fix(gateway): avoid cross-user mirror writes in per-user group sessions

tests/gateway/test_mirror.py

@@ -77,6 +77,46 @@ class TestFindSessionId:
 
         assert result == "sess_topic_a"
 
+    def test_user_id_disambiguates_same_group_chat(self, tmp_path):
+        sessions_dir, index_file = _setup_sessions(tmp_path, {
+            "alice": {
+                "session_id": "sess_alice",
+                "origin": {"platform": "telegram", "chat_id": "-1001", "user_id": "alice"},
+                "updated_at": "2026-01-01T00:00:00",
+            },
+            "bob": {
+                "session_id": "sess_bob",
+                "origin": {"platform": "telegram", "chat_id": "-1001", "user_id": "bob"},
+                "updated_at": "2026-02-01T00:00:00",
+            },
+        })
+
+        with patch.object(mirror_mod, "_SESSIONS_DIR", sessions_dir), \
+             patch.object(mirror_mod, "_SESSIONS_INDEX", index_file):
+            result = _find_session_id("telegram", "-1001", user_id="alice")
+
+        assert result == "sess_alice"
+
+    def test_ambiguous_same_group_chat_without_user_id_returns_none(self, tmp_path):
+        sessions_dir, index_file = _setup_sessions(tmp_path, {
+            "alice": {
+                "session_id": "sess_alice",
+                "origin": {"platform": "telegram", "chat_id": "-1001", "user_id": "alice"},
+                "updated_at": "2026-01-01T00:00:00",
+            },
+            "bob": {
+                "session_id": "sess_bob",
+                "origin": {"platform": "telegram", "chat_id": "-1001", "user_id": "bob"},
+                "updated_at": "2026-02-01T00:00:00",
+            },
+        })
+
+        with patch.object(mirror_mod, "_SESSIONS_DIR", sessions_dir), \
+             patch.object(mirror_mod, "_SESSIONS_INDEX", index_file):
+            result = _find_session_id("telegram", "-1001")
+
+        assert result is None
+
     def test_no_match_returns_none(self, tmp_path):
         sessions_dir, index_file = _setup_sessions(tmp_path, {
             "sess": {
@@ -189,6 +229,35 @@ class TestMirrorToSession:
         assert (sessions_dir / "sess_topic_a.jsonl").exists()
         assert not (sessions_dir / "sess_topic_b.jsonl").exists()
 
+    def test_successful_mirror_uses_user_id_for_group_session(self, tmp_path):
+        sessions_dir, index_file = _setup_sessions(tmp_path, {
+            "alice": {
+                "session_id": "sess_alice",
+                "origin": {"platform": "telegram", "chat_id": "-1001", "user_id": "alice"},
+                "updated_at": "2026-01-01T00:00:00",
+            },
+            "bob": {
+                "session_id": "sess_bob",
+                "origin": {"platform": "telegram", "chat_id": "-1001", "user_id": "bob"},
+                "updated_at": "2026-02-01T00:00:00",
+            },
+        })
+
+        with patch.object(mirror_mod, "_SESSIONS_DIR", sessions_dir), \
+             patch.object(mirror_mod, "_SESSIONS_INDEX", index_file), \
+             patch("gateway.mirror._append_to_sqlite"):
+            result = mirror_to_session(
+                "telegram",
+                "-1001",
+                "Hello group!",
+                source_label="cli",
+                user_id="alice",
+            )
+
+        assert result is True
+        assert (sessions_dir / "sess_alice.jsonl").exists()
+        assert not (sessions_dir / "sess_bob.jsonl").exists()
+
     def test_no_matching_session(self, tmp_path):
         sessions_dir, index_file = _setup_sessions(tmp_path, {})
 

tests/tools/test_send_message_tool.py

@@ -167,6 +167,39 @@ class TestSendMessageTool:
             media_files=[],
         )
 
+    def test_mirror_receives_current_session_user_id(self):
+        config, _telegram_cfg = _make_config()
+
+        with patch("gateway.config.load_gateway_config", return_value=config), \
+             patch("tools.interrupt.is_interrupted", return_value=False), \
+             patch("model_tools._run_async", side_effect=_run_async_immediately), \
+             patch("tools.send_message_tool._send_to_platform", new=AsyncMock(return_value={"success": True})), \
+             patch("gateway.session_context.get_session_env") as get_session_env_mock, \
+             patch("gateway.mirror.mirror_to_session", return_value=True) as mirror_mock:
+            get_session_env_mock.side_effect = lambda name, default="": {
+                "HERMES_SESSION_PLATFORM": "telegram",
+                "HERMES_SESSION_USER_ID": "user-123",
+            }.get(name, default)
+            result = json.loads(
+                send_message_tool(
+                    {
+                        "action": "send",
+                        "target": "telegram:12345",
+                        "message": "hello",
+                    }
+                )
+            )
+
+        assert result["success"] is True
+        mirror_mock.assert_called_once_with(
+            "telegram",
+            "12345",
+            "hello",
+            source_label="telegram",
+            thread_id=None,
+            user_id="user-123",
+        )
+
     def test_top_level_send_failure_redacts_query_token(self):
         config, _telegram_cfg = _make_config()
         leaked = "very-secret-query-token-123456"