test(harness): pin session list/show json keys + schema alias

- test_list_sessions_required_keys: assert full spec key set
  (adds summary/updated_at/author) so dropping any goes caught.
- test_cli_show_json_valid: assert "schema" in / "db_schema" not in
  data to pin by_alias=True on the alias-sensitive field.

Production code unchanged. 8 passed; full suite 230 passed.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

harness/tests/test_session_list_json.py

@@ -39,7 +39,7 @@ def test_list_sessions_required_keys(tmp_path):
     create_session("qualsiasi domanda", db, tmp_path)
     rows = _list_sessions(tmp_path)
     assert len(rows) >= 1
-    required = {"id", "status", "question", "created_at"}
+    required = {"id", "status", "question", "summary", "created_at", "updated_at", "author"}
     assert required.issubset(rows[0].keys())
 
 
@@ -136,6 +136,9 @@ def test_cli_show_json_valid(tmp_path, monkeypatch):
     assert data["id"] == m.id
     assert "phase" in data
     assert "has_schema_linking" in data
+    # Pin by_alias=True: the alias-sensitive field must serialize as "schema", not "db_schema".
+    assert "schema" in data
+    assert "db_schema" not in data
 
 
 def test_cli_show_json_stdout_pristine(tmp_path, monkeypatch):