fix(core): a child never leaves its parent waiting silently

[devin-ai-integration]

Summary

Fixes #947, and the sibling gaps around it: every way a child can stop running now produces exactly one message to its parent. Before, terminal notices covered crashed/failed/stopped-on-turn-limit only, so a completed child had a single channel — the report agent_finish sends — and report_to_parent=False, a stop driven by another agent, or a loop exiting after the status was already settled all left the parent waiting out its full wait_for_agents timeout on a message nobody would send.

• _TERMINAL_NOTICE gains a completed entry, and agent_finish sends it whenever it skips the report:

  parent_notified = False
  if report_to_parent and await coordinator.claim_parent_notice(me):
      ...send report...; parent_notified = True
  await coordinator.set_status(me, "completed")
  if not parent_notified:
      await notify_parent_on_terminal(coordinator, me, "completed")

• _child_loop gets a finally backstop (_notify_parent_on_exit) that notifies on whatever terminal status the child exited with, so no exit path is silent. Skipped during shutdown; cancellation propagates as before.
• stop_agent notifies the stopped agents' parents, except the stopper itself (which already knows) — this is the grandchild case: root stops a grandchild, and the middle agent waiting on it otherwise never hears. cancel_descendants_graceful now returns the stopped ids so the tool can address them. The stopped notice no longer claims "hit its turn limit", since it now also covers explicit stops.
• Dedupe lives in the coordinator: claim_parent_notice(agent_id) hands out one notice per running stint, and returning to running clears the claim so a revived child can report again. The report and the terminal notice claim the same slot, so a parent never receives both.
• notify_parent_on_terminal is now public (called from the tools layer).

Tests: test_terminal_child_wakes_parked_parent is parametrized with completed, plus coverage for a report-less agent_finish waking a parked parent, a delivered report suppressing the backstop notice, and both stop_agent cases.

Note: tests/test_execution.py::test_finish_scan_bypasses_active_agent_guard_after_reserve fails in a full-suite run on main as well (a ReportState.run_record ordering issue) — unrelated to this change.

Link to Devin session: https://app.devin.ai/sessions/2f28685f6b0e4bcfbd407373c9580516
Requested by: @0xallam

[devin-ai-integration]

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[greptile-apps]

Greptile Summary

The PR ensures that child-agent terminal paths notify their parents once instead of leaving them waiting for a report that will never arrive.

• Adds coordinator-level deduplication shared by completion reports and terminal notices.
• Adds completed and explicit-stop notifications plus a child-loop exit backstop.
• Propagates stopped-agent identifiers so non-stopping parents can be notified.
• Expands lifecycle tests for report-less completion, deduplication, and nested-agent stopping.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains within the eligible follow-up-review scope.

Important Files Changed

Filename	Overview
strix/core/agents.py	Adds per-running-stint parent-notification claims and returns stopped descendant identifiers for downstream notification.
strix/core/execution.py	Extends terminal notices to completed children and adds an exit-time notification backstop around detached child loops.
strix/tools/agents_graph/tools.py	Coordinates completion-report deduplication and notifies parents affected by third-party subtree stops.
tests/test_execution.py	Adds regression coverage for completed-child wakeups, report suppression, report-less completion, and nested stop notifications.

_{Reviews (2): Last reviewed commit: "fix(tools): tell a waiting parent when s..." | Re-trigger Greptile}

[0xallam]

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