[Tynwink2000]

Summary

• Measure context check --all concurrency at the client RoundTripper boundary, decrementing the in-flight counter before a call returns.
• Retain the four-worker upper-bound assertion and verify that all six context outcomes are returned and every client call finishes.
• Separate real HTTP timeout coverage from worker-count assertions. Remote handler cancellation and cleanup can lag behind client timeout completion and are not a reliable measure of occupied client workers.
• Keep CLI runtime behavior unchanged; no increased timeout, relaxed concurrency limit, or arbitrary sleep is introduced.

Validation

• Repeated both check-all regression tests 100 times.
• Repeated both regression tests 100 times with the race detector.
• make check (formatting, vet, and full race-enabled test suite).
• CLI build.