Assistant: persist the chat thread in Postgres

Back MAF's opt-in AG-UI snapshot persistence with a DB store so the
conversation survives page reloads and restarts:

- ChatThreadSnapshot: one upserted row per (scope, thread_id), JSONB
  messages/state/interrupt (migration 794baf50635b)
- PostgresSnapshotStore implements the AGUIThreadSnapshotStore protocol.
  It opens its own sessions (MAF saves during SSE streaming, after the
  request middleware has closed the ContextVar session) and sanitizes on
  save: camelCase toolCalls/toolCallId (the @ag-ui/client Zod schema
  strips snake_case, which would lose cards on replay), drop BFF ctx-*
  context messages, dedupe MAF's re-recorded multi-run turns, and drop
  orphaned tool results
- Endpoint mount gains snapshot_store + a constant scope resolver
  (single-user app; auth already enforced by agent_auth_and_session)
- DELETE /api/v1/chat/thread resets the conversation

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/tests/test_chat_persistence.py

@@ -0,0 +1,131 @@
+"""Chat thread persistence: snapshot store round-trip + clear endpoint."""
+
+import asyncio
+
+from agent_framework_ag_ui import AGUIThreadSnapshot
+from sqlmodel import select
+
+import app.agent.snapshot_store as snapshot_store_module
+from app.agent.snapshot_store import PostgresSnapshotStore
+from app.api.v1.endpoints.chat import clear_thread
+from app.models.models import ChatThreadSnapshot
+
+
+def _store(monkeypatch, engine):
+    # The store opens its own sessions from app.db.engine; point it at the
+    # test engine instead.
+    monkeypatch.setattr(snapshot_store_module, "engine", engine)
+    return PostgresSnapshotStore()
+
+
+def test_save_get_roundtrip_normalizes_and_filters(monkeypatch, engine):
+    store = _store(monkeypatch, engine)
+    snapshot = AGUIThreadSnapshot(
+        messages=[
+            {"id": "u1", "role": "user", "content": "hola"},
+            {
+                "id": "a1",
+                "role": "assistant",
+                "content": "",
+                # MAF emits snake_case; the store must return camelCase so
+                # @ag-ui/client's Zod schema doesn't strip it.
+                "tool_calls": [{"id": "t1", "type": "function"}],
+            },
+            {"id": "t1r", "role": "tool", "content": "ok", "tool_call_id": "t1"},
+            # MAF writes tool_calls: null on plain-text assistant messages —
+            # must not survive as toolCalls: null in the replay.
+            {"id": "a2", "role": "assistant", "content": "done", "tool_calls": None},
+            {"id": "ctx-123", "role": "system", "content": "run context"},
+        ],
+        state={"k": "v"},
+    )
+    asyncio.run(store.save(scope="default", thread_id="main", snapshot=snapshot))
+
+    loaded = asyncio.run(store.get(scope="default", thread_id="main"))
+    assert loaded is not None
+    assert [m["id"] for m in loaded.messages] == ["u1", "a1", "t1r", "a2"]
+    assistant = loaded.messages[1]
+    assert "tool_calls" not in assistant
+    assert assistant["toolCalls"] == [{"id": "t1", "type": "function"}]
+    tool_msg = loaded.messages[2]
+    assert "tool_call_id" not in tool_msg
+    assert tool_msg["toolCallId"] == "t1"
+    text_msg = loaded.messages[3]
+    assert "toolCalls" not in text_msg and "tool_calls" not in text_msg
+    assert loaded.state == {"k": "v"}
+
+
+def test_save_upserts_single_row(monkeypatch, engine, session):
+    store = _store(monkeypatch, engine)
+    for n in range(3):
+        snap = AGUIThreadSnapshot(
+            messages=[{"id": f"u{i}", "role": "user", "content": str(i)} for i in range(n + 1)]
+        )
+        asyncio.run(store.save(scope="default", thread_id="main", snapshot=snap))
+
+    rows = session.exec(select(ChatThreadSnapshot)).all()
+    assert len(rows) == 1
+    assert len(rows[0].messages) == 3
+
+
+def test_get_unknown_thread_returns_none(monkeypatch, engine):
+    store = _store(monkeypatch, engine)
+    assert asyncio.run(store.get(scope="default", thread_id="nope")) is None
+
+
+def test_delete_and_scope_isolation(monkeypatch, engine):
+    store = _store(monkeypatch, engine)
+    snap = AGUIThreadSnapshot(messages=[{"id": "u1", "role": "user", "content": "x"}])
+    asyncio.run(store.save(scope="default", thread_id="main", snapshot=snap))
+
+    assert asyncio.run(store.get(scope="other", thread_id="main")) is None
+    assert asyncio.run(store.delete(scope="default", thread_id="main")) is True
+    assert asyncio.run(store.delete(scope="default", thread_id="main")) is False
+    assert asyncio.run(store.get(scope="default", thread_id="main")) is None
+
+
+def test_save_dedupes_multi_run_turn(monkeypatch, engine):
+    """Mirror of MAF's duplicate merge on frontend-tool roundtrips: repeated
+    message ids, a re-issued identical render call, and extra tool results."""
+    store = _store(monkeypatch, engine)
+
+    def call(cid, name, args='{"a":1}'):
+        return {"id": cid, "type": "function", "function": {"name": name, "arguments": args}}
+
+    snapshot = AGUIThreadSnapshot(
+        messages=[
+            {"id": "u1", "role": "user", "content": "resumen"},
+            {"id": "a1", "role": "assistant", "content": "",
+             "tool_calls": [call("c1", "get_cycle_summary"), call("c2", "render_spending_summary")]},
+            {"id": "t1", "role": "tool", "content": "data", "tool_call_id": "c1"},
+            # MAF re-records the resent suffix verbatim…
+            {"id": "u1", "role": "user", "content": "resumen"},
+            {"id": "t1", "role": "tool", "content": "data", "tool_call_id": "c1"},
+            {"id": "t2", "role": "tool", "content": "ok", "tool_call_id": "c2"},
+            # …plus a synthetic second result for an answered call…
+            {"id": "t3", "role": "tool", "content": "", "tool_call_id": "c1"},
+            # …and the model re-issues the same render call with a new id.
+            {"id": "a2", "role": "assistant", "content": "",
+             "tool_calls": [call("c3", "render_spending_summary")]},
+            {"id": "t4", "role": "tool", "content": "ok", "tool_call_id": "c3"},
+        ]
+    )
+    asyncio.run(store.save(scope="default", thread_id="main", snapshot=snapshot))
+
+    loaded = asyncio.run(store.get(scope="default", thread_id="main"))
+    assert [m["id"] for m in loaded.messages] == ["u1", "a1", "t1", "t2"]
+    # The duplicate render call (c3) and its result are gone; each surviving
+    # call has exactly one result.
+    assert [tc["id"] for tc in loaded.messages[1]["toolCalls"]] == ["c1", "c2"]
+    assert [(m["toolCallId"]) for m in loaded.messages if m["role"] == "tool"] == ["c1", "c2"]
+
+
+def test_clear_thread_endpoint(monkeypatch, engine, session):
+    store = _store(monkeypatch, engine)
+    assert clear_thread(session=session, _user="testadmin") == {"cleared": False}
+
+    snap = AGUIThreadSnapshot(messages=[{"id": "u1", "role": "user", "content": "x"}])
+    asyncio.run(store.save(scope="default", thread_id="main", snapshot=snap))
+
+    assert clear_thread(session=session, _user="testadmin") == {"cleared": True}
+    assert asyncio.run(store.get(scope="default", thread_id="main")) is None