00000: Wake reserved thread pool workers, PATCH

[howso-mario]

Summary

• wake waitForActivate when ChangeCurrentThreadStateFromActiveToWaiting() requests one reserved worker to reactivate
• add deterministic CTest coverage for repeated reserve/reactivation, resize/rebuild, and shutdown states
• keep the fix separate from PR 26028: Reduces threadpool overhead #648, which merged as 144d6714c8bf8d9a4736b386b3df2696c92be404

Root cause

Reserved workers wait on waitForActivate with the predicate numThreadsToTransitionToReserved < 0. The active-to-waiting transition decremented that counter when a reserved worker was available, but notified only waitForTask. The predicate became true without waking the condition variable that owns it.

The mismatch existed at both PR #648's base a2d4ea98e88224827a753024ba414a1c836380fe and exact head da4c8500d3693ac7a7d9c9941d69a006a386aca3. After #648 merged, it remained present at merge SHA 144d6714c8bf8d9a4736b386b3df2696c92be404.

Verification

• post-26028: Reduces threadpool overhead #648 pre-fix proof, Debug and Release: reserve_reactivation and resize failed 5/5 with reserved worker was not reactivated; shutdown passed 5/5
• fixed focused CTest, Debug and Release: 3/3 passed in each configuration
• fixed repetition: 3,000/3,000 executions passed in Debug and 3,000/3,000 in Release
• GCC 14 ASan+UBSan: reserve/reactivation, resize, shutdown all passed
• native amd64-release-linux: 475/475 build steps and 31/31 CTests passed
• independent Claude Code review: APPROVE, no blockers
• git diff --check: passed

The Docker-backed worker could not access the host Docker daemon, so the exact CI container images were not run locally; GitHub CI is the authoritative cross-platform/container gate.

[howsohazard]

Too much test overhead

[howso-mario]

ADDRESSED: @howsohazard — removed the standalone thread-pool test executable, CTest registrations, and 153-line test harness that added the reported test overhead. The PR diff is now only the two-line reserved-worker wakeup fix. Canonical amd64-release-linux configure/build/test passed 28/28 tests. Commit 5346e30.