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Neil
f35015d0c8
The orphan-relay-PTY sweep authorizes `pty.shutdown { immediate: true }`, which
runs `forceKillPosixPtyProcessGroups`: collect every process group on the pane's
tty, then `killpg` each one. The blast radius is therefore (groups on the tty) x
(members of those groups, wherever they are). The idleness evidence measured only
the first factor, so three shapes read as idle and were SIGKILLed:
- with job control off (`set +m`) a background job keeps the SHELL's pgid, so the
tty carries exactly one process group and that group is running the user's build;
- a child that drops the controlling terminal (`ioctl(TIOCNOTTY)` without `setsid`)
keeps the pgid, reports `tpgid == -1`, and never appears in `ps -t <tty>`;
- a double-forked grandchild keeps the pgid and tty but reparents to pid 1, so the
`ppid` walk cannot reach it and the named-process backstop never fires.
`shellOwnsEveryTtyProcessGroup` now also requires the shell's own process group to
hold no other member anywhere in the table, indexed in the same single pass. A
pids-per-tty set would catch the first and third but not the second, which is why
the count is pgid-wide rather than tty-scoped. The wire field keeps its tty-shaped
name: the value only ever became stricter, so an old client skips more, never less.
Second, unrelated-in-mechanism but same file family: `foregroundSkipReason` summed
`capturedAgeMs + evidenceAgeSinceListingMs` without validating either. A non-numeric
`capturedAgeMs` makes the sum `NaN`, and `NaN > 5000` is false, so a malformed record
PASSED the freshness gate and proceeded toward the stop — the one place in the file
that defaulted toward kill. Nothing validated it on this path
(`mapSshPtyProcessList` checks the ownership fields and spreads the rest through;
`PtyProcessListAdmission` is not on the sweep path). It now runs
`isForegroundProcessEvidence` and fails closed.
Verified on real Linux, not only in mocks: a container drives `bash -i` on a real
pty, builds each construction, runs the real publisher and planner, and then calls
the real `forceKillPosixPtyProcessGroups`. Before, all three published
`shellOwnsEveryTtyProcessGroup: true`, planned SWEEP, and the planted pid was gone
after the signal. After, all three skip and survive, and an idle shell is still
reclaimed.
Residuals are written down at the predicate and in ssh-execution-boundary.md: the
capture is a snapshot (bounded by the evidence-age budget, not removed), and a
process the host's own `ps` cannot enumerate stays unobservable while `killpg`
still reaches it.