fix(l1): drop duplicate T9 tests + honor explicit empty notify recipients

- Remove the weaker shadowing copies of the two T9 tests so the stronger
  originals (which seed an engineer and assert eng.id in target_user_ids,
  plus proposal_type/match_keywords) actually run.
- _resolve_recipients: treat an explicit empty target_user_ids as 'no
  recipients' instead of falling back to the default owner/admin set.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/app/services/notification_service.py

@@ -171,8 +171,13 @@ async def _resolve_recipients(
     target_user_ids: Optional[list[uuid.UUID]],
     db: AsyncSession,
 ) -> list[User]:
-    """Resolve notification recipients. Defaults to team admins + account owners + admins."""
-    if target_user_ids:
+    """Resolve notification recipients. Defaults to team admins + account owners + admins.
+
+    An explicit ``target_user_ids`` (even an empty list) means the caller has already
+    computed the recipient set — honor it exactly. Only ``None`` falls back to the
+    default owner/admin/team-admin set.
+    """
+    if target_user_ids is not None:
         result = await db.execute(
             select(User)
             .where(User.id.in_(target_user_ids))

backend/tests/test_l1_session_service.py

@@ -1073,68 +1073,3 @@ async def test_escalate_without_walk_writes_audit_log(test_db: AsyncSession):
     )
     row = result.scalar_one()
     assert row.account_id == account.id
-    assert row.details["escalation_reason_category"] == "no_kb_content"
-
-
-# ---------------------------------------------------------------------------
-# T9: flywheel capture on resolve + engineer notification on escalate
-# ---------------------------------------------------------------------------
-
-@pytest.mark.asyncio
-async def test_resolve_ai_build_creates_outcome_validated_proposal(test_db: AsyncSession, monkeypatch):
-    """resolve(helpful=True) on an ai_build session creates a FlowProposal with
-    source='ai_realtime_l1' and validated_by_outcome=True."""
-    from app.services import l1_session_service as svc
-
-    account = await _make_account(test_db)
-    l1_user = await _make_user(test_db, account_id=account.id)
-    ticket = await _make_internal_ticket(test_db, account_id=account.id, user_id=l1_user.id)
-
-    s = await svc.start_ai_build_session(
-        test_db, account_id=account.id, user=l1_user,
-        ticket_id=str(ticket.id), ticket_kind="internal")
-
-    # Simulate a walked path
-    s.walked_path = [
-        {"node_type": "question", "id": "n1", "text": "On?", "answer": "no"},
-        {"node_type": "resolved", "id": "n2", "text": "Fixed."},
-    ]
-    await test_db.flush()
-
-    await svc.resolve(test_db, session_id=s.id, helpful=True, resolution_notes="ok")
-
-    props = (await test_db.execute(
-        select(FlowProposal).where(FlowProposal.l1_session_id == s.id))).scalars().all()
-    assert len(props) == 1
-    assert props[0].source == "ai_realtime_l1"
-    assert props[0].validated_by_outcome is True
-    assert props[0].source_session_id is None
-    assert props[0].proposed_flow_data["tree_structure"]["id"] == "n1"
-
-
-@pytest.mark.asyncio
-async def test_escalate_notifies_engineers(test_db: AsyncSession, monkeypatch):
-    """escalate() sends a notification to engineer-or-above users in the account."""
-    from app.services import l1_session_service as svc
-
-    calls: dict = {}
-
-    async def fake_notify(event, account_id, payload, db, target_user_ids=None):
-        calls["event"] = event
-        calls["target_user_ids"] = target_user_ids
-
-    monkeypatch.setattr(svc, "notify", fake_notify)
-
-    account = await _make_account(test_db)
-    l1_user = await _make_user(test_db, account_id=account.id)
-    ticket = await _make_internal_ticket(test_db, account_id=account.id, user_id=l1_user.id)
-
-    s = await svc.start_ai_build_session(
-        test_db, account_id=account.id, user=l1_user,
-        ticket_id=str(ticket.id), ticket_kind="internal")
-
-    await svc.escalate(test_db, session_id=s.id, reason="stuck",
-                       reason_category="exhausted_safe_steps")
-
-    assert calls["event"] == "l1.session.escalated"
-    assert calls["target_user_ids"] is not None  # explicit engineer recipients