`posix_spawnp` and `fork` both fail with EAGAIN when the process table or a
per-user limit is momentarily full. Both paths treated that as a hard failure,
so a burst of process creation turned into CBM_PROC_SPAWN_FAILED — a git probe,
an LSP server, or an index worker refusing to run for a reason the user can
neither see nor act on, on a machine that is merely busy.
This is the production half of a flake we have been re-running for two days:
`subprocess_run_clean` failed spawning `/bin/sh -c "exit 0"` on macOS runners in
three separate CI runs, always under a loaded release matrix, always green on a
quiet rerun. Chasing it as a test race would have been chasing the symptom — the
test is right, and a user on a loaded laptop hits the same edge.
EAGAIN/ENOMEM now retry three times over ~30ms; everything else keeps failing
immediately, and an exhausted system still fails after the backoff rather than
spinning. exec-class errors (ENOENT/EACCES/ENOEXEC/...) are untouched, so the
documented "missing binary exits 127, spawn_failed means the mechanism failed"
contract still holds. The fork fallback gets the same treatment: it fails for
the same reason under the same pressure, and the fallback must not be less
robust than the primary path.
Signed-off-by: Martin Vogel <martin.vogel.tech@gmail.com>
Martin Vogel
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