedDriverAsync();
 

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests/ModbusLifecycleHygieneTests.cs

@@ -225,9 +225,8 @@ public sealed class ModbusLifecycleHygieneTests
     // -------------------- Re-initialize transport hygiene --------------------
 
     /// <summary>
-    ///     A second <c>InitializeAsync</c> on a live driver — the shape
-    ///     <c>DriverInstanceActor.AdoptConfigDuringInit</c> produces when an ApplyDelta lands while the
-    ///     driver is Connecting/Reconnecting — must dispose the transport the previous initialize
+    ///     A second <c>InitializeAsync</c> on a live driver with no teardown between (the <c>IDriver</c>
+    ///     contract allows it) must dispose the transport the previous initialize
     ///     published before publishing a new one. Pre-fix <c>_transport</c> was simply overwritten,
     ///     stranding a connected transport no later dispose could reach.
     /// </summary>
@@ -251,7 +250,7 @@ public sealed class ModbusLifecycleHygieneTests
         });
 
         await drv.InitializeAsync("{}", CancellationToken.None);
-        // No ShutdownAsync in between — exactly what AdoptConfigDuringInit does.
+        // No ShutdownAsync in between.
         await drv.InitializeAsync("{}", CancellationToken.None);
 
         handed.Count.ShouldBe(2, "each initialize must build its own transport");
@@ -415,8 +414,8 @@ public sealed class ModbusLifecycleHygieneTests
 
     /// <summary>
     ///     Two initializes racing on the same driver — the shape <c>DriverInstanceActor</c> produces by
-    ///     dispatching initialize on a fire-and-forget <c>Task.Run</c> with <c>AdoptConfigDuringInit</c>
-    ///     firing twice — must serialize on the lifecycle gate. Ungated, the teardown at the top of one
+    ///     dispatching initialize on a fire-and-forget <c>Task.Run</c>, where a reconnect retry tick can
+    ///     overlap a still-running attempt — must serialize on the lifecycle gate. Ungated, the teardown at the top of one
     ///     initialize disposes the transport the other just published (or nulls <c>_transport</c>
     ///     mid-connect), leaving the driver holding a disposed transport.
     /// </summary>

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt.Tests/MqttDriverSessionLifecycleTests.cs

@@ -28,10 +28,9 @@ public sealed class MqttDriverSessionLifecycleTests
     /// </summary>
     /// <remarks>
     ///     <para>
-    ///         Reachable with no teardown of the driver's own: <c>DriverInstanceActor</c> re-runs
-    ///         <c>InitializeAsync</c> with no <c>ShutdownAsync</c> when an <c>ApplyDelta</c> arrives while
-    ///         the driver is Connecting/Reconnecting (<c>AdoptConfigDuringInit</c>). The
-    ///         <c>teardownFirst</c> flag on the #527 retry path covers only the retry path.
+    ///         The <c>IDriver</c> contract allows re-initialising a live driver with no
+    ///         <c>ShutdownAsync</c>, and the #527 retry path's <c>teardownFirst</c> flag does not stop a
+    ///         retry overlapping a still-running attempt, so the driver must not rely on a teardown.
     ///     </para>
     ///     <para>
     ///         The assertion is the broker's <b>live socket count</b>, not the driver's own view: a leak

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7.Tests/S7DriverReconnectTests.cs

@@ -483,8 +483,8 @@ public sealed class S7DriverReconnectTests
     }
 
     /// <summary>
-    ///     #630 — a second <c>InitializeAsync</c> on a live driver (no <c>ShutdownAsync</c> between, as
-    ///     <c>DriverInstanceActor.AdoptConfigDuringInit</c> does) must stop the first probe loop and
+    ///     #630 — a second <c>InitializeAsync</c> on a live driver (no <c>ShutdownAsync</c> between — the
+    ///     <c>IDriver</c> contract allows it) must stop the first probe loop and
     ///     dispose the first connection rather than orphan them.
     /// </summary>
     [Fact]

tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/Drivers/CalculationDependencyFlowTests.cs

@@ -31,7 +31,7 @@ public sealed class CalculationDependencyFlowTests : RuntimeActorTestBase
         return new RawTagEntry(rawPath, json, WriteIdempotent: false);
     }
 
-    /// <summary>Build the merged DriverConfig JSON the ApplyDelta path re-binds from (mirrors the deploy
+    /// <summary>Build the merged DriverConfig JSON an in-place re-bind reads (mirrors the deploy
     /// artifact folding the driver's RawTags into DriverInstanceSpec.DriverConfig).</summary>
     private static string ConfigJson(params RawTagEntry[] tags) =>
         System.Text.Json.JsonSerializer.Serialize(new { rawTags = tags });
@@ -130,7 +130,7 @@ public sealed class CalculationDependencyFlowTests : RuntimeActorTestBase
             published.ShouldContain(e => e.FullReference == "calc/remove" && Equals(e.Snapshot.Value, 7.0));
         }, PresenceBudget, TimeSpan.FromMilliseconds(100));
 
-        // ---- REDEPLOY (in-place ApplyDelta) ----
+        // ---- IN-PLACE RE-BIND (driver ReinitializeAsync) ----
         // New authored set: "keep" script EDITED to src/a*1000; "add" is a NEW tag reading a NEW dep src/b;
         // "remove" is dropped entirely.
         var newConfig = ConfigJson(
@@ -141,8 +141,9 @@ public sealed class CalculationDependencyFlowTests : RuntimeActorTestBase
         // The rebuilt dependency-ref set reflects the NEW authored tags (src/a from keep, src/b from add).
         driver.DependencyRefs.OrderBy(r => r).ShouldBe(new[] { "src/a", "src/b" });
 
-        // Part 2 sequencing: the host re-registers the adapter AFTER reinit (DeltaApplied → HandleDeltaApplied).
-        // Mirror that here — re-register so the adapter adopts the NEW ref set (incl. the brand-new src/b).
+        // The adapter re-reads the driver's refs only when told to; re-register AFTER the reinit so it adopts the
+        // NEW ref set (incl. the brand-new src/b). (The runtime respawns on a config change, #665, so a fresh
+        // adapter registers the new set in PreStart; this exercises the driver + adapter contract directly.)
         adapter.Tell(new DependencyConsumerMuxAdapter.ReRegister());
 
         // Leg 2 — after redeploy: the NEW dep src/b flows + the NEW tag computes; the EDITED script serves the

tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/Drivers/DriverInstanceActorNativeAlarmTests.cs

@@ -369,56 +369,6 @@ public sealed class DriverInstanceActorNativeAlarmTests : RuntimeActorTestBase
             .Connected.ShouldBeTrue();
     }
 
-    /// <summary>
-    ///     Gitea #663 — an in-place config change on a Connected driver (<see cref="DriverInstanceActor.ApplyDelta"/>
-    ///     → <see cref="IDriver.ReinitializeAsync"/>) must end with exactly one live data subscription and one live
-    ///     native-alarm subscription at the driver, and the alarm feed still forwarding. The handler used to keep
-    ///     the actor's handles across the reinit while the driver had dropped the subscriptions behind them, so
-    ///     the reconcile (which only re-subscribes a MISSING handle) never restored them and the driver went silent.
-    /// </summary>
-    /// <param name="reinitKeepsSubscriptions">false = the production shape (reinit drops everything, #630) —
-    /// the regression; true = a driver that keeps them, which pins that the fix releases before re-subscribing
-    /// instead of piling a second subscription on top.</param>
-    [Theory]
-    [InlineData(false)]
-    [InlineData(true)]
-    public void An_in_place_ApplyDelta_leaves_one_live_data_and_one_live_alarm_subscription(bool reinitKeepsSubscriptions)
-    {
-        var driver = new AlarmSourceStubDriver { ReinitKeepsSubscriptions = reinitKeepsSubscriptions };
-        var publisher = new CountingHealthPublisher();
-        var parent = CreateTestProbe();
-        parent.IgnoreMessages(m => m is DriverInstanceActor.ConnectivityChanged);
-        var actor = parent.ChildActorOf(DriverInstanceActor.Props(
-            driver, healthPublisher: publisher, healthPollInterval: TimeSpan.FromMilliseconds(100)));
-
-        actor.Tell(new DriverInstanceActor.SetDesiredSubscriptions(
-            new[] { "tag-a" }, TimeSpan.FromMilliseconds(100), new[] { "Temp.HiHi" }));
-        actor.Tell(new DriverInstanceActor.InitializeRequested("{}"));
-        AwaitCondition(() => driver.LiveDataSubscriptions == 1 && driver.LiveAlarmSubscriptions == 1, PresenceBudget);
-
-        var correlation = CorrelationId.NewId();
-        actor.Tell(new DriverInstanceActor.ApplyDelta("{\"changed\":true}", correlation), parent.Ref);
-        parent.FishForMessage<DriverInstanceActor.ApplyResult>(r => r.Correlation == correlation, PresenceBudget)
-            .Success.ShouldBeTrue();
-        driver.ReinitializeCount.ShouldBe(1);
-        driver.InitializeCount.ShouldBe(1, "an in-place delta must not go through the reconnect path");
-
-        AwaitCondition(() => driver.LiveDataSubscriptions == 1 && driver.LiveAlarmSubscriptions == 1, PresenceBudget);
-        // The "not two" half is an absence, so wait for three more health-poll ticks — each runs the reconcile
-        // that would issue a duplicate — before re-checking.
-        var ticks = publisher.Count;
-        AwaitCondition(() => publisher.Count >= ticks + 3, PresenceBudget);
-        driver.LiveDataSubscriptions.ShouldBe(1);
-        driver.LiveAlarmSubscriptions.ShouldBe(1);
-        driver.AlarmSubscriberCount.ShouldBe(1);
-
-        driver.RaiseAlarm(new AlarmEventArgs(
-            new StubAlarmHandle(), "Temp.HiHi", "Temp.HiHi", "T", "after reinit", AlarmSeverity.High,
-            DateTime.UtcNow, Kind: AlarmTransitionKind.Raise));
-        parent.FishForMessage<DriverInstanceActor.AttributeAlarmPublished>(_ => true, PresenceBudget)
-            .Args.ConditionId.ShouldBe("Temp.HiHi");
-    }
-
     // --- stub drivers ----------------------------------------------------------------------------
 
     private class StubDriver : IDriver
@@ -439,7 +389,7 @@ public sealed class DriverInstanceActorNativeAlarmTests : RuntimeActorTestBase
         }
 
         /// <summary>Reinitializes the driver.</summary>
-        public virtual Task ReinitializeAsync(string driverConfigJson, CancellationToken cancellationToken) =>
+        public Task ReinitializeAsync(string driverConfigJson, CancellationToken cancellationToken) =>
             Task.CompletedTask;
 
         /// <summary>Shuts down the driver.</summary>
@@ -463,55 +413,14 @@ public sealed class DriverInstanceActorNativeAlarmTests : RuntimeActorTestBase
         /// <summary>Number of live subscribers on <see cref="OnAlarmEvent"/> — proves attach/detach.</summary>
         public int AlarmSubscriberCount => OnAlarmEvent?.GetInvocationList().Length ?? 0;
 
-        private readonly object _liveLock = new();
-        private readonly HashSet<object> _liveData = new(ReferenceEqualityComparer.Instance);
-        private readonly HashSet<object> _liveAlarms = new(ReferenceEqualityComparer.Instance);
-        private int _reinitializeCount;
-
-        /// <summary>Driver-side data subscriptions currently open (subscribed and not yet released).</summary>
-        public int LiveDataSubscriptions { get { lock (_liveLock) return _liveData.Count; } }
-
-        /// <summary>Driver-side native-alarm subscriptions currently open.</summary>
-        public int LiveAlarmSubscriptions { get { lock (_liveLock) return _liveAlarms.Count; } }
-
-        /// <summary>Number of <see cref="ReinitializeAsync"/> calls.</summary>
-        public int ReinitializeCount => Volatile.Read(ref _reinitializeCount);
-
-        /// <summary>When false (the default, and every production driver since #630), a reinit releases the
-        /// device/session state and with it every driver-side subscription; when true it keeps them — the
-        /// shape that would double-subscribe if the actor re-subscribed without releasing first.</summary>
-        public bool ReinitKeepsSubscriptions { get; init; }
-
-        /// <inheritdoc />
-        public override Task ReinitializeAsync(string driverConfigJson, CancellationToken cancellationToken)
-        {
-            Interlocked.Increment(ref _reinitializeCount);
-            if (!ReinitKeepsSubscriptions)
-            {
-                lock (_liveLock)
-                {
-                    _liveData.Clear();
-                    _liveAlarms.Clear();
-                }
-            }
-            return Task.CompletedTask;
-        }
-
         /// <summary>Subscribes to the specified full references.</summary>
         public Task<ISubscriptionHandle> SubscribeAsync(
-            IReadOnlyList<string> fullReferences, TimeSpan publishingInterval, CancellationToken cancellationToken)
-        {
-            var handle = new StubHandle();
-            lock (_liveLock) _liveData.Add(handle);
-            return Task.FromResult<ISubscriptionHandle>(handle);
-        }
+            IReadOnlyList<string> fullReferences, TimeSpan publishingInterval, CancellationToken cancellationToken) =>
+            Task.FromResult<ISubscriptionHandle>(_subHandle);
 
         /// <summary>Unsubscribes from the specified subscription handle.</summary>
-        public Task UnsubscribeAsync(ISubscriptionHandle handle, CancellationToken cancellationToken)
-        {
-            lock (_liveLock) _liveData.Remove(handle);
-            return Task.CompletedTask;
-        }
+        public Task UnsubscribeAsync(ISubscriptionHandle handle, CancellationToken cancellationToken) =>
+            Task.CompletedTask;
 
         private int _subscribeAlarmsCallCount;
 
@@ -530,9 +439,7 @@ public sealed class DriverInstanceActorNativeAlarmTests : RuntimeActorTestBase
             var call = Interlocked.Increment(ref _subscribeAlarmsCallCount);
             if (call <= AlarmSubscribeFailuresBeforeSuccess)
                 throw new InvalidOperationException($"alarm subscribe failure {call} (test-injected)");
-            var handle = new StubAlarmHandle();
-            lock (_liveLock) _liveAlarms.Add(handle);
-            return Task.FromResult<IAlarmSubscriptionHandle>(handle);
+            return Task.FromResult<IAlarmSubscriptionHandle>(new StubAlarmHandle());
         }
 
         /// <summary>How many leading <see cref="SubscribeAlarmsAsync"/> calls throw — the "session not ready
@@ -540,11 +447,8 @@ public sealed class DriverInstanceActorNativeAlarmTests : RuntimeActorTestBase
         public int AlarmSubscribeFailuresBeforeSuccess { get; init; }
 
         /// <summary>Cancels an alarm subscription.</summary>
-        public Task UnsubscribeAlarmsAsync(IAlarmSubscriptionHandle handle, CancellationToken cancellationToken)
-        {
-            lock (_liveLock) _liveAlarms.Remove(handle);
-            return Task.CompletedTask;
-        }
+        public Task UnsubscribeAlarmsAsync(IAlarmSubscriptionHandle handle, CancellationToken cancellationToken) =>
+            Task.CompletedTask;
 
         /// <summary>Acknowledges a batch of alarms.</summary>
         public Task AcknowledgeAsync(

tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/Drivers/DriverInstanceActorTests.cs

@@ -11,28 +11,6 @@ namespace ZB.MOM.WW.OtOpcUa.Runtime.Tests.Drivers;
 
 public sealed class DriverInstanceActorTests : RuntimeActorTestBase
 {
-    /// <summary>Verifies that ApplyDelta calls ReinitializeAsync when connected and replies success.</summary>
-    [Fact]
-    public async Task ApplyDelta_when_Connected_calls_ReinitializeAsync_and_replies_success()
-    {
-        var driver = new StubDriver();
-        var actor = Sys.ActorOf(DriverInstanceActor.Props(driver));
-
-        // Drive: Initialize → Connected.
-        actor.Tell(new DriverInstanceActor.InitializeRequested("{}"));
-        AwaitCondition(() => driver.InitializeCount > 0, TimeSpan.FromSeconds(2));
-
-        // Issue ApplyDelta and capture the reply via Ask.
-        var correlation = CorrelationId.NewId();
-        var reply = await actor.Ask<DriverInstanceActor.ApplyResult>(
-            new DriverInstanceActor.ApplyDelta("{\"changed\":true}", correlation),
-            TimeSpan.FromSeconds(3));
-
-        reply.Success.ShouldBeTrue();
-        reply.Correlation.ShouldBe(correlation);
-        driver.ReinitializeCount.ShouldBe(1);
-    }
-
     /// <summary>Verifies that initialize failure keeps the actor in Reconnecting state.</summary>
     [Fact]
     public void Initialize_failure_keeps_actor_in_Reconnecting_state()
@@ -305,109 +283,6 @@ public sealed class DriverInstanceActorTests : RuntimeActorTestBase
         parent.ExpectNoMsg(TimeSpan.FromMilliseconds(300));
     }
 
-    /// <summary>A driver stuck Reconnecting (init failing on a bad config) adopts a corrected config
-    /// delivered via ApplyDelta and connects on it — no node restart. Closes pending.md #7.</summary>
-    [Fact]
-    public async Task ApplyDelta_while_Reconnecting_adopts_new_config_and_connects()
-    {
-        const string bad = "{\"v\":\"bad\"}";
-        const string good = "{\"v\":\"good\"}";
-        var driver = new SubscribableStubDriver
-        {
-            InitBehavior = cfg => cfg == good ? Task.CompletedTask : throw new InvalidOperationException("bad-cfg"),
-        };
-        var parent = CreateTestProbe();
-        // #477: DriverInstanceActor now Tells the parent ConnectivityChanged on each connect/
-        // disconnect; these tests assert on the data/alarm/discovery forwards, so ignore it.
-        parent.IgnoreMessages(m => m is DriverInstanceActor.ConnectivityChanged);
-        var actor = parent.ChildActorOf(DriverInstanceActor.Props(driver, reconnectInterval: TimeSpan.FromMilliseconds(50)));
-
-        actor.Tell(new DriverInstanceActor.SetDesiredSubscriptions(new[] { "tag-a" }, TimeSpan.FromMilliseconds(100)));
-
-        actor.Tell(new DriverInstanceActor.InitializeRequested(bad));
-        AwaitCondition(() => driver.InitializeCount >= 2, TimeSpan.FromSeconds(2));
-        driver.SubscribeCount.ShouldBe(0);
-
-        var correlation = CorrelationId.NewId();
-        var reply = await actor.Ask<DriverInstanceActor.ApplyResult>(
-            new DriverInstanceActor.ApplyDelta(good, correlation), TimeSpan.FromSeconds(3));
-        reply.Success.ShouldBeTrue();
-        reply.Correlation.ShouldBe(correlation);
-
-        AwaitCondition(() => driver.SubscribeCount >= 1, TimeSpan.FromSeconds(3));
-        driver.InitConfigs.ShouldContain(good);
-    }
-
-    /// <summary>
-    ///     Gitea #664 — a mid-connect adoption sends <see cref="DriverInstanceActor.DeltaApplied"/> once the
-    ///     driver has initialised on the ADOPTED config, so the host re-registers a dependency consumer's mux
-    ///     interest (the Calculation driver's refs change with its tag set). It used to send nothing, leaving the
-    ///     old interest registered. The notification is one-shot: a later reconnect on the same config sends none.
-    /// </summary>
-    [Fact]
-    public void A_mid_connect_adoption_notifies_DeltaApplied_once_after_the_adopted_init_succeeds()
-    {
-        const string bad = "{\"v\":\"bad\"}";
-        const string good = "{\"v\":\"good\"}";
-        var driver = new SubscribableStubDriver
-        {
-            InitBehavior = cfg => cfg == good ? Task.CompletedTask : throw new InvalidOperationException("bad-cfg"),
-        };
-        var parent = CreateTestProbe();
-        parent.IgnoreMessages(m => m is not DriverInstanceActor.DeltaApplied);
-        var actor = parent.ChildActorOf(DriverInstanceActor.Props(driver, reconnectInterval: TimeSpan.FromMilliseconds(50)));
-        actor.Tell(new DriverInstanceActor.SetDesiredSubscriptions(new[] { "tag-a" }, TimeSpan.FromMilliseconds(100)));
-
-        actor.Tell(new DriverInstanceActor.InitializeRequested(bad));
-        AwaitCondition(() => driver.InitializeCount >= 2, PresenceBudget);
-
-        actor.Tell(new DriverInstanceActor.ApplyDelta(good, CorrelationId.NewId()));
-        parent.ExpectMsg<DriverInstanceActor.DeltaApplied>(PresenceBudget);
-        driver.InitConfigs.ShouldContain(good, "the notification must follow an init on the adopted config");
-
-        // A reconnect on the same config re-runs InitializeSucceeded; the positive control is its re-subscribe.
-        var subscribes = driver.SubscribeCount;
-        actor.Tell(new DriverInstanceActor.ForceReconnect());
-        AwaitCondition(() => driver.SubscribeCount > subscribes, PresenceBudget);
-        parent.ExpectNoMsg(TimeSpan.FromMilliseconds(300));
-    }
-
-    /// <summary>A stale InitializeSucceeded from an old (superseded) config cannot hijack the state:
-    /// while a gated old-config init is pending in Connecting, an ApplyDelta adopts a new config; the
-    /// old init completing afterwards is ignored, and only the new config drives Connected.</summary>
-    [Fact]
-    public async Task ApplyDelta_supersedes_in_flight_init_so_stale_result_is_ignored()
-    {
-        const string v1 = "{\"v\":1}";
-        const string v2 = "{\"v\":2}";
-        var gate1 = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
-        var gate2 = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
-        var driver = new SubscribableStubDriver
-        {
-            InitBehavior = cfg => cfg == v1 ? gate1.Task : gate2.Task,
-        };
-        var parent = CreateTestProbe();
-        // #477: DriverInstanceActor now Tells the parent ConnectivityChanged on each connect/
-        // disconnect; these tests assert on the data/alarm/discovery forwards, so ignore it.
-        parent.IgnoreMessages(m => m is DriverInstanceActor.ConnectivityChanged);
-        var actor = parent.ChildActorOf(DriverInstanceActor.Props(driver, reconnectInterval: TimeSpan.FromSeconds(30)));
-        actor.Tell(new DriverInstanceActor.SetDesiredSubscriptions(new[] { "tag-a" }, TimeSpan.FromMilliseconds(100)));
-
-        actor.Tell(new DriverInstanceActor.InitializeRequested(v1));
-        AwaitCondition(() => driver.InitConfigs.Contains(v1), TimeSpan.FromSeconds(2));
-
-        await actor.Ask<DriverInstanceActor.ApplyResult>(
-            new DriverInstanceActor.ApplyDelta(v2, CorrelationId.NewId()), TimeSpan.FromSeconds(3));
-        AwaitCondition(() => driver.InitConfigs.Contains(v2), TimeSpan.FromSeconds(2));
-
-        gate1.SetResult();
-        parent.ExpectNoMsg(TimeSpan.FromMilliseconds(400));
-        driver.SubscribeCount.ShouldBe(0);
-
-        gate2.SetResult();
-        AwaitCondition(() => driver.SubscribeCount >= 1, TimeSpan.FromSeconds(3));
-    }
-
     /// <summary>
     ///     Archreview <b>03/S15 (T11)</b> — a child that is <b>stopped</b> announces comms loss on its way
     ///     out, so the host latches its value nodes <c>BadNoCommunication</c>.

tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/Drivers/DriverSpawnPlannerTests.cs

@@ -19,7 +19,6 @@ public sealed class DriverSpawnPlannerTests
         var plan = DriverSpawnPlanner.Compute(current, target);
 
         plan.ToSpawn.Count.ShouldBe(2);
-        plan.ToApplyDelta.ShouldBeEmpty();
         plan.ToStop.ShouldBeEmpty();
     }
 
@@ -36,7 +35,6 @@ public sealed class DriverSpawnPlannerTests
         var plan = DriverSpawnPlanner.Compute(current, target);
 
         plan.ToSpawn.ShouldBeEmpty();
-        plan.ToApplyDelta.ShouldBeEmpty();
         plan.ToStop.ShouldBeEmpty();
     }
 
@@ -65,7 +63,6 @@ public sealed class DriverSpawnPlannerTests
         plan.ToSpawn.Single().DriverInstanceId.ShouldBe("a");
         plan.ToSpawn.Single().DriverConfig.ShouldBe("{\"host\":\"new\"}");
         // The whole point: nothing is left on the in-place path that could discard the edit.
-        plan.ToApplyDelta.ShouldBeEmpty();
     }
 
     /// <summary>Verifies that removed drivers are routed to ToStop.</summary>
@@ -83,7 +80,6 @@ public sealed class DriverSpawnPlannerTests
 
         plan.ToStop.ShouldBe(new[] { "b" });
         plan.ToSpawn.ShouldBeEmpty();
-        plan.ToApplyDelta.ShouldBeEmpty();
     }
 
     /// <summary>Verifies that disabled drivers with running children are routed to ToStop.</summary>
@@ -100,7 +96,6 @@ public sealed class DriverSpawnPlannerTests
 
         plan.ToStop.Single().ShouldBe("a");
         plan.ToSpawn.ShouldBeEmpty();
-        plan.ToApplyDelta.ShouldBeEmpty();
     }
 
     /// <summary>Verifies that disabled new drivers are not spawned.</summary>
@@ -113,7 +108,6 @@ public sealed class DriverSpawnPlannerTests
         var plan = DriverSpawnPlanner.Compute(current, target);
 
         plan.ToSpawn.ShouldBeEmpty();
-        plan.ToApplyDelta.ShouldBeEmpty();
         plan.ToStop.ShouldBeEmpty();
     }
 
@@ -131,7 +125,6 @@ public sealed class DriverSpawnPlannerTests
 
         plan.ToStop.Single().ShouldBe("a");
         plan.ToSpawn.Single().DriverType.ShouldBe("AbCip");
-        plan.ToApplyDelta.ShouldBeEmpty();
     }
 
     /// <summary>
@@ -153,7 +146,6 @@ public sealed class DriverSpawnPlannerTests
 
         plan.ToStop.Single().ShouldBe("a");
         plan.ToSpawn.Single().DriverInstanceId.ShouldBe("a");
-        plan.ToApplyDelta.ShouldBeEmpty();
     }
 
     /// <summary>
@@ -173,7 +165,6 @@ public sealed class DriverSpawnPlannerTests
 
         plan.ToStop.Single().ShouldBe("a");
         plan.ToSpawn.Single().DriverInstanceId.ShouldBe("a");
-        plan.ToApplyDelta.ShouldBeEmpty();
     }
 
     /// <summary>
@@ -196,6 +187,5 @@ public sealed class DriverSpawnPlannerTests
 
         plan.ToStop.Single().ShouldBe("a");
         plan.ToSpawn.Single().DriverInstanceId.ShouldBe("a");
-        plan.ToApplyDelta.ShouldBeEmpty();
     }
 }