A docs-only PR (#172) failed Test (macos-latest / luajit) on
acc28_child_input_and_the_c_c_escape_work_unchanged_in_a_panel with
"kill: EPERM: Operation not permitted" raised out of terminate. A docs
diff cannot cause that, main was green at the PR's exact base, and three
other PRs passed the same job.
This framing reaches revision 4 after three review rounds, and what it
proposes is much smaller than what it started with. Revisions 1 to 3 each
proposed a tolerance rule -- treat some errno as success -- and each was
unsound in the same way: they concluded something about a process from
something that was not about that process. Revision 1 concluded from an
errno alone, which says only that a syscall failed. Revision 2 concluded
from the spawned leader while a PTY signal targets the tty's foreground
process group, which diverges from the leader exactly when job control is
in use. Revision 3 corrected EPERM but kept group-directed ESRCH, which
proves only that the selected foreground group vanished, not that the
leader exited.
So no tolerance rule lands. The disposition is preserved exactly: every
failing call still fails, with no state transition and no ledger arming.
What lands is that the failure explains itself, recording the target
source and value, the spawn-time pgid or leader pid, the errno, and the
leader's real try_wait state as five separate facts. Every candidate fix
is decidable from those together and none is decidable from the errno
alone.
Two claims are stated more narrowly than earlier revisions had them.
Consulting try_wait reaps an exited child and caches its status, so this
is not "strictly additive" -- it is "no disposition change", with an
event-count test pinning that poll_one still emits exactly one exit
event. And the test seam injects the kill attempt's result only, never
the observation, so the real ChildHandle::try_wait runs against the real
child; a stubbed observation would bypass the path under test.
Parked with their reasons: all tolerance rules, terminate becoming
idempotent for an already-reaped process (an independent fix answering a
different failure), and signal_target's read-then-kill of tcgetpgrp,
which is the most likely real fix site.
The lane closes when this lands rather than waiting for the flake to
recur; the next occurrence carries its own evidence under whoever's PR.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HZjWMjwPXhPbt9upku9mCk
Levi Neuwirth
dd581cd90c