The soft deadline T was armed on the host at submit, so the pipe round trip
and the time a starved worker waits to be scheduled counted against the
script: under load a trivial script reported 'script timed out', in Shadow
mode that was a script mismatch, and at T + G the host killed the worker and
struck the key.
- Protocol (additive, negotiated): Hello/Ready.worker_soft_clock and
EvalResults.soft_expired_eval_ids. protocol_version stays 1; a worker that
does not echo the flag keeps the pre-#827 host clock.
- Worker: the watchdog runs each run's soft clock from the moment an
evaluation thread starts it and reports the crossing (woken early for
budgets shorter than its 50 ms poll). It still never cancels by itself;
its fail-fast is anchored at the soft notice + G + margin.
- Host (PendingEval): the soft notice answers the caller and arms the kill G
later. The host's own timer becomes a transport deadline, T + G from submit
(restarted at a deferred run's start); passing it with no result and no
notice yields TransportTimedOut -> Unavailable 'script worker unresponsive'
(BadResourceUnavailable, recovery = the run's completion), no strike, no
kill, no Cancel. A re-trigger refused by that still-unanswered run is
Unavailable too, not 'previous run still running'. Counted as
otopcua.script.ipc.timeouts{kind}.
- Frame writer: coalescing now carries soft_expired_eval_ids (it silently
dropped them); the host processes soft notices before results in a frame.
- Shadow: unresponsive is shadow_unavailable (Unavailable), never a mismatch.
Tests: WorkerSoftClockTests suspends the real worker (SIGSTOP via libc kill /
NtSuspendProcess) - a stall past T still returns 7; a stall past T + G is a
runner fault with nothing struck; a late-starting runaway is still timed out
at T from its start and killed G after; Shadow stays match /
shadow_unavailable; both clocks enforce T and G; PendingEval state machine.
- 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