fix(gateway): isolate pending native image paths by session

gateway/run.py

@@ -884,6 +884,7 @@ class GatewayRunner:
         # /new and /reset.  /model and other mid-session operations
         # preserve the queue.
         self._queued_events: Dict[str, List[MessageEvent]] = {}
+        self._pending_native_image_paths_by_session: Dict[str, List[str]] = {}
         self._busy_ack_ts: Dict[str, float] = {}  # last busy-ack timestamp per session (debounce)
         self._session_run_generation: Dict[str, int] = {}
 
@@ -5079,22 +5080,30 @@ class GatewayRunner:
         preprocessing pipeline so sender attribution, image enrichment, STT,
         document notes, reply context, and @ references all behave the same.
 
-        Side effect: writes ``self._pending_native_image_paths`` to a list of
-        local image paths when the active model supports native vision AND
-        the user has images attached. The caller consumes and clears this
-        attribute at the ``run_conversation`` site to build a multimodal user
-        turn. When the list is empty, the ``_enrich_message_with_vision``
-        text path has already run and images are represented in-text.
+        Side effect: buffers per-session native image paths when the active
+        model supports native vision AND the user has images attached. The
+        caller consumes and clears that session-scoped buffer at the
+        ``run_conversation`` site to build a multimodal user turn. When the
+        list is empty, the ``_enrich_message_with_vision`` text path has
+        already run and images are represented in-text.
         """
         history = history or []
         message_text = event.text or ""
-        # Reset per-call buffer; set only when native routing is chosen.
-        self._pending_native_image_paths = []
+        _group_sessions_per_user = getattr(self.config, "group_sessions_per_user", True)
+        _thread_sessions_per_user = getattr(self.config, "thread_sessions_per_user", False)
+        session_key = build_session_key(
+            source,
+            group_sessions_per_user=_group_sessions_per_user,
+            thread_sessions_per_user=_thread_sessions_per_user,
+        )
+        # Reset only this session's per-call buffer; other sessions may be
+        # concurrently preparing multimodal turns on the same runner.
+        self._consume_pending_native_image_paths(session_key)
 
         _is_shared_multi_user = is_shared_multi_user_session(
             source,
-            group_sessions_per_user=getattr(self.config, "group_sessions_per_user", True),
-            thread_sessions_per_user=getattr(self.config, "thread_sessions_per_user", False),
+            group_sessions_per_user=_group_sessions_per_user,
+            thread_sessions_per_user=_thread_sessions_per_user,
         )
         if _is_shared_multi_user and source.user_name:
             message_text = f"[{source.user_name}] {message_text}"
@@ -5115,7 +5124,11 @@ class GatewayRunner:
                 _img_mode = self._decide_image_input_mode()
                 if _img_mode == "native":
                     # Defer attachment to the run_conversation call site.
-                    self._pending_native_image_paths = list(image_paths)
+                    pending_native = getattr(self, "_pending_native_image_paths_by_session", None)
+                    if pending_native is None:
+                        pending_native = {}
+                        self._pending_native_image_paths_by_session = pending_native
+                    pending_native[session_key] = list(image_paths)
                     logger.info(
                         "Image routing: native (model supports vision). %d image(s) will be attached inline.",
                         len(image_paths),
@@ -5254,6 +5267,12 @@ class GatewayRunner:
 
         return message_text
 
+    def _consume_pending_native_image_paths(self, session_key: str) -> List[str]:
+        pending_native = getattr(self, "_pending_native_image_paths_by_session", None)
+        if not pending_native:
+            return []
+        return list(pending_native.pop(session_key, []) or [])
+
     async def _handle_message_with_agent(self, event, source, _quick_key: str, run_generation: int):
         """Inner handler that runs under the _running_agents sentinel guard."""
         _msg_start_time = time.time()
@@ -12136,8 +12155,7 @@ class GatewayRunner:
                 # attachment, wrap the user turn as an OpenAI-style multimodal
                 # content list. Consume-and-clear so subsequent turns on the same
                 # runner instance don't re-attach stale images.
-                _native_imgs = list(getattr(self, "_pending_native_image_paths", []) or [])
-                self._pending_native_image_paths = []
+                _native_imgs = self._consume_pending_native_image_paths(session_key)
                 if _native_imgs:
                     try:
                         from agent.image_routing import build_native_content_parts