- 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
Joseph Doherty