fix: use self._session_db directly + add regression test

- Replace getattr(self.session_store, '_db', None) with self._session_db
  (the GatewayRunner's own SessionDB, consistent with existing usage in
  slash_commands.py L240/L499).
- Remove verbose comment referencing a branch name as an issue number.
- Update stale comment in run.py that said 'today it has no session_db'.
- Add regression test verifying session_db is passed and rotated session
  is persisted (adapted from #51624 by @LeonSGP43).
- Add _session_db=None to _make_runner fixtures in test_compress_command,
  test_compress_focus, and test_compress_plugin_engine.

gateway/run.py

@@ -9542,7 +9542,6 @@ class GatewayRunner(GatewayAuthorizationMixin, GatewayKanbanWatchersMixin, Gatew
                             ]
 
                             if len(_hyg_msgs) >= 4:
-                                _hyg_session_db = getattr(self.session_store, "_db", None)
                                 _hyg_agent = AIAgent(
                                     **_hyg_runtime,
                                     model=_hyg_model,
@@ -9551,15 +9550,15 @@ class GatewayRunner(GatewayAuthorizationMixin, GatewayKanbanWatchersMixin, Gatew
                                     skip_memory=True,
                                     enabled_toolsets=["memory"],
                                     session_id=session_entry.session_id,
-                                    session_db=_hyg_session_db,
+                                    session_db=self._session_db,
                                 )
                                 try:
                                     # The hygiene agent rotates the session
                                     # forward to a continuation id that becomes
                                     # the gateway session's live row. It must
-                                    # never finalize on close() (today it has no
-                                    # session_db so close() no-ops, but this
-                                    # guards a future where one is wired in).
+                                    # never finalize on close() — close() would
+                                    # end the newly rotated session the gateway
+                                    # entry now points at.
                                     _hyg_agent._end_session_on_close = False
                                     _hyg_agent._print_fn = lambda *a, **kw: None
 

gateway/slash_commands.py

@@ -2810,12 +2810,6 @@ class GatewaySlashCommandsMixin:
                     partial = False
                     head = msgs
 
-            # Pass session_db so the temp agent can persist its session
-            # rotation to the database. Without it, compress_context computes
-            # the compressed messages in memory but never writes them to the
-            # session store — the next user message reloads the full original
-            # transcript and the apparent compression is lost (#fix/compress-gateway-persistence).
-            _tmp_session_db = getattr(self.session_store, "_db", None)
             tmp_agent = AIAgent(
                 **runtime_kwargs,
                 model=model,
@@ -2824,7 +2818,7 @@ class GatewaySlashCommandsMixin:
                 skip_memory=True,
                 enabled_toolsets=["memory"],
                 session_id=session_entry.session_id,
-                session_db=_tmp_session_db,
+                session_db=self._session_db,
             )
             try:
                 tmp_agent._print_fn = lambda *a, **kw: None

tests/gateway/test_compress_command.py

@@ -54,6 +54,7 @@ def _make_runner(history: list[dict[str, str]]):
     runner.session_store.rewrite_transcript = MagicMock()
     runner.session_store.update_session = MagicMock()
     runner.session_store._save = MagicMock()
+    runner._session_db = None
     return runner
 
 
@@ -247,3 +248,60 @@ async def test_compress_command_surfaces_aux_model_failure_even_when_recovered()
     assert "intact" in result
     agent_instance.shutdown_memory_provider.assert_called_once()
     agent_instance.close.assert_called_once()
+
+
+@pytest.mark.asyncio
+async def test_compress_command_passes_session_db_and_persists_rotated_session():
+    """session_db must be wired into the /compress temp agent so that
+    _compress_context can actually rotate the session and persist the
+    compressed transcript — without it compression is a silent no-op."""
+    history = _make_history()
+    compressed = [
+        history[0],
+        {"role": "assistant", "content": "compressed summary"},
+        history[-1],
+    ]
+    runner = _make_runner(history)
+    runner._session_db = object()
+    agent_instance = MagicMock()
+    agent_instance.shutdown_memory_provider = MagicMock()
+    agent_instance.close = MagicMock()
+    agent_instance._cached_system_prompt = ""
+    agent_instance.tools = None
+    agent_instance.context_compressor.has_content_to_compress.return_value = True
+    agent_instance.compression_in_place = False
+    agent_instance.session_id = "sess-1"
+
+    def _compress(messages, *_args, **_kwargs):
+        agent_instance.session_id = "sess-2"
+        return compressed, ""
+
+    agent_instance._compress_context.side_effect = _compress
+
+    def _estimate(messages, **_kwargs):
+        if messages == history:
+            return 100
+        if messages == compressed:
+            return 60
+        raise AssertionError(f"unexpected transcript: {messages!r}")
+
+    with (
+        patch("gateway.run._resolve_runtime_agent_kwargs", return_value={"api_key": "***"}),
+        patch("gateway.run._resolve_gateway_model", return_value="test-model"),
+        patch("run_agent.AIAgent", return_value=agent_instance) as mock_agent_cls,
+        patch("agent.model_metadata.estimate_request_tokens_rough", side_effect=_estimate),
+    ):
+        result = await runner._handle_compress_command(_make_event())
+
+    assert "Compressed:" in result
+    mock_agent_cls.assert_called_once()
+    assert mock_agent_cls.call_args.kwargs["session_db"] is runner._session_db
+    runner.session_store._save.assert_called_once()
+    runner.session_store.rewrite_transcript.assert_called_once_with(
+        "sess-2", compressed
+    )
+    runner.session_store.update_session.assert_called_once_with(
+        build_session_key(_make_source()), last_prompt_tokens=0
+    )
+    agent_instance.shutdown_memory_provider.assert_called_once()
+    agent_instance.close.assert_called_once()

tests/gateway/test_compress_focus.py

@@ -54,6 +54,7 @@ def _make_runner(history: list[dict[str, str]]):
     runner.session_store.rewrite_transcript = MagicMock()
     runner.session_store.update_session = MagicMock()
     runner.session_store._save = MagicMock()
+    runner._session_db = None
     return runner
 
 

tests/gateway/test_compress_plugin_engine.py

@@ -101,6 +101,7 @@ def _make_runner(history: list[dict[str, str]]):
     runner.session_store.rewrite_transcript = MagicMock()
     runner.session_store.update_session = MagicMock()
     runner.session_store._save = MagicMock()
+    runner._session_db = None
     return runner