fix(lifecycle): pr_pass hands ownership to the owning PM — closes the passed-PR completion wedge

Removing the awaiting_pm_review re-claim edge (d87e2d9b, the #740
review-loop fix) exposed that the edge was load-bearing: pr_pass
cleared assigned_to/claimed_by to None and the re-claim was the only
way a PM ever re-acquired the task. Since then every assembled task
passing the PR gate wedged: the closure PM's complete rejected with
'not assigned to you', its fallback claim rejected (edge gone), and
its only exit was escalate_up — BLOCKING the task onto main-pm, who
is not the assignee either and burned spawns doing nothing. Live:
PR #741's task (7 ownership rejections, escalated 13:59Z), plus two
more tasks with 25 and 2 rejections in the same shape.

pr_pass now resolves the owning PM via _revision_pm_for_task and
assigns it, exactly as pr_fail always did — one chokepoint covering
cell (submit_up) and root (submit_root) tasks. mark_pr_created's
ready_for_pm branch (leaf docs-path, PR-arrives-second) had the same
clear-to-None wedge and now resolves via _resolve_pm_for_review like
its docs-first sibling. No claim edge is reintroduced; the #740
parity test is untouched.

Recovery for already-wedged tasks needs no DB surgery: new idempotent
TaskService.assign_review_pm + POST /tasks/{id}/assign-review-pm
(ASSIGN-gated, explicit commit) corrects an unassigned OR mis-assigned
awaiting_pm_review task to its owning PM; _dispatch_pm_review_work
ensures assignment before every spawn (cheap pre-check skips the
round-trip when the fetched assigned_to already matches), replacing
the dead _claim_task_for_agent call whose lifecycle claim the removed
edge now always rejects; _maybe_spawn_pm_closure routes through
_closure_review_pm, which keeps the team-resolved PM whenever the
assign route fails so a transient error can never spawn a stale
assignee.

Gate: 15506 passed, 459 skipped; xenon/ruff/mypy/vulture/bandit/
pip-audit/deptry/import-linter/foundation-check green.

tests/integration/test_lifecycle_real_db.py

@@ -899,10 +899,22 @@ async def test_pr_review_gate_pass_path(
     assert reviewer_row.status == AgentStatus.ACTIVE
     assert reviewer_row.current_task_id == task.id
 
+    # Resolved via the same team-based query pr_pass itself uses (rather than
+    # assumed to be this fixture's own cell_pm_agent) — the shared/cumulative
+    # integration DB may carry other BACKEND/CELL_PM agents from earlier
+    # tests, and _agent_with_role_and_team has no ordering guarantee.
+    expected_pm = await svc.cell_pm_for_team(Team.BACKEND)
+    assert expected_pm is not None
+
     passed = await svc.pr_pass(reviewer_id, task.id, notes="integration verified")
     assert passed is not None
     assert str(passed.status) == Status.AWAITING_PM_REVIEW.value
-    assert passed.assigned_to is None  # cleared so the PM-closure dispatch routes
+    # Hands off to the owning cell PM (team-resolved) rather than clearing —
+    # AWAITING_PM_REVIEW has no claim() edge, so an unassigned task here has
+    # no way back to a PM.
+    assert passed.assigned_to == expected_pm.id
+    assert passed.claimed_by == expected_pm.id
+    assert passed.active_claimant_id is None
     # pr_pass releases the reviewer's fleet marker too.
     reviewer_row = await db_session.get(AgentTable, reviewer_id)
     assert reviewer_row is not None