fix(bin): stop dead harness agents from reporting stale liveness

[SimTet]

What Changed

• bin/fm-crew-state.sh: when a crew has no matching run, consult the recovery-grade fm_backend_agent_state classifier before falling back to busy-hook or status-log state; a confident dead/missing verdict now reports unknown · agent-state instead of trusting a frozen busy read or stale log line from a harness process that has died but whose pane/shell still answers.
• bin/fm-fleet-snapshot.sh: endpoint.agent_alive is now populated for every task with a recorded target (not only secondmates), reusing the same fm_backend_agent_alive classifier; tasks with no recorded target still report not_checked.
• bin/fm-push-transition-lib.sh: the push-transition handler now checks fm_backend_meta_for_window before routing a transition; a pane with no currently recorded task (a torn-down task's former pane, or an endpoint Firstmate never owned) has its transition committed and absorbed instead of being misrouted to the wrong crew.
• Updated docs/architecture.md and docs/herdr-backend.md to describe the new agent-state pre-check ordering and the push-transition retired-pane exemption, and added/extended tests in tests/fm-crew-state.test.sh, tests/fm-supervision-events.test.sh, and tests/fm-bearings-snapshot.test.sh covering these paths.

Risk Assessment

✅ Low: Two well-scoped liveness-detection fixes (crew-state no-run fallback and herdr push-transition retired-pane absorption) reuse existing, single-owner classifiers at the correct shared boundary, preserve byte-identical behavior for every inconclusive verdict, and are backed by regression tests that exercise real function behavior (fake tmux/herdr process trees, real fm_backend_agent_state calls) rather than source-text matching; the author also caught and fixed their own test-fixture fallout from the broadened fm-fleet-snapshot.sh scope in a follow-up commit.

Testing

All five targeted bash test suites relevant to this branch's crew-liveness and retired-pane fixes pass cleanly (133 assertions total across the suites), including every new regression test the branch adds for the crew-exit-probe incident (confirmed-dead vs confirmed-alive vs inconclusive agent-state verdicts, and retired-pane push-edge absorption vs live-pane wake); this is a bash CLI/library codebase with no UI surface, so the CLI test transcripts are the appropriate evidence and are captured below rather than as visual artifacts.

Evidence: fm-crew-state.test.sh — new confirmed-dead-agent regression assertions

ok - a confirmed-dead agent overrides a frozen working status log
ok - a confirmed-dead agent overrides a frozen busy hook record
ok - an explicitly confirmed-alive agent still reports working from its busy record
ok - ambiguous and unreadable agent-state verdicts fall through byte-identical to baseline
ok - a backend with no recovery-grade classifier falls through unchanged
all fm-crew-state tests passed

Evidence: fm-supervision-events.test.sh — retired-pane absorption vs live-pane wake

ok - handle_push_transition: a pane with no recorded task (torn down, or never one) is absorbed - never a wake
ok - handle_push_transition: the identical pane still wakes once it is a recorded live task (fix is scoped to unrecorded panes)
# fm-supervision-events.test.sh: all assertions passed

Pipeline

Updates from git push no-mistakes

⏭️ **intent** - skipped

✅ No issues found.

✅ **Rebase** - passed

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✅ **Review** - passed

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✅ **Test** - passed

✅ No issues found.

• ./tests/fm-crew-state.test.sh (54/54 pass, incl. 5 new: confirmed-dead agent overrides stale status log / frozen busy hook, confirmed-alive agent still reports working, ambiguous+unreadable verdicts fall through byte-identical to baseline, unverified backend falls through unchanged)
• ./tests/fm-supervision-events.test.sh (9/9 pass, incl. 2 new: a pane with no recorded task is absorbed - never wakes the supervisor - while the identical pane on a live recorded task still wakes)
• ./tests/fm-bearings-snapshot.test.sh (40/40 pass; exercises fm-fleet-snapshot.sh's now-broadened agent_alive check end-to-end and validates the dfabbeb fixture fallback fix for list-windows)
• ./tests/fm-secondmate-liveness.test.sh (15/15 pass; exercises the underlying fm_backend_agent_state/fm_backend_agent_alive classifier reused by this branch's callers, confirming the classifier itself is untouched)
• ./tests/fm-fleet-snapshot-view.test.sh (15/15 pass; confirms secondmate agent-liveness rendering is unaffected)

✅ **Document** - passed

✅ No issues found.

✅ **Lint** - passed

✅ No issues found.

✅ **Push** - passed

✅ No issues found.