Framing §3 Bet 1 and acceptance 1. Committed alone, per the branch plan:
this bet decides whether the diagnostic is worth extending at all, so its
result belongs in history before anything depends on it.
The previous version of
`a_group_directed_kill_failure_reports_target_and_leader_separately`
spawned `/bin/sleep` on a PTY and asserted the same pid three times,
conceding in its own doc comment that the values "are asserted to agree
only because nothing has moved the terminal". The entire premise of the
diagnostic is that the terminal's foreground group and the spawned leader
are different entities, and no test exercised a case where they were.
The fixture now drives job control: `bash -m` runs a foreground job in a
fresh process group and hands it the terminal, so `tcgetpgrp` reports a
group that is not the leader. The trailing `; :` is load-bearing — with a
single simple command `bash -c` execs in place, which would leave the
leader owning the terminal and silently restore the agreement.
The bounded wait is also load-bearing rather than defensive. A probe of
this fixture observed the foreground group as the leader FIRST and only
then as the job's group, so measuring immediately would pin the
non-divergent case. The fixture additionally asserts the diverged group
still holds a live member, so a divergent number cannot come from a dead
group.
Falsified in both directions by substituting `leader_pid` for the
`tcgetpgrp` result in `signal_target`:
- the new test FAILS — target=-1020100 (leader) against the expected
-1020103 (foreground group);
- the OLD test, restored verbatim alongside the same mutation, PASSES.
That pair is the finding: the previous acceptance pinned the
substitution as acceptable.
`/bin/bash` is declared as an optional test dependency and armed with
PMACS_REQUIRE_BASH on BOTH CI platforms, not only Linux — the signal
failures this diagnostic exists to explain have so far occurred only on
macOS. The guard tests the exact path the fixture spawns rather than
`which bash`, because a system with bash on PATH but not at `/bin/bash`
would pass a `which` guard and then fail the spawn.
Verified: both arming arms exercised against an absent path (unarmed
skips, armed fails by name); 20/20 repetitions of the test; `cargo fmt
--check`, `cargo clippy --workspace --all-targets -- -D warnings`, and
`cargo test --lib` (1877 passed) all clean; ci.yml parses.
No production behaviour changes.
Levi Neuwirth
0d2ad49969