- ShadowScriptRunner (Core.Scripting): IScriptShadow.Mirror copies the inputs and queues the shadow run on the
pool; compares value (structural), CLR type, status and failure class (compile / budget / threw+message /
unsupported_type); runner-fault shadow outcomes (Unavailable, worker busy) are not compared. Bounded:
Scripting:Shadow:MaxInFlight (256) and one per script; drops counted (behind | key_busy).
- Metrics otopcua.script.shadow.{compared,mismatch{script},dropped,inflight}; one rate-limited Warning per
script and reason with a diff summary (Scripting:Shadow:MismatchLogsPerMinute, re-armed at the seam's deploy).
- The VirtualTag, Calculation and scripted-alarm seams recognise the shadow and keep their in-process path
byte-for-byte (no coalescer, one-at-a-time pump, in-process engine), mirroring after each compiled run.
- ScriptRunnerSelection builds the shadow over an OutOfProcessScriptRunner whose lines carry
ScriptRunnerRole=Shadow; Status() is null under Shadow so readiness never sees the shadow pool; the
script-runner health entry stays Healthy and reports the shadow counters as data.
- docker-dev/docker-compose.script-runner-shadow.yml; docs/VirtualTags.md "Shadow mode".
- Tests: comparison table, per-script metric + once-per-reason log, rate limit, hung/blocking/throwing shadow
never reaches the caller, MaxInFlight drop accounting, input copy; real-worker divergent + unsupported-type
scripts counted against exactly those scripts, a worker-only runaway killed/quarantined there with every
published value intact, alarm transitions identical to in process across a kill -9 of the shadow worker.
Mutation-proved (16 mutants, 15 red; the one survivor added an assertion).
Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV
Second P1 slice of docs/plans/2026-11-09-out-of-process-script-runner-design.md; still opt-in behind
Scripting:Runner=OutOfProcess (InProcess unchanged).
- Compiled-PE cache (design §7, §14 #8): Scripting:Worker:PeCacheDir holds <dir>/pe/<id>.pe entries authenticated
with HMAC-SHA256 under a per-node random key (<dir>/pe-cache.key, created by the host, 0600/0700 on Unix), handed to
the worker in Hello. Entry id = SHA-256(compile fingerprint + kind + source); the fingerprint covers the Roslyn
version, the Core.Scripting build (analyzer, wrapper, stack guard), the sandbox reference set and the runtime. Edited,
truncated, other-key or renamed entries are rejected, deleted and recompiled; the worker never loads unverified bytes.
Pruned by recency at startup (30 d / 50 000). ScriptEvaluator splits into CompileToImage + FromImage. Measured on
40 scripts, restart to every first result: macOS 820 ms no cache / 840 ms empty / 85 ms warm;
windev (Windows) 9.5 s / 9.4 s / 1.0 s.
- Quarantine race: WorkerConnection runs exit attribution synchronously BEFORE completing the evaluations/loads it held
(and before Exited), and the shard passes it straight to the runner — a kill strike is in place before the killed
key's slot is released.
- Supervision: a dead worker restarts by itself after its backoff; Unavailable outcomes carry ScriptRunOutcome.Recovery
(-> VirtualTagEvalResult.RetryWhen) and the VT actor / Calculation driver re-evaluate once against current inputs when
it completes. Isolation worker stops after Scripting:Worker:IsolationIdleTimeout (10 min). Keys compiling when a
worker dies are suspects too (isolation finds a poison compile and quarantines it). Startup orphan sweep by launch
marker: kills only a process whose marker's host is gone and whose pid + start time + image match.
- Crash-loop circuit (Scripting:Worker:CircuitOpenAfter, 2 min): runner Unavailable, one Error, evaluations answered
at once while shards keep retrying at the cap.
- Observability (§10): otopcua.script.runner.state, worker.up/inflight/queue_depth/heap_bytes (shard),
ipc.roundtrip + eval.duration (kind), compile{cache}, isolation.suspects, exits reason=idle. `script-runner` health
check on the ready tier, at worst Degraded (§14 #12: degraded but still ready).
Left on #780: self-contained worker publish, installer (account, pipe ACL, firewall), docker-dev live drill,
scripted-alarm seam, the §4.5 per-seam batch submit, the §8 perf harness.
Tests: SupervisionTests, PeCacheStoreTests/PeCacheWorkerTests (real workers), ScriptRunnerHealthCheckTests, VT + Calc
recovery seam tests; 14 mutations each turned their test red.
Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV
Joseph Doherty