test(gateway): pin DEFAULT_DB_PATH in fixtures to prevent real state.db writes

Fixtures that instantiate SessionStore() trigger SessionDB() with no args,
which resolves to ~/.hermes/state.db via the DEFAULT_DB_PATH module constant
(snapshot of get_hermes_home() at hermes_state import time).

The autouse _hermetic_environment fixture in tests/conftest.py monkeypatches
HERMES_HOME env, but DEFAULT_DB_PATH is already cached by then. Per-test
monkeypatch.setattr(hermes_state, 'DEFAULT_DB_PATH', tmp_path/'state.db')
forces the DB into tmp_path so the tests can't leak into the real profile.

Verified by counting u1-prefixed sessions in real state.db before/after:
delta=0.

tests/gateway/platforms/test_yuanbao_recall_db_only.py

@@ -3,8 +3,15 @@ from gateway.session import SessionStore
 from gateway.config import GatewayConfig
 
 
-def test_recall_falls_through_to_content_match_without_message_id(tmp_path):
-    """When transcript has no message_id field, A2 content-match still works."""
+def test_recall_falls_through_to_content_match_without_message_id(tmp_path, monkeypatch):
+    """When transcript has no message_id field, A2 content-match still works.
+
+    Pin DEFAULT_DB_PATH to tmp_path so SessionDB() can't write to the real
+    ~/.hermes/state.db. (Module-level constant snapshot, see test_load_transcript_db_only.)
+    """
+    import hermes_state
+    monkeypatch.setattr(hermes_state, "DEFAULT_DB_PATH", tmp_path / "state.db")
+
     config = GatewayConfig()
     store = SessionStore(sessions_dir=tmp_path, config=config)
 

tests/gateway/test_load_transcript_db_only.py

@@ -1,13 +1,23 @@
 """Verify load_transcript returns SQLite messages without any JSONL file."""
 from pathlib import Path
+
 import pytest
 
 from gateway.session import SessionStore
 from gateway.config import GatewayConfig
 
 
-def test_load_transcript_returns_db_messages_when_no_jsonl(tmp_path):
-    """Reading a transcript must work from SQLite alone — no JSONL fallback needed."""
+def test_load_transcript_returns_db_messages_when_no_jsonl(tmp_path, monkeypatch):
+    """Reading a transcript must work from SQLite alone — no JSONL fallback needed.
+
+    Pin DEFAULT_DB_PATH to tmp_path so this test cannot write to the real
+    ~/.hermes/state.db. (DEFAULT_DB_PATH is a module-level constant computed
+    at hermes_state import time, before pytest's HERMES_HOME monkeypatch
+    fires — the autouse fixture's HERMES_HOME override doesn't help here.)
+    """
+    import hermes_state
+    monkeypatch.setattr(hermes_state, "DEFAULT_DB_PATH", tmp_path / "state.db")
+
     config = GatewayConfig()
     store = SessionStore(sessions_dir=tmp_path, config=config)
 
@@ -16,11 +26,6 @@ def test_load_transcript_returns_db_messages_when_no_jsonl(tmp_path):
     store.append_to_transcript(sid, {"role": "user", "content": "hello", "timestamp": 1.0})
     store.append_to_transcript(sid, {"role": "assistant", "content": "world", "timestamp": 2.0})
 
-    # Delete any JSONL that the current dual-writer left behind
-    jsonl_path = tmp_path / f"{sid}.jsonl"
-    if jsonl_path.exists():
-        jsonl_path.unlink()
-
     history = store.load_transcript(sid)
     assert len(history) == 2
     assert history[0]["content"] == "hello"

tests/gateway/test_session.py

@@ -504,7 +504,9 @@ class TestSessionStoreRewriteTranscript:
     """Regression: /retry and /undo must persist truncated history to DB."""
 
     @pytest.fixture()
-    def store(self, tmp_path):
+    def store(self, tmp_path, monkeypatch):
+        import hermes_state
+        monkeypatch.setattr(hermes_state, "DEFAULT_DB_PATH", tmp_path / "state.db")
         config = GatewayConfig()
         s = SessionStore(sessions_dir=tmp_path, config=config)
         return s
@@ -546,13 +548,17 @@ class TestSessionStoreRewriteTranscript:
 class TestLoadTranscriptDBOnly:
     """After spec 002, load_transcript reads only from state.db."""
 
-    def test_db_only_returns_empty_for_nonexistent(self, tmp_path):
+    def test_db_only_returns_empty_for_nonexistent(self, tmp_path, monkeypatch):
+        import hermes_state
+        monkeypatch.setattr(hermes_state, "DEFAULT_DB_PATH", tmp_path / "state.db")
         config = GatewayConfig()
         store = SessionStore(sessions_dir=tmp_path, config=config)
         result = store.load_transcript("nonexistent")
         assert result == []
 
-    def test_db_only_returns_messages(self, tmp_path):
+    def test_db_only_returns_messages(self, tmp_path, monkeypatch):
+        import hermes_state
+        monkeypatch.setattr(hermes_state, "DEFAULT_DB_PATH", tmp_path / "state.db")
         config = GatewayConfig()
         store = SessionStore(sessions_dir=tmp_path, config=config)
         sid = "db_only_session"

tests/gateway/test_session_dm_thread_seeding.py

@@ -22,8 +22,16 @@ from gateway.session import SessionSource, SessionStore, build_session_key
 
 
 @pytest.fixture()
-def store(tmp_path):
-    """SessionStore with SQLite — load_transcript reads from DB only."""
+def store(tmp_path, monkeypatch):
+    """SessionStore with SQLite — load_transcript reads from DB only.
+
+    Pin DEFAULT_DB_PATH to tmp_path so SessionDB() can't write to the real
+    ~/.hermes/state.db. (DEFAULT_DB_PATH is a module-level constant computed
+    at hermes_state import time, before pytest's HERMES_HOME monkeypatch
+    fires — the autouse fixture's HERMES_HOME override doesn't help here.)
+    """
+    import hermes_state
+    monkeypatch.setattr(hermes_state, "DEFAULT_DB_PATH", tmp_path / "state.db")
     config = GatewayConfig()
     s = SessionStore(sessions_dir=tmp_path, config=config)
     return s