[Qwejay]

Summary

• Protect shared runtime-variable reads/writes and loop counters with a dedicated reentrant lock; use snapshots for substitution and notifications.
• Protect node/error counters with a dedicated statistics lock and snapshot completion metrics safely.
• Serialize stop, pause, and resume transitions under the thread lock; stopping now atomically signals workers, releases paused workers, and clears queued nodes.
• Add run-generation guards so delayed UI cleanup from a completed run cannot reset or hide a newer run.
• Ensure startup initialization failures reset running, stop, pause, and queue state.
• Add regression coverage for startup cleanup, variable snapshots, stale callbacks, 40,000 concurrent statistic increments, and stop/pause/resume transitions.

Validation

• The previous CI run passed source compilation and all 17 regression tests.
• New stop/pause/resume synchronization tests are now committed; latest CI is pending.
• Windows GUI, full engine stress, node-by-node, and exported EXE tests remain necessary.