fix(lifecycle): stop cell-PM redirect clobbering review handoffs; cascade dependency prune on delete/cancel

Two live bugs the CEO hit daily, both in TaskService:

1. awaiting_qa / awaiting_documentation tasks were assigned to the cell
PM (be-pm) and deadlocked until manually reassigned. _resolve_cell_pm_redirect
forces every cell-PM-owned task type (documentation/design/research/planning/
administrative) onto the cell PM on every reassign(). The gateway hands off
to QA (i_am_done) and to the documenter (pass_review) via reassign(), so the
redirect clobbered the rightful reviewer — who has no claim right on those
states per CLAIM_RULES. The redirect is for delegation/escalation ownership
routing, not for clobbering a review handoff. Gate it on
_REVIEW_HANDOFF_STATUSES (awaiting_qa / awaiting_documentation /
awaiting_pr_review); awaiting_pm_review is deliberately excluded (the cell
PM IS the owner there, so the redirect still fires).

2. Deleting or cancelling a task left a dependent BLOCKED on it stuck
forever — the CEO caught a good-to-go task held by a stale dependency on a
deleted task. delete() and cancel() never called _unblock_dependents (the
edge-prune only the complete()/ceo_approve paths ran), so a BLOCKED
dependent was never auto-revived. (A PENDING dependent's claim was not
blocked — unmet_dependency_ids treats a missing row as "met" — but a
BLOCKED dependent is past the gate and only _unblock_dependents revives it.)
Both paths now loop _unblock_dependents over the root and every descendant;
idempotent, and a deleted id in completed_dependency_ids is a dead-end node
in the sequence graph so it cannot false-block.

Tests: 3 unit (review-handoff preserved for QA/doc/PR-reviewer; PM-review and
CLAIMED redirects still fire) + 3 integration (delete/cancel revive a BLOCKED
dependent; delete prunes a PENDING dependent).

tests/unit/services/test_task_assignment_invariants.py

@@ -311,3 +311,122 @@ def test_create_does_not_redirect_misassigned_cell_planning_child() -> None:
     assert not hasattr(svc, "_redirect_cell_team_pm_task"), (
         "create-path redirect was re-added; remove it (see audit Gap 1)."
     )
+
+
+# ---------------------------------------------------------------------------
+# Regression — review-pipeline handoffs must NOT be redirected to the cell PM
+#
+# A cell-PM-owned task type (documentation / design / research / planning /
+# administrative) that enters a review state (awaiting_qa / awaiting_documentation
+# / awaiting_pr_review) is mid-handoff to a non-PM claimant (QA / documenter /
+# PR reviewer per CLAIM_RULES). The cell-PM ownership redirect is for
+# delegation/escalation routing, not for clobbering the review claimant —
+# redirecting here lands the task on the cell PM, who has no claim right on
+# these states, so it deadlocks until a human manually reassigns.
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.parametrize(
+    "status",
+    [
+        TaskStatus.AWAITING_QA,
+        TaskStatus.AWAITING_DOCUMENTATION,
+        TaskStatus.AWAITING_PR_REVIEW,
+    ],
+)
+@pytest.mark.parametrize(
+    "task_type",
+    [TaskType.DOCUMENTATION, TaskType.DESIGN, TaskType.RESEARCH],
+)
+@pytest.mark.asyncio
+async def test_reassign_keeps_review_handoff_for_cell_pm_owned_child(
+    status: TaskStatus, task_type: TaskType
+) -> None:
+    """The QA / documenter / PR-reviewer handoff into a review state keeps
+    the requested reviewer — the cell-PM redirect does not fire there."""
+    svc = _service()
+    reviewer_id = uuid4()
+    task = _task(
+        team=Team.BACKEND,
+        task_type=task_type,
+        assigned_to=None,
+        status=status,
+    )
+    _bind(svc, "get", AsyncMock(return_value=task))
+    _bind(svc, "_is_board_advisory_agent", AsyncMock(return_value=False))
+    # cell_pm_for_team must NOT be consulted when the status gate fires —
+    # if it is, the test fails because the AsyncMock has no return_value.
+    _bind(
+        svc,
+        "cell_pm_for_team",
+        AsyncMock(
+            side_effect=AssertionError(
+                "cell_pm_for_team must not run for a review-handoff state"
+            )
+        ),
+    )
+
+    result = await svc.reassign(task.id, reviewer_id)
+
+    assert result is task
+    assert task.assigned_to == reviewer_id
+    assert task.claimed_by == reviewer_id
+    assert "[ASSIGNMENT REDIRECTED]" not in (task.dev_notes or "")
+
+
+@pytest.mark.asyncio
+async def test_reassign_still_redirects_on_awaiting_pm_review() -> None:
+    """AWAITING_PM_REVIEW is NOT a review-handoff state — the cell PM is the
+    rightful owner there, so the redirect still fires. Guards against the
+    status gate over-broadening and breaking PM-review ownership."""
+    svc = _service()
+    be_pm_id = uuid4()
+    main_pm_id = uuid4()
+    task = _task(
+        team=Team.BACKEND,
+        task_type=TaskType.PLANNING,
+        assigned_to=main_pm_id,
+        status=TaskStatus.AWAITING_PM_REVIEW,
+    )
+    _bind(svc, "get", AsyncMock(return_value=task))
+    _bind(svc, "_is_board_advisory_agent", AsyncMock(return_value=False))
+    _bind(
+        svc,
+        "cell_pm_for_team",
+        AsyncMock(return_value=MagicMock(id=be_pm_id, slug="be-pm")),
+    )
+
+    result = await svc.reassign(task.id, main_pm_id)
+
+    assert result is task
+    assert task.assigned_to == be_pm_id
+    assert "[ASSIGNMENT REDIRECTED]" in task.dev_notes
+
+
+@pytest.mark.asyncio
+async def test_reassign_still_redirects_on_claimed_planning_child() -> None:
+    """The non-review routing paths (delegation/escalation on PENDING /
+    CLAIMED / NEEDS_REVISION) keep the redirect — the status gate only
+    covers the review-handoff states, not ownership routing."""
+    svc = _service()
+    be_pm_id = uuid4()
+    main_pm_id = uuid4()
+    task = _task(
+        team=Team.BACKEND,
+        task_type=TaskType.PLANNING,
+        assigned_to=main_pm_id,
+        status=TaskStatus.CLAIMED,
+    )
+    _bind(svc, "get", AsyncMock(return_value=task))
+    _bind(svc, "_is_board_advisory_agent", AsyncMock(return_value=False))
+    _bind(
+        svc,
+        "cell_pm_for_team",
+        AsyncMock(return_value=MagicMock(id=be_pm_id, slug="be-pm")),
+    )
+
+    result = await svc.reassign(task.id, main_pm_id)
+
+    assert result is task
+    assert task.assigned_to == be_pm_id
+    assert "[ASSIGNMENT REDIRECTED]" in task.dev_notes