fix: daemon idle reaper checks work bead assignee before killing polecats

[dannomayernotabot]

Summary

• The idle polecat reaper checked the agent bead's hook_bead field to determine if a polecat had active work, but updateAgentHookBead() was made a no-op (declaring work bead assignee as authoritative). This caused the reaper to kill working polecats whose agent bead hook_bead pointed to stale/closed beads from previous swarms.
• Adds hasAssignedOpenWork() fallback: before killing a polecat as "working-no-hook", queries bd list --rig=<rig> --assignee=<polecat> --status=hooked (and in_progress, open) to check the authoritative source. If any assigned open work bead exists, the polecat is protected.
• Validated: 20-minute test with 13 polecats — zero reaper kills (was 4+ before fix).

Context

The sling code and daemon reaper disagree about source of truth:

• sling_helpers.go:559: updateAgentHookBead is a no-op, declares "work bead assignee is authoritative"
• daemon.go:2299: idle reaper reads agent bead hook_bead to decide whether to kill

When polecats are reused (same name, new work), the stale hook_bead on the agent bead points to a closed bead from a previous dispatch, causing the reaper to kill the polecat after 15 minutes.

Test plan

• Validated live: slung 13 beads to reused polecat names, waited 20 min past 15-min reaper threshold, zero reaper kills
• Before fix: daemon log showed Reaping idle polecat ... (state=working-no-hook) at 15 min
• After fix: daemon reaper log completely empty
• Build passes (go build ./...)

🤖 Generated with Claude Code

[codecov-commenter]

❌ 1 Tests Failed:

Tests completed	Failed	Passed	Skipped
9395	1	9394	48

View the top 1 failed test(s) by shortest run time

github.com/steveyegge/gastown/internal/daemon::TestReapIdlePolecat_ReapsIdleNoHook

Stack Traces | 0s run time

=== RUN   TestReapIdlePolecat_ReapsIdleNoHook
    polecat_health_test.go:492: expected idle polecat with no agent to be reaped, got: ""
    polecat_health_test.go:495: expected working-no-hook reason, got: ""
--- FAIL: TestReapIdlePolecat_ReapsIdleNoHook (0.00s)

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