CI falsified framing Bet 1. Both macOS legs reported
job control never moved the terminal off the leader
(leader=8542, foreground groups observed: [8542])
with the terminal staying on the leader for the entire 10s bounded wait.
Linux diverges reliably — 20/20 locally and green on both ubuntu legs —
so this is a platform difference rather than a flake, and rerunning past
it would have been wrong.
The framing named this outcome and prescribed the response, so that is
what ships rather than an improvised fix:
- The divergent case is pinned by INJECTING the foreground group at the
`signal_target` seam. Deterministic, runs on every platform. The
injection seam widens from failure-only to either outcome; the branch,
target choice, leader observation against the real child, and report
construction all remain production code.
- Verified still discriminating: the `leader_pid`-substitution mutation
fails it, `target=-1707909` against an expected `-1707910`. That was
the whole point of the original rewrite and it survives the fallback.
- The real shell is retained as corroboration in
`job_control_really_diverges_the_foreground_group`, Linux-only. It
skips on macOS by PLATFORM CHECK rather than by arming: the
precondition genuinely does not hold there, so running it would assert
a false claim about macOS instead of finding a bug.
- Framing revision 5 records the falsification and states exactly how
the injected pin is weaker — it proves the target is read from the
lookup rather than substituted from the leader; it does not by itself
prove any real shell produces that divergence.
`PMACS_REQUIRE_BASH` moves to Linux-only. The earlier reasoning for
arming both platforms — macOS is where the failures happen, so Linux-only
leaves it dark where it matters — was right about the diagnostic and
wrong about this test, which cannot produce its precondition on macOS at
all. Arming it there made a missing binary fatal for a test that can
never run. The measurement is recorded in ci.yml and the README so it is
not re-derived.
Gates on this tree: 11 gates, 4471 tests, zero failures.
Levi Neuwirth
66f73013fc