Closes out task-group 1 (the commit-engine event-driven-resolve
keystone). Pure test-only: real pthreads racing the admission gate,
the sweep thread, and commit_on_ack, not sequential calls dressed as
concurrent. Adds the genuine two-real-thread ack-vs-sweep-thread race
both task-1.3 review rounds flagged as a nice-to-have (the existing
race test only proved the tie-break via single-thread white-box state
manipulation).
Also resolves the bug-1407 saga: task 1.4's "closed, 70/70" and this
task's initial "reopened, 10/10 failing" were both correct,
contradictory measurements of the identical source commit. Root cause
was a stale incremental-build artifact in the shared build/ directory
(ninja -C build rebuilt incrementally across 5 sequential tasks
without ever a fresh meson setup) -- not a source regression. Proven
by isolating each measurement in a throwaway git worktree with a
fresh build. bug-1407 is genuinely closed; the incremental-build
staleness gotcha is now documented in cerebrum.md for the remaining
task series.
Rongsong Shen
2d9f1e947a