test(sessions): wire sessions_dir through auto-prune + file-cleanup regression tests

- TestAutoMaintenance gains 3 tests: auto-prune deletes transcript files
  when sessions_dir is passed, preserves them when it isn't (backward-
  compat), and never touches active-session files during prune.
- FakeDB helpers in test_sessions_delete.py accept **kwargs so they
  don't break when delete_session signature gains sessions_dir.

tests/hermes_cli/test_sessions_delete.py

@@ -12,7 +12,7 @@ def test_sessions_delete_accepts_unique_id_prefix(monkeypatch, capsys):
             captured["resolved_from"] = session_id
             return "20260315_092437_c9a6ff"
 
-        def delete_session(self, session_id):
+        def delete_session(self, session_id, **kwargs):
             captured["deleted"] = session_id
             return True
 
@@ -45,7 +45,7 @@ def test_sessions_delete_reports_not_found_when_prefix_is_unknown(monkeypatch, c
         def resolve_session_id(self, session_id):
             return None
 
-        def delete_session(self, session_id):
+        def delete_session(self, session_id, **kwargs):
             raise AssertionError("delete_session should not be called when resolution fails")
 
         def close(self):
@@ -73,7 +73,7 @@ def test_sessions_delete_handles_eoferror_on_confirm(monkeypatch, capsys):
         def resolve_session_id(self, session_id):
             return "20260315_092437_c9a6ff"
 
-        def delete_session(self, session_id):
+        def delete_session(self, session_id, **kwargs):
             raise AssertionError("delete_session should not be called when cancelled")
 
         def close(self):

tests/test_hermes_state.py

@@ -1981,3 +1981,58 @@ class TestAutoMaintenance:
         # Should parse as a float timestamp close to now.
         assert abs(float(marker) - time.time()) < 60
 
+    def test_auto_prune_deletes_transcript_files(self, db, tmp_path):
+        """Issue #3015: auto-prune must also delete on-disk transcript files."""
+        sessions_dir = tmp_path / "sessions"
+        sessions_dir.mkdir()
+
+        self._make_old_ended(db, "old1", days_old=100)
+        self._make_old_ended(db, "old2", days_old=100)
+        db.create_session(session_id="new", source="cli")  # active
+
+        # Transcript files mimicking real gateway/CLI layout
+        (sessions_dir / "old1.json").write_text("{}")
+        (sessions_dir / "old1.jsonl").write_text("{}\n")
+        (sessions_dir / "old2.jsonl").write_text("{}\n")
+        (sessions_dir / "request_dump_old1_001.json").write_text("{}")
+        (sessions_dir / "new.jsonl").write_text("{}\n")  # active, must survive
+
+        result = db.maybe_auto_prune_and_vacuum(
+            retention_days=90, sessions_dir=sessions_dir
+        )
+        assert result["pruned"] == 2
+
+        # Pruned transcript files are gone
+        assert not (sessions_dir / "old1.json").exists()
+        assert not (sessions_dir / "old1.jsonl").exists()
+        assert not (sessions_dir / "old2.jsonl").exists()
+        assert not (sessions_dir / "request_dump_old1_001.json").exists()
+        # Active session's transcript is untouched
+        assert (sessions_dir / "new.jsonl").exists()
+
+    def test_auto_prune_without_sessions_dir_preserves_files(self, db, tmp_path):
+        """Backward-compat: no sessions_dir = DB-only cleanup (legacy behavior)."""
+        sessions_dir = tmp_path / "sessions"
+        sessions_dir.mkdir()
+        self._make_old_ended(db, "old", days_old=100)
+        (sessions_dir / "old.jsonl").write_text("{}\n")
+
+        result = db.maybe_auto_prune_and_vacuum(retention_days=90)
+        assert result["pruned"] == 1
+        # File stays — caller didn't opt in
+        assert (sessions_dir / "old.jsonl").exists()
+
+    def test_prune_sessions_deletes_files_for_pruned_only(self, db, tmp_path):
+        """Active-session transcripts must never be deleted by prune."""
+        sessions_dir = tmp_path / "sessions"
+        sessions_dir.mkdir()
+        self._make_old_ended(db, "old", days_old=100)
+        db.create_session(session_id="active", source="cli")  # not ended
+        (sessions_dir / "old.jsonl").write_text("{}\n")
+        (sessions_dir / "active.jsonl").write_text("{}\n")
+
+        count = db.prune_sessions(older_than_days=90, sessions_dir=sessions_dir)
+        assert count == 1
+        assert not (sessions_dir / "old.jsonl").exists()
+        assert (sessions_dir / "active.jsonl").exists()
+