Scheduler does not dispatch eligible assigned todo tasks to online runner

[saltbo]

Summary

Agent Kanban v1.15.0 does not dispatch eligible assigned todo tasks to an online machine runner. The runner remains connected and reports no assignments.

Environment

• ak: 1.15.0 (also reproduced on 1.4.0 before upgrade)
• macOS machine runner
• runner: online, relay connected, runtimes codex + copilot
• board: 2ih1vz3s
• repository: nvea6xi8

Reproduction A: ordinary eligible task

Task ps7pxx7gby8s:

• status: todo
• assigned agent e0a1ce35687e48ef: schedulable, runtime codex, 0 in progress
• only dependency 54g78mrg2rdb: done
• active_session_id: null
• scheduled_at manually set to a past timestamp (2026-07-29T14:50:00Z) through ak apply
• not blocked

ak wait task ps7pxx7gby8s --until in_progress timed out after 10 minutes on 1.4.0 and again after 5 minutes on 1.15.0.

Reproduction B: merged task released to todo

Task l4ckb379958o:

• status: todo
• linked PR saltbo/zpan#537 is merged
• assigned agent b0abe6cd7aeba133: schedulable, 0 in progress
• only dependency is done
• retains a stale active_session_id from a runner-cancelled session

It likewise received no assignment after restart/upgrade.

Runner evidence

runner ready; waiting for work assignments
runner relay channel connected

No assignment or work-item event follows. Heartbeats remain current.

Expected

An eligible assigned todo task is dispatched to its schedulable agent, or the API exposes a reason it is not eligible. Setting a past scheduled_at should not leave it permanently dormant.

Actual

Both tasks remain todo indefinitely while the runner and agents are schedulable. Updating dependencies and scheduled_at produced task update events but did not trigger dispatch.

Notes

Issue #194 separately covers leader recovery when a merged PR task is stuck before in_review. This issue is about scheduler eligibility/dispatch and the absence of diagnostic state.