- Stale hashed control sockets under /tmp/meridian-<uid>/ after hard-killed
  runners: spawn-dir GC doesn't know the external endpoint. Tracked in
  GitHub issue #445 (derive control_socket_path during reaper
  reconciliation / spawn-dir pruning and unlink for terminal spawns).
- `completion_coordinator.py`, `descendant_evidence.py`, and spawn admission:
  characterize the remaining race between a qualifying final descendant snapshot and
  terminal lifecycle publication. Decide whether parent-closing admission needs a
  protocol of its own; request-sequenced refresh narrows stale evidence but is not an
  atomic admission barrier. Do not add a ledger, counter, or notification bus without
  establishing that stronger requirement.
- `pi_drain.py`, `pi_quiescence.py`, and Pi's native event contract: before supporting
  arbitrary third-party branch-summary work inside spawned sessions, establish a
  paired lifecycle signal and qualify it with a native replay. Queue updates and
  summarization-retry telemetry cannot establish either busy or idle on their own.
  Current qualification covers agent runs and ordinary compaction, not arbitrary
  branch-summary/session-tree operations; do not restore an unpaired activity latch.
