fix(session): resolve default state DB path at call time

DEFAULT_DB_PATH in hermes_state.py is computed at import time, freezing
the developer's real ~/.hermes even when a test fixture (or runtime
profile switch) later redirects HERMES_HOME. Any default SessionDB() —
e.g. gateway SessionStore — then opened the real state.db.

Add _default_db_path(): resolves get_hermes_home() fresh at call time,
while a deliberately re-pointed DEFAULT_DB_PATH (the established
monkeypatch escape hatch) still wins via an import-time snapshot
comparison, preserving existing test behavior. SessionDB.__init__ and
session_search's requirement check now use the resolver; explicit
db_path arguments are untouched.

Reimplemented from PR #11875 by @JorkeyLiu (original diff predates the
hermes_state rewrite); regression test ported and modernized.

contributors/emails/jorkeyliu@gmail.com

@@ -0,0 +1,2 @@
+JorkeyLiu
+# PR #11875 salvage

hermes_state.py

@@ -234,6 +234,30 @@ T = TypeVar("T")
 
 DEFAULT_DB_PATH = get_hermes_home() / "state.db"
 
+# Import-time snapshot used by _default_db_path() to detect a deliberately
+# re-pointed DEFAULT_DB_PATH (tests monkeypatch the constant directly).
+_IMPORT_DEFAULT_DB_PATH = DEFAULT_DB_PATH
+
+
+def _default_db_path() -> Path:
+    """Resolve the default state DB path at call time.
+
+    ``DEFAULT_DB_PATH`` is computed when this module is first imported, which
+    freezes the developer's real ``~/.hermes`` even when a test fixture later
+    redirects ``HERMES_HOME`` — importing this module during collection was
+    enough to point every default ``SessionDB()`` at the real state.db.
+
+    Precedence:
+
+    1. A deliberately re-pointed ``DEFAULT_DB_PATH`` (differs from the
+       import-time snapshot — the established test escape hatch) wins.
+    2. Otherwise resolve ``get_hermes_home()`` fresh so a runtime
+       ``HERMES_HOME`` redirect takes effect regardless of import order.
+    """
+    if DEFAULT_DB_PATH != _IMPORT_DEFAULT_DB_PATH:
+        return DEFAULT_DB_PATH
+    return get_hermes_home() / "state.db"
+
 # ---------------------------------------------------------------------------
 # WAL-compatibility fallback
 # ---------------------------------------------------------------------------
@@ -1765,7 +1789,7 @@ class SessionDB(SessionSearchMixin, SessionSchemaMixin, SessionPortabilityMixin)
     _IMPORT_MAX_TOTAL_BYTES = 25 * 1024 * 1024
 
     def __init__(self, db_path: Path = None, read_only: bool = False):
-        self.db_path = db_path or DEFAULT_DB_PATH
+        self.db_path = db_path or _default_db_path()
         self.read_only = read_only
 
         self._lock = threading.Lock()

tests/gateway/test_session_store_prune.py

@@ -24,6 +24,29 @@ from gateway.config import GatewayConfig, Platform, SessionResetPolicy
 from gateway.session import SessionEntry, SessionStore
 
 
+def test_session_store_default_db_uses_runtime_hermes_home(tmp_path, monkeypatch):
+    """SessionStore must honor runtime HERMES_HOME when opening the default DB.
+
+    Regression for the import-time DEFAULT_DB_PATH freeze: importing
+    hermes_state before a fixture redirected HERMES_HOME used to pin every
+    default SessionDB() at the developer's real ~/.hermes/state.db.
+    """
+    config = GatewayConfig(default_reset_policy=SessionResetPolicy(mode="none"))
+    fake_home = tmp_path / "alt_hermes_home"
+    fake_home.mkdir()
+    monkeypatch.setenv("HERMES_HOME", str(fake_home))
+
+    with patch("gateway.session.SessionStore._ensure_loaded"):
+        store = SessionStore(sessions_dir=tmp_path / "sessions", config=config)
+
+    try:
+        assert store._db is not None
+        assert store._db.db_path == fake_home / "state.db"
+    finally:
+        if store._db is not None:
+            store._db.close()
+
+
 def _make_store(tmp_path, max_age_days: int = 90, has_active_processes_fn=None):
     """Build a SessionStore bypassing SQLite/disk-load side effects."""
     config = GatewayConfig(

tools/session_search_tool.py

@@ -954,8 +954,8 @@ def session_search(
 def check_session_search_requirements() -> bool:
     """Requires the SQLite state database."""
     try:
-        from hermes_state import DEFAULT_DB_PATH
-        return DEFAULT_DB_PATH.parent.exists()
+        from hermes_state import _default_db_path
+        return _default_db_path().parent.exists()
     except ImportError:
         return False