Fix duplicate "Generating image..." tool call step

Only emit toolCallCreated on the in_progress event; treat the subsequent
generating event as a no-op to avoid rendering two identical steps.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: chriscarrollsmith

routers/chat.py

@@ -366,7 +366,7 @@ async def iterate_stream(s, response_id: str = "") -> AsyncGenerator[str, None]:
                                         )
                                     )
 
-                            case ResponseImageGenCallInProgressEvent() | ResponseImageGenCallGeneratingEvent():
+                            case ResponseImageGenCallInProgressEvent():
                                 current_item_id = event.item_id
                                 yield sse_format(
                                     "toolCallCreated",
@@ -377,6 +377,10 @@ async def iterate_stream(s, response_id: str = "") -> AsyncGenerator[str, None]:
                                     )
                                 )
 
+                            case ResponseImageGenCallGeneratingEvent():
+                                # Intermediate state — tool call step already created by in_progress
+                                continue
+
                             case ResponseImageGenCallPartialImageEvent():
                                 # Display partial image as it streams in
                                 img_html = (

tests/test_tool_output_rendering.py

@@ -914,11 +914,12 @@ async def test_image_gen_partial_image_emitted(self):
 
     @pytest.mark.anyio
     async def test_image_gen_no_duplicate_tool_call_on_generating(self):
-        """The generating event should not create a second toolCallCreated if in_progress already did."""
+        """The generating event should NOT create a second toolCallCreated —
+        only the in_progress event creates the tool call step."""
         events = await self._stream_events()
         tool_calls = [e for e in events if e["event"] == "toolCallCreated"]
-        # Both in_progress and generating emit toolCallCreated, but that's acceptable
-        # (they render to the same step_id so HTMX deduplicates)
-        # Just verify they all reference the same item
-        for tc in tool_calls:
-            assert f'id="step-{IG_ITEM_ID}"' in tc["data"]
+        # Only in_progress should emit toolCallCreated, not generating
+        assert len(tool_calls) == 1, (
+            f"Expected exactly 1 toolCallCreated event (from in_progress only), got {len(tool_calls)}"
+        )
+        assert f'id="step-{IG_ITEM_ID}"' in tool_calls[0]["data"]