Emit streamed image-generation result on output_item.done when no partial was sent

provider/openaiprovider/responses.go

@@ -1357,6 +1357,10 @@ type responsesStreamState struct {
 	messageID           string
 	role                message.Role
 	anyFunctions        bool
+	// imagePartialsSeen records image-generation item IDs that emitted a
+	// partial_image event, so the output_item.done handler does not emit a
+	// duplicate final image for them.
+	imagePartialsSeen map[string]bool
 }
 
 // responsesProcessStreamingUpdate processes a streaming update from the Responses API.
@@ -1532,6 +1536,10 @@ func responsesProcessStreamingUpdate(update responses.ResponseStreamEventUnion,
 		}
 
 	case responses.ResponseImageGenCallPartialImageEvent:
+		if state.imagePartialsSeen == nil {
+			state.imagePartialsSeen = map[string]bool{}
+		}
+		state.imagePartialsSeen[event.ItemID] = true
 		result := imageGenerationResult(event.ItemID, event.PartialImageB64, cmp.Or(event.OutputFormat, "png"), event)
 		result.Outputs[0].Header().AdditionalProperties = map[string]any{
 			"ItemId":            event.ItemID,
@@ -1626,7 +1634,13 @@ func responsesProcessStreamingUpdate(update responses.ResponseStreamEventUnion,
 		case responses.ResponseFunctionWebSearch:
 			u.Contents = webSearchContents(item)
 		case responses.ResponseOutputItemImageGenerationCall:
-			// Dedicated image-generation events emit the call and partial results.
+			// The dedicated partial_image events emit the image incrementally, but
+			// they are only sent when partial_images > 0. In the default case no
+			// partial event arrives and the finished image lives on the done item,
+			// so emit it here unless a partial was already seen for this item.
+			if !state.imagePartialsSeen[item.ID] {
+				u.Contents = imageGenerationContents(item)
+			}
 		case responses.ResponseReasoningItem:
 			// Carry the completed reasoning item's encrypted content so it can be
 			// replayed on the next turn when store=false (reasoning delta events only

provider/openaiprovider/responses_test.go

@@ -7779,3 +7779,52 @@ func TestResponsesToolResult_StructSerializedAsJSON(t *testing.T) {
 		t.Errorf("tool result was not JSON-encoded (missing field temp_c):\n%s", captured)
 	}
 }
+
+func TestResponsesStreamingImageGenerationCall_NoPartial_EmitsResultOnDone(t *testing.T) {
+	// The partial_image events are only sent when partial_images > 0. In the
+	// default case the finished image arrives only on output_item.done, so the
+	// result must still be surfaced from there.
+	const imageBase64 = "iVBORw0KGgo="
+	const input = `
+            {
+                "model":"gpt-4o-mini",
+                "input":[{"type":"message","role":"user","content":[{"type":"input_text","text":"draw"}]}],
+                "stream":true
+            }
+            `
+	const output = `event: response.created
+data: {"type":"response.created","sequence_number":0,"response":{"id":"resp_001","object":"response","created_at":1741892091,"status":"in_progress","model":"gpt-4o-mini","output":[]}}
+
+event: response.image_generation_call.in_progress
+data: {"type":"response.image_generation_call.in_progress","sequence_number":1,"output_index":0,"item_id":"ig_123"}
+
+event: response.output_item.done
+data: {"type":"response.output_item.done","sequence_number":2,"output_index":0,"item":{"type":"image_generation_call","id":"ig_123","status":"completed","result":"` + imageBase64 + `"}}
+
+event: response.completed
+data: {"type":"response.completed","sequence_number":3,"response":{"id":"resp_001","object":"response","created_at":1741892091,"status":"completed","model":"gpt-4o-mini","output":[]}}
+
+`
+	server := newTestResponsesServerStreaming(t, input, output)
+	defer server.Close()
+
+	a := newTestResponsesClient(server, "gpt-4o-mini")
+	var result *message.ImageGenerationToolResultContent
+	for update, err := range a.RunText(t.Context(), "draw", agent.Stream(true)) {
+		if err != nil {
+			t.Fatalf("error = %v", err)
+		}
+		for _, content := range update.Contents {
+			if r, ok := content.(*message.ImageGenerationToolResultContent); ok {
+				result = r
+			}
+		}
+	}
+	if result == nil || result.CallID != "ig_123" || len(result.Outputs) != 1 {
+		t.Fatalf("result = %#v, want one output for CallID ig_123", result)
+	}
+	image, ok := result.Outputs[0].(*message.DataContent)
+	if !ok || image.Data != imageBase64 {
+		t.Fatalf("output = %#v, want DataContent with the image", result.Outputs[0])
+	}
+}