[zhechen-cs]

A task that calls runtime.Goexit() skips subpoolWorker's queue handoff and worker bookkeeping. Its subpool retains a worker that no longer exists, so queued tasks never run and StopAndWait() blocks indefinitely. Nested subpools are affected as well.

Mirror the root worker's abnormal-exit cleanup in subpool workers: record the failed task, retire the worker when there is no queued work, or launch its replacement. The regression covers direct and nested subpools, subsequent task completion, shutdown and task counters.

Related to #135 and #137.

Validation (Go 1.26.9, macOS):

• Regression fails on unmodified 7b7c16a for both subpool layouts.
• New regression and existing Goexit tests pass with -race -count=10.
• make test-ci passes (go test -race -v -timeout 1m -count=3 ./...).
• go vet ./... and git diff --check pass.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.80%. Comparing base (7b7c16a) to head (da86f92).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #148      +/-   ##
==========================================
+ Coverage   95.75%   95.80%   +0.04%     
==========================================
  Files          11       11              
  Lines         613      620       +7     
==========================================
+ Hits          587      594       +7     
  Misses         23       23              
  Partials        3        3              

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[alitto]

Nice contribution 🙌 , thanks a lot!