`OCIContainer.__enter__` was hardened in #2879 to always clean up on
failure, but `__exit__` was left unguarded. If the container/bash had
already died, `bash_stdin.write("exit 0")` raises `BrokenPipeError`; if
bash refuses to exit, `process.wait(timeout=30)` raises `TimeoutExpired`.
Either propagated out of `__exit__` before `_remove_container()` ran,
leaking the container (and, on timeout, the `start` process too).
Wrap the teardown so a broken pipe or timeout instead forces the process
down (kill + wait) and always falls through to container removal, while
still respecting CIBW_DEBUG_KEEP_CONTAINER. Pipe closes are now also
guarded so a flush-on-close against a dead pipe can't mask cleanup.
Add non-docker unit tests for the clean-exit, already-dead-bash, and
shutdown-timeout paths.
Assisted-by: ClaudeCode:claude-opus-4.8
Henry Schreiner
29888149e1