fix(gateway): clear session-scoped model overrides on /resume

/resume is a conversation boundary, but unlike /new it did not clear the
chat-keyed _session_model_overrides / _pending_model_notes. A /model switch
made in the previous session under the same chat session_key leaked into the
resumed conversation, running it on the wrong model.

Clear both maps for the session_key after the switch (mirroring /new), scoped
to that key so other chats' overrides are untouched. The cached-agent eviction
this leak also implied already landed via #6672.

Closes #10702.

gateway/slash_commands.py

@@ -3233,6 +3233,20 @@ class GatewaySlashCommandsMixin:
             return t("gateway.resume.switch_failed")
         self._clear_session_boundary_security_state(session_key)
 
+        # Clear session-scoped model/reasoning overrides so the resumed
+        # conversation picks up configured defaults instead of a /model
+        # switch made in the previous session under the same chat
+        # session_key. /resume is a conversation boundary just like /new
+        # (which clears these too); without this, a stale override leaks
+        # across the switch. See #10702.
+        _overrides = getattr(self, "_session_model_overrides", None)
+        if isinstance(_overrides, dict):
+            _overrides.pop(session_key, None)
+        self._set_session_reasoning_override(session_key, None)
+        _pending_notes = getattr(self, "_pending_model_notes", None)
+        if isinstance(_pending_notes, dict):
+            _pending_notes.pop(session_key, None)
+
         # Evict any cached agent for this session so the next message
         # rebuilds with the correct session_id end-to-end — mirrors
         # /branch and /reset. Without this, the cached AIAgent (and its

tests/gateway/test_resume_command.py

@@ -173,6 +173,40 @@ class TestHandleResumeCommand:
         assert call_args[0][1] == "old_session_abc"
         db.close()
 
+    @pytest.mark.asyncio
+    async def test_resume_clears_session_model_overrides(self, tmp_path):
+        """Resume must not carry a previous session's /model override into the
+        restored conversation, while leaving other chats' overrides intact (#10702)."""
+        from hermes_state import SessionDB
+        db = SessionDB(db_path=tmp_path / "state.db")
+        db.create_session("old_session_abc", "telegram")
+        db.set_session_title("old_session_abc", "My Project")
+        db.create_session("current_session_001", "telegram")
+
+        event = _make_event(text="/resume My Project")
+        runner = _make_runner(session_db=db, current_session_id="current_session_001",
+                              event=event)
+        key = _session_key_for_event(event)
+        runner._session_model_overrides = {
+            key: {"model": "gpt-5", "provider": "openai"},
+            "agent:main:telegram:dm:other": {"model": "keep-me"},
+        }
+        runner._pending_model_notes = {
+            key: "[Note: switched to gpt-5]",
+            "agent:main:telegram:dm:other": "[Note: keep-me]",
+        }
+
+        result = await runner._handle_resume_command(event)
+
+        assert "Resumed" in result
+        # The resumed chat's override + pending note are cleared...
+        assert key not in runner._session_model_overrides
+        assert key not in runner._pending_model_notes
+        # ...but an unrelated chat's state is untouched.
+        assert runner._session_model_overrides["agent:main:telegram:dm:other"] == {"model": "keep-me"}
+        assert runner._pending_model_notes["agent:main:telegram:dm:other"] == "[Note: keep-me]"
+        db.close()
+
     @pytest.mark.asyncio
     async def test_resume_nonexistent_name(self, tmp_path):
         """Returns error for unknown session name."""