fix(bin): account for every registered secondmate in liveness sweep

[keenvc]

Problem

The session-start secondmate liveness sweep walked only state/<id>.meta records filtered to kind=secondmate. That made two classes of registered secondmate invisible to the sweep meant to guarantee they are running:

• A secondmate registered in data/secondmates.md with no state/<id>.meta record was never enumerated at all.
• A secondmate with a record but no recorded backend endpoint (window= empty) was silently skipped by the [ -n "$window" ] || return 0 guard.

Both are recovery-grade failures. Because the sweep reports healthy when it declines, the outage was invisible until a new secondmate happened to be requested on a project that already had two.

Fix

bin/fm-bootstrap.sh secondmate_liveness_sweep now enumerates the union of:

• registered ids from data/secondmates.md (the durable "which secondmates exist" authority), and
• kind=secondmate state/<id>.meta records,

deduplicated so a running registered secondmate is probed exactly once. A registered id with no record, or with a record that has no endpoint, is relaunched from its registry entry and persistent home via the existing bin/fm-spawn.sh <id> --secondmate recovery path. A relaunch that fails is reported as an explicit named gap:

SECONDMATE_LIVENESS: secondmate <id>: gap: <cause> and relaunch from registry failed: <error>

A meta record whose kind is not secondmate is not treated as the secondmate's endpoint, so a colliding task record cannot be probed.

Behavior preserved

• Recovery still only authorizes dead / missing classifier states; ambiguous, unreadable, unverified-harness, and unreachable-remote targets remain skipped: with their reason.
• Already-live and successfully relaunched secondmates stay silent by default.
• A secondmate's own home still sees a silent no-op (it holds no kind=secondmate meta and registers no secondmates).

Tests

tests/fm-secondmate-liveness.test.sh extended with six cases:

• a registered secondmate with no metadata record is recovered from the registry, not passed over;
• a record with no recorded endpoint is recovered rather than skipped;
• an unrecoverable registered secondmate (relaunch fails) is named as a gap;
• a registered secondmate whose home is not seeded is named as a gap;
• a registered id with a live record is probed once and never relaunched;
• a kind=secondmate record absent from the registry is still accounted for.

All existing cases in the file pass, plus fm-bootstrap, fm-session-start, fm-secondmate-sync, fm-bootstrap-network-parallel, fm-remote-secondmate-lifecycle-e2e, fm-secondmate-lifecycle-e2e, and fm-secondmate-safety. bin/fm-doc-audience-check.sh passes.

Docs

Updated the owned prose in AGENTS.md, docs/configuration.md, .agents/skills/bootstrap-diagnostics/SKILL.md, and .agents/skills/secondmate-provisioning/SKILL.md so the documented contract matches the enforced behavior.