fix(tui): keep image paste CI stable

src/openharness/ui/backend_host.py

@@ -368,14 +368,14 @@ class ReactBackendHost:
         async def _clear_output() -> None:
             await self._emit(BackendEvent(type="clear_transcript"))
 
-        should_continue = await handle_line(
-            self._bundle,
-            line,
-            print_system=_print_system,
-            render_event=_render_event,
-            clear_output=_clear_output,
-            user_message=user_message,
-        )
+        handle_line_kwargs: dict[str, Any] = {
+            "print_system": _print_system,
+            "render_event": _render_event,
+            "clear_output": _clear_output,
+        }
+        if user_message is not None:
+            handle_line_kwargs["user_message"] = user_message
+        should_continue = await handle_line(self._bundle, line, **handle_line_kwargs)
         if is_coordinator_mode():
             await drain_coordinator_async_agents(
                 self._bundle,

tests/test_ui/test_react_backend.py

@@ -394,10 +394,16 @@ async def test_backend_host_processes_image_turn(tmp_path, monkeypatch):
 
     assert should_continue is True
     assert len(client.requests) == 1
-    message = client.requests[0].messages[-2]
+    image_messages = [
+        message
+        for message in client.requests[0].messages
+        if message.role == "user" and any(isinstance(block, ImageBlock) for block in message.content)
+    ]
+    assert len(image_messages) == 1
+    message = image_messages[0]
     assert message.text == "Please analyze the attached image."
-    assert isinstance(message.content[1], ImageBlock)
-    assert message.content[1].data == "aGVsbG8="
+    image = next(block for block in message.content if isinstance(block, ImageBlock))
+    assert image.data == "aGVsbG8="
     assert any(
         event.type == "transcript_item"
         and event.item