feat: automate stow on session re-emits and heartbeats

[bingb0t5]

Intent

Implement automatic /stow so the captain does not have to type it.

Two triggers, no new daemon, watcher, or second cascade:
(1) On session-start compact/clear re-emit, prepend a STOW DUE instruction to the digest when state/.last-stow-attempt is missing or older than FM_AUTO_STOW_INTERVAL_SECS (default ~24h); stay silent when current or when the session could not verify fleet-lock ownership.
(2) On heartbeat wake handling (AGENTS.md section 8 rule 4), add one staleness-gated /stow instruction using that same larger interval so a pass runs at most once per interval rather than on every heartbeat wake.

Touch state/.last-stow only at the end of a reset-safe /stow pass. Touch state/.last-stow-attempt at the end of every /stow pass, reset-safe or not, so a sticky exception still throttles automatic retriggering. Away-mode heartbeats stay bash-only.

Executable tests cover the digest line's staleness gate by exercising fm-session-start.sh's real output, never by grepping source.

Accepted decision C: skip wiring heartbeat /stow into the Pi supervision branch; do not edit fm-branch-prompt.sh. Document that gap and file follow-up #2944. Compact/clear re-emit remains the automatic path on default Pi.

Also applied remaining review auto-fixes: promote the marker-touch instructions out of the cascade heading so secondmate homes still throttle, and pin the stale-marker age assertion to a 9xxxx band instead of the prefix 900.

This PR targets https://github.com/bingb0t5/firstmate; the captain cannot merge upstream themselves.

What Changed

• Add a staleness-gated STOW DUE instruction to lock-owning compact/clear session re-emits, with a configurable 24-hour default interval.
• Run automatic /stow during eligible heartbeat handling and track both attempted and reset-safe passes so unresolved exceptions remain throttled.
• Document automatic stow behavior, marker semantics, and the deferred Pi supervision-branch integration tracked by issue Wire heartbeat automatic /stow into the Pi supervision branch #2944.

Risk Assessment

✅ Low: The change is well-bounded, satisfies the automatic stow intent and prior fixes, and introduces no substantiated merge-blocking source risk.

Testing

The focused session-start suite passed, including lock ownership, default and custom staleness intervals, attempt-marker throttling, read-only silence, and ordinary-startup exclusion; a reviewer-visible CLI transcript demonstrates the real missing, fresh, and stale marker behavior. No screenshot was captured because this is a CLI digest change with no rendered UI.

Evidence: Automatic stow session-start transcript

Source: Automatic stow session-start transcript

Missing and stale markers emit STOW DUE before BOOTSTRAP; a fresh marker emits zero STOW DUE lines.

SCENARIO 1 - missing attempt marker, lock-owning clear re-emit
STOW DUE: no recorded /stow pass (source=clear); run /stow before other work.
BOOTSTRAP

SCENARIO 2 - fresh attempt marker, same re-emit
STOW DUE lines: 0

SCENARIO 3 - stale attempt marker (90000 seconds), default interval
STOW DUE: last /stow pass was 90000s ago (over the 86400s interval, source=compact); run /stow before other work.

Pipeline

Updates from git push no-mistakes

✅ **intent** - passed

✅ No issues found.

✅ **Rebase** - passed

✅ No issues found.

🔧 **Review** - 1 issue found → auto-fixed ✅

• ⚠️ bin/fm-session-start.sh:364 - FM_AUTO_STOW_INTERVAL_SECS accepts any nonzero digit string, but [ cannot compare values outside the shell's integer range. For example, with a stale marker and FM_AUTO_STOW_INTERVAL_SECS=999999999999999999999, the comparison errors and || return 0 silently suppresses STOW DUE. Validate the configured value against a supported upper bound before using it.

🔧 Fix: Cap automatic stow interval safely
✅ Re-checked - no issues remain.

✅ **Test** - passed

✅ No issues found.

• bash tests/fm-session-start.test.sh
• Real bin/fm-session-start.sh --reemit checks for missing, fresh, and 90000-second-old state/.last-stow-attempt markers using the session-start test harness; transcript captured with tee
• git status --short after testing to confirm no transient worktree artifacts remained

✅ **Document** - passed

✅ No issues found.

🔧 **Lint** - 1 issue found → auto-fixed ✅

• ⚠️ linter found issues (exit code 1)

🔧 Fix: Fix numeric stow interval lint comparison
✅ Re-checked - no issues remain.

✅ **Push** - passed

✅ No issues found.

[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

_{Reviews (4): Last reviewed commit: "no-mistakes: apply CI fixes" | Re-trigger Greptile}