* fix(control-socket): recover from transient accept errors
Keep the control socket alive when Darwin reports a transient fcntl failure while accepting a client connection.
Refs #1346
* test(control-socket): use synchronous pipeline lookup
* test(control-socket): query handler on event loop
* fix(control-socket): preserve channel backpressure
* test(control-socket): exercise accept error recovery
* test(control-socket): verify accepts continue after transient errors
Check that the real server inbound stream yields a client connection after
each simulated accept error. Keep the read-routing and unrelated-error
checks, bound the wait, and close the test connections.
Adapted from the regression test suggested in:
https://github.com/openai/tart/pull/1351#issuecomment-5851285933
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Co-authored-by: Yibo Zhuang <yzhuang@openai.com>
