ShadowModeTests' runaway case asserted "slowest < 250 ms" around evaluations
whose timing included cold Roslyn compile/JIT of new script text, so it failed
on a healthy published path (540-880 ms measured, both SDK baselines).
The test now puts a test-owned barrier runner (GatedShadow) between the real
ShadowScriptRunner and the real worker pool. The runaway's first shadow run is
held before it reaches the pool, then (after it runs away in the worker, the
pool answers T and the worker is KilledDeadline with the runaway as culprit)
its outcome is held before comparison. Published evaluations made while a
barrier is closed must return the in-process values; a Mirror that waited for
its shadow hangs into a 30 s liveness failure (mutation-checked). Output
correctness, pool kill/quarantine, published-side never quarantined, the single
runaway mismatch (sibling is a victim, not compared) and key_busy drops are kept.
The wall-clock number moves to an opt-in Category=Perf case
(Shadow_published_path_latency_while_the_shadow_runs_away, OTOPCUA_SCRIPT_PERF=1)
on warmed evaluators, reporting hardware and load average.
Sibling: ContainmentTests' hard-deadline case timed the runaway's first
(cold-compile) run; it now compiles the runaway's source first with an input
that does not spin.
Joseph Doherty