wip(handoff): restore backend suite to green

Co-Authored-By: Codex <noreply@openai.com>

backend/tests/test_branch_manager.py

@@ -66,6 +66,7 @@ async def test_create_fork(client: AsyncClient, test_user, auth_headers, test_db
 
     step = AISessionStep(
         session_id=session.id,
+        account_id=session.account_id,
         step_order=0,
         step_type="question",
         content={"text": "What's the issue?"},
@@ -119,7 +120,7 @@ async def test_switch_branch(client: AsyncClient, test_user, auth_headers, test_
     root = await manager.create_root_branch(session.id)
 
     step = AISessionStep(
-        session_id=session.id, step_order=0, step_type="question",
+        session_id=session.id, account_id=session.account_id, step_order=0, step_type="question",
         content={"text": "test"}, confidence_at_step=0.5,
     )
     test_db.add(step)
@@ -197,7 +198,7 @@ async def test_get_branch_tree(client: AsyncClient, test_user, auth_headers, tes
     root = await manager.create_root_branch(session.id)
 
     step = AISessionStep(
-        session_id=session.id, step_order=0, step_type="question",
+        session_id=session.id, account_id=session.account_id, step_order=0, step_type="question",
         content={"text": "test"}, confidence_at_step=0.5,
     )
     test_db.add(step)