Implements the remaining observers from RFC #58548 (@thebizfixer),
accepted as the design basis in the #64231 batch disposition:
- on_kanban_worker_spawned: fires in the dispatch loop after spawn_fn
returns and the worker PID is durably persisted (the RFC timing
contract), in both the ready and review lanes.
- on_kanban_worker_exited: tick-derived from detect_crashed_workers;
fires after every reclaim/accounting txn has committed, carrying
exit_kind / exit_code / outcome / retry_status.
- on_kanban_worker_stale_claim: fires when release_stale_claims
reclaims a TTL-expired claim; live-PID claim extensions and deferred
reclaims stay silent.
- on_kanban_task_updated: task-mutation boundary observer carrying
changed_fields (field names only); fired by assign_task,
set_model_override, and set_reasoning_effort, and by the dashboard
plugin API's direct-SQL priority/title/body editors (single and
bulk) through the new kanban_db.notify_task_updated seam.
- on_kanban_dispatch_tick: re-port of PR #56066 (@laboratoiresonore),
renamed per the taxonomy and fired strictly AFTER _dispatch_tick_lock
is released; the sweeper found the original fired inside the lock,
where a slow subscriber could extend the single-writer critical
section and stall a sibling dispatcher.
All five are observer-only (return values ignored), fire after the
relevant write txn commits, and short-circuit on has_hook() so nothing
is built when no consumer registers; every fire site is fully
best-effort so a broken plugin can never break dispatch or a task
mutation. No config surface added. Existing plugins and hook payloads
are untouched.
Mutation-boundary scope: every user-facing task-FIELD editor fires
(assignee, priority, title, body, model/provider override, reasoning
effort). Deliberately not wired: status transitions (they belong to
the lifecycle hook family), dispatcher bookkeeping columns
(worker_pid, workspace_path, claim columns — surfaced through the
worker hooks instead), link/comment/attachment tables (not task-row
writes), and the dispatcher's default-assignee auto-assign (already
surfaced via DispatchResult.auto_assigned_default in the tick
payload). notify_task_updated is the seam for wiring further paths.
Docs: new rows plus a detail section in the shipped plugin-hook catalog.
Tests: 30 new (9 worker lifecycle, 8 dispatch tick, 8 task updated,
5 dashboard mutation boundary), including a lock-probe contract test
that fails if the tick hook ever fires inside the dispatch lock.
Refs: RFC #58548, #64231 batch disposition, folds #56066.
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