fix(l1): resolve PR #193 backend review findings (1,4,5,6,7,8,9,10)

Server-assigns a uuid4 id to every AI-generated node (Finding 1 showstopper:
nodes had no id but the advance protocol keys on node_id, so ai_build walks
never advanced past question 1). Replaces the hidden {"node_type":"meta"}
walked_path convention with real category/problem_text/pending_node columns on
l1_walk_sessions (migration 61dda4f615c6) — fixes junk proposals + off-by-one
depth cap (Findings 8,9), and pending_node replays the served node on re-mount
(no duplicate paid LLM call). Intake honors explicit flow_id and adhoc=True
(Findings 4,5); flow_proposals.l1_session_id FK -> CASCADE (Finding 6 time
bomb); L1 category GET is owner+admin like PATCH and require_account_owner_or_admin
delegates to User.can_manage_account (Finding 7); escalate falls back to default
recipients + filters deleted_at + warns when empty (Finding 10). Cleanups: dead
ticket_ref removed, IntakeResponse per-outcome validator, unused acknowledged
dropped, escalations partial index, restored a deleted audit assertion.

Full Phase 2A backend set: 110 passed / 0 failed.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/app/api/endpoints/l1.py

@@ -35,6 +35,8 @@ def _to_response(session: L1WalkSession) -> WalkSessionResponse:
     return WalkSessionResponse(
         id=session.id,
         session_kind=session.session_kind,
+        category=session.category,
+        problem_text=session.problem_text,
         flow_id=session.flow_id,
         flow_proposal_id=session.flow_proposal_id,
         current_node_id=session.current_node_id,
@@ -68,6 +70,17 @@ async def _get_session_or_404(
     return session
 
 
+async def _create_intake_ticket(db: AsyncSession, payload: IntakeRequest, user: User):
+    return await internal_ticket_service.create_ticket(
+        db,
+        account_id=user.account_id,
+        created_by_user_id=user.id,
+        problem_statement=payload.problem_statement,
+        customer_name=payload.customer_name,
+        customer_contact=payload.customer_contact,
+    )
+
+
 @router.post("/intake", response_model=IntakeResponse)
 async def intake(
     payload: IntakeRequest,
@@ -76,18 +89,49 @@ async def intake(
 ):
     """L1 intake (Phase 2A): match a published flow, else gate + build.
 
-    Runs the match_or_build orchestrator. Outcomes:
+    Two explicit shortcuts run before the matcher (the client already knows what
+    it wants, so re-running the embedding + pgvector + keyword pipeline would be
+    wasteful and — for flow_id — can't reliably re-derive the same flow):
+    - flow_id set  → start that published flow directly (suggest card's "Use this flow").
+    - adhoc=True   → start a free-form ad-hoc walk (out_of_scope prompt's fallback).
+
+    Otherwise match_or_build dispatches:
     - matched  → create ticket + flow session, walk the published flow.
-    - build    → create ticket + ai_build session (category persisted as a hidden
-                 meta entry on walked_path for /next-node), walk an AI-built tree.
+    - build    → create ticket + ai_build session (category + problem_text stored
+                 on the session for /next-node), walk an AI-built tree.
     - suggest  → near-miss prompt; no session created.
     - out_of_scope → category disabled/unknown; no session created.
     """
+    # Explicit flow_id: bypass the matcher, walk the flow the client already holds.
+    if payload.flow_id is not None:
+        ticket = await _create_intake_ticket(db, payload, user)
+        session = await l1_session_service.start_flow_session(
+            db, account_id=user.account_id, user=user, flow_id=payload.flow_id,
+            ticket_id=str(ticket.id), ticket_kind="internal",
+        )
+        await db.commit()
+        return IntakeResponse(
+            outcome="matched", session_id=session.id, session_kind=session.session_kind,
+            ticket_id=str(ticket.id), ticket_kind="internal", flow_id=payload.flow_id,
+        )
+
+    # Explicit ad-hoc walk: the out_of_scope fallback ("Walk it ad-hoc").
+    if payload.adhoc:
+        ticket = await _create_intake_ticket(db, payload, user)
+        session = await l1_session_service.start_adhoc_session(
+            db, account_id=user.account_id, user=user,
+            ticket_id=str(ticket.id), ticket_kind="internal",
+        )
+        await db.commit()
+        return IntakeResponse(
+            outcome="adhoc", session_id=session.id, session_kind=session.session_kind,
+            ticket_id=str(ticket.id), ticket_kind="internal",
+        )
+
     result = await match_or_build.match_or_build(
         user.account_id,
         payload.problem_statement,
         None,
-        ticket_ref="",
         db=db,
         force_build=payload.force_build,
     )
@@ -102,14 +146,7 @@ async def intake(
         )
 
     # matched OR build → create a ticket and a session
-    ticket = await internal_ticket_service.create_ticket(
-        db,
-        account_id=user.account_id,
-        created_by_user_id=user.id,
-        problem_statement=payload.problem_statement,
-        customer_name=payload.customer_name,
-        customer_contact=payload.customer_contact,
-    )
+    ticket = await _create_intake_ticket(db, payload, user)
     if outcome == "matched":
         session = await l1_session_service.start_flow_session(
             db,
@@ -126,13 +163,9 @@ async def intake(
             user=user,
             ticket_id=str(ticket.id),
             ticket_kind="internal",
+            category=result.get("category", "unknown"),
+            problem_text=payload.problem_statement,
         )
-        # Persist the classified category as a hidden meta entry so /next-node
-        # can recover it (no dedicated column; ai_tree_builder skips meta entries).
-        session.walked_path = [
-            {"node_type": "meta", "category": result.get("category", "unknown")}
-        ]
-        await db.flush()
 
     await db.commit()
     return IntakeResponse(
@@ -293,27 +326,18 @@ async def next_node(
 ):
     """Record the answer/ack on the current node, then generate the next node.
 
-    problem_text comes from the linked internal ticket; category from the hidden
-    meta entry seeded at intake (ai_tree_builder skips meta entries). node_text is
-    the rendered text of the node being answered (the client holds it) so the
-    walked path and the captured tree stay legible.
+    problem_text + category are read straight off the session (stored at intake) —
+    no ticket re-fetch, no walked_path scan. node_text is the rendered text of the
+    node being answered (the client holds it) so the walked path and the captured
+    tree stay legible.
     """
     session = await _get_session_or_404(db, session_id, user)
-    ticket = await internal_ticket_service.get_ticket(
-        db, ticket_id=UUID(session.ticket_id)
-    )
-    problem_text = ticket.problem_statement if ticket else ""
-    category = next(
-        (s.get("category") for s in (session.walked_path or [])
-         if s.get("node_type") == "meta"),
-        "unknown",
-    )
     try:
         node = await l1_session_service.advance_ai_build(
             db,
             session_id=session_id,
-            problem_text=problem_text,
-            category=category or "unknown",
+            problem_text=session.problem_text or "",
+            category=session.category or "unknown",
             node_id=payload.node_id,
             node_text=payload.node_text,
             answer=payload.answer,