feat: route workflow image inputs natively

backend/services/brains/base.py

@@ -166,11 +166,18 @@ class BaseBrain:
     def record_user_message(self, content: str) -> None:
         """Observe a committed user message for brain-owned routing state."""
 
-    async def on_user_turn_end(self, content: str) -> bool:
+    async def on_user_turn_end(
+        self,
+        content: str,
+        user_message: dict[str, Any] | None = None,
+    ) -> bool:
         """Handle a complete user turn before the conversational LLM runs.
 
         Return True when the brain scheduled the next action itself and the
         in-flight context frame must not reach the previous Agent's LLM.
+
+        ``user_message`` preserves the current universal-context message for
+        brains that need multimodal routing. Text-only brains can ignore it.
         """
         self.record_user_message(content)
         return False
@@ -222,7 +229,11 @@ class Brain(Protocol):
 
     def record_user_message(self, content: str) -> None: ...
 
-    async def on_user_turn_end(self, content: str) -> bool: ...
+    async def on_user_turn_end(
+        self,
+        content: str,
+        user_message: dict[str, Any] | None = None,
+    ) -> bool: ...
 
     async def on_assistant_text_start(self, turn_id: str) -> None: ...