fix(providers/openai): emit source parts for Responses API streaming annotations

The Responses API streaming path was missing a handler for
"response.output_text.annotation.added" events. This meant that
url_citation and file_citation annotations—which carry source
URLs and titles for web search results—were silently dropped
during streaming.

The non-streaming Generate path and the Chat Completions API
streaming path both handled annotations correctly; only the
Responses API Stream path was affected.

Add a case for "response.output_text.annotation.added" that
parses the annotation map and yields StreamPartTypeSource parts
for url_citation and file_citation types, matching the behavior
of the existing Generate path and the Anthropic provider.

Update TestResponsesStream_WebSearchResponse to include
annotation.added events in the mock stream and assert that
source parts are emitted with the correct URL, title, and type.

Author: kylecarbs

providers/openai/openai_test.go

@@ -4061,8 +4061,12 @@ func TestResponsesStream_WebSearchResponse(t *testing.T) {
 			`data: {"type":"response.output_item.added","output_index":1,"item":{"type":"message","id":"msg_01","role":"assistant","status":"in_progress","content":[]}}` + "\n\n",
 		"event: response.output_text.delta\n" +
 			`data: {"type":"response.output_text.delta","output_index":1,"content_index":0,"delta":"Here are the results."}` + "\n\n",
+		"event: response.output_text.annotation.added\n" +
+			`data: {"type":"response.output_text.annotation.added","annotation":{"type":"url_citation","url":"https://example.com/ai-news","title":"Latest AI News","start_index":0,"end_index":21},"annotation_index":0,"content_index":0,"item_id":"msg_01","output_index":1,"sequence_number":10}` + "\n\n",
+		"event: response.output_text.annotation.added\n" +
+			`data: {"type":"response.output_text.annotation.added","annotation":{"type":"url_citation","url":"https://example.com/more-news","title":"More AI News","start_index":22,"end_index":40},"annotation_index":1,"content_index":0,"item_id":"msg_01","output_index":1,"sequence_number":11}` + "\n\n",
 		"event: response.output_item.done\n" +
-			`data: {"type":"response.output_item.done","output_index":1,"item":{"type":"message","id":"msg_01","role":"assistant","status":"completed","content":[{"type":"output_text","text":"Here are the results.","annotations":[{"type":"url_citation","url":"https://example.com/ai-news","title":"Latest AI News","start_index":0,"end_index":21}]}]}}` + "\n\n",
+			`data: {"type":"response.output_item.done","output_index":1,"item":{"type":"message","id":"msg_01","role":"assistant","status":"completed","content":[{"type":"output_text","text":"Here are the results.","annotations":[{"type":"url_citation","url":"https://example.com/ai-news","title":"Latest AI News","start_index":0,"end_index":21},{"type":"url_citation","url":"https://example.com/more-news","title":"More AI News","start_index":22,"end_index":40}]}]}}` + "\n\n",
 		"event: response.completed\n" +
 			`data: {"type":"response.completed","response":{"id":"resp_01","status":"completed","output":[],"usage":{"input_tokens":100,"output_tokens":50,"total_tokens":150}}}` + "\n\n",
 	}
@@ -4090,6 +4094,7 @@ func TestResponsesStream_WebSearchResponse(t *testing.T) {
 		toolCalls       []fantasy.StreamPart
 		toolResults     []fantasy.StreamPart
 		textDeltas      []fantasy.StreamPart
+		sources         []fantasy.StreamPart
 		finishes        []fantasy.StreamPart
 	)
 	for _, p := range parts {
@@ -4102,6 +4107,8 @@ func TestResponsesStream_WebSearchResponse(t *testing.T) {
 			toolResults = append(toolResults, p)
 		case fantasy.StreamPartTypeTextDelta:
 			textDeltas = append(textDeltas, p)
+		case fantasy.StreamPartTypeSource:
+			sources = append(sources, p)
 		case fantasy.StreamPartTypeFinish:
 			finishes = append(finishes, p)
 		}
@@ -4123,6 +4130,16 @@ func TestResponsesStream_WebSearchResponse(t *testing.T) {
 	require.NotEmpty(t, textDeltas, "should have text deltas")
 	require.Equal(t, "Here are the results.", textDeltas[0].Delta)
 
+	require.Len(t, sources, 2, "should have two source citations from annotation events")
+	require.Equal(t, fantasy.SourceTypeURL, sources[0].SourceType)
+	require.Equal(t, "https://example.com/ai-news", sources[0].URL)
+	require.Equal(t, "Latest AI News", sources[0].Title)
+	require.NotEmpty(t, sources[0].ID, "source should have an ID")
+	require.Equal(t, fantasy.SourceTypeURL, sources[1].SourceType)
+	require.Equal(t, "https://example.com/more-news", sources[1].URL)
+	require.Equal(t, "More AI News", sources[1].Title)
+	require.NotEmpty(t, sources[1].ID, "source should have an ID")
+
 	require.Len(t, finishes, 1)
 	responsesMeta, ok := finishes[0].ProviderMetadata[Name].(*ResponsesProviderMetadata)
 	require.True(t, ok)

providers/openai/responses_language_model.go

@@ -1077,18 +1077,54 @@ func (o responsesLanguageModel) Stream(ctx context.Context, call fantasy.Call) (
 					}
 				}
 
-			case "response.output_text.delta":
-				textDelta := event.AsResponseOutputTextDelta()
-				if !yield(fantasy.StreamPart{
-					Type:  fantasy.StreamPartTypeTextDelta,
-					ID:    textDelta.ItemID,
-					Delta: textDelta.Delta,
-				}) {
-					return
-				}
+				case "response.output_text.delta":
+					textDelta := event.AsResponseOutputTextDelta()
+					if !yield(fantasy.StreamPart{
+						Type:  fantasy.StreamPartTypeTextDelta,
+						ID:    textDelta.ItemID,
+						Delta: textDelta.Delta,
+					}) {
+						return
+					}
+
+				case "response.output_text.annotation.added":
+					added := event.AsResponseOutputTextAnnotationAdded()
+					// The Annotation field is typed as `any` in the SDK;
+					// it deserializes as map[string]interface{} from JSON.
+					annotationMap, ok := added.Annotation.(map[string]interface{})
+					if !ok {
+						break
+					}
+					annotationType, _ := annotationMap["type"].(string)
+					switch annotationType {
+					case "url_citation":
+						url, _ := annotationMap["url"].(string)
+						title, _ := annotationMap["title"].(string)
+						if !yield(fantasy.StreamPart{
+							Type:       fantasy.StreamPartTypeSource,
+							ID:         uuid.NewString(),
+							SourceType: fantasy.SourceTypeURL,
+							URL:        url,
+							Title:      title,
+						}) {
+							return
+						}
+					case "file_citation":
+						title := "Document"
+						if fn, ok := annotationMap["filename"].(string); ok && fn != "" {
+							title = fn
+						}
+						if !yield(fantasy.StreamPart{
+							Type:       fantasy.StreamPartTypeSource,
+							ID:         uuid.NewString(),
+							SourceType: fantasy.SourceTypeDocument,
+							Title:      title,
+						}) {
+							return
+						}
+						}
 
-			case "response.reasoning_summary_part.added":
-				added := event.AsResponseReasoningSummaryPartAdded()
+				case "response.reasoning_summary_part.added":				added := event.AsResponseReasoningSummaryPartAdded()
 				state := activeReasoning[added.ItemID]
 				if state != nil {
 					state.metadata.Summary = append(state.metadata.Summary, "")