Propagate model through streamed responses

StreamAccumulator never set its model field, so
Response().Model was always empty for streamed
completions. Add a Model field to stream events
and populate it in all three providers (OpenAI,
Anthropic, Bedrock).

Signed-off-by: Bryan Frimin <bryan@getprobo.com>

pkg/llm/anthropic/provider.go

@@ -431,15 +431,16 @@ func (s *anthropicStream) mapStreamEvent(event *anthropic.MessageStreamEventUnio
 		return evt, true
 
 	case "message_start":
-		if event.Message.Usage.InputTokens > 0 {
-			return llm.ChatCompletionStreamEvent{
-				Usage: &llm.Usage{
-					InputTokens:  int(event.Message.Usage.InputTokens),
-					OutputTokens: int(event.Message.Usage.OutputTokens),
-				},
-			}, true
+		evt := llm.ChatCompletionStreamEvent{
+			Model: string(event.Message.Model),
 		}
-		return llm.ChatCompletionStreamEvent{}, false
+		if event.Message.Usage.InputTokens > 0 || event.Message.Usage.OutputTokens > 0 {
+			evt.Usage = &llm.Usage{
+				InputTokens:  int(event.Message.Usage.InputTokens),
+				OutputTokens: int(event.Message.Usage.OutputTokens),
+			}
+		}
+		return evt, true
 
 	default:
 		return llm.ChatCompletionStreamEvent{}, false

pkg/llm/bedrock/provider.go

@@ -83,7 +83,7 @@ func (p *Provider) ChatCompletionStream(ctx context.Context, req *llm.ChatComple
 		return nil, mapError(err)
 	}
 
-	return newBedrockStream(output.GetStream()), nil
+	return newBedrockStream(output.GetStream(), req.Model), nil
 }
 
 func buildInput(req *llm.ChatCompletionRequest) *bedrockruntime.ConverseInput {
@@ -346,14 +346,17 @@ type bedrockStream struct {
 	events      <-chan types.ConverseStreamOutput
 	current     llm.ChatCompletionStreamEvent
 	err         error
+	model       string
+	modelSent   bool
 	toolIndex   int
 	inToolUse   bool
 }
 
-func newBedrockStream(eventStream *bedrockruntime.ConverseStreamEventStream) *bedrockStream {
+func newBedrockStream(eventStream *bedrockruntime.ConverseStreamEventStream, model string) *bedrockStream {
 	return &bedrockStream{
 		eventStream: eventStream,
 		events:      eventStream.Events(),
+		model:       model,
 	}
 }
 
@@ -361,6 +364,10 @@ func (s *bedrockStream) Next() bool {
 	for event := range s.events {
 		mapped, ok := s.mapEvent(event)
 		if ok {
+			if !s.modelSent {
+				mapped.Model = s.model
+				s.modelSent = true
+			}
 			s.current = mapped
 			return true
 		}

pkg/llm/chat.go

@@ -90,6 +90,7 @@ type (
 	}
 
 	ChatCompletionStreamEvent struct {
+		Model        string        // present on first event if provider supports it
 		Delta        MessageDelta
 		Usage        *Usage        // present on final event if provider supports it
 		FinishReason *FinishReason // present on final event
@@ -206,6 +207,10 @@ func (a *StreamAccumulator) Response() *ChatCompletionResponse {
 }
 
 func (a *StreamAccumulator) accumulate(event ChatCompletionStreamEvent) {
+	if a.model == "" && event.Model != "" {
+		a.model = event.Model
+	}
+
 	a.content.WriteString(event.Delta.Content)
 
 	for _, tcd := range event.Delta.ToolCalls {

pkg/llm/llm_test.go

@@ -508,7 +508,7 @@ func TestStreamAccumulator(t *testing.T) {
 		t.Parallel()
 
 		events := []llm.ChatCompletionStreamEvent{
-			{Delta: llm.MessageDelta{Content: "Hello"}},
+			{Model: "gpt-4o", Delta: llm.MessageDelta{Content: "Hello"}},
 			{Delta: llm.MessageDelta{Content: " world"}},
 			{Delta: llm.MessageDelta{
 				ToolCalls: []llm.ToolCallDelta{
@@ -537,6 +537,7 @@ func TestStreamAccumulator(t *testing.T) {
 		require.NoError(t, acc.Err())
 
 		resp := acc.Response()
+		assert.Equal(t, "gpt-4o", resp.Model)
 		assert.Equal(t, "Hello world", resp.Message.Text())
 		assert.Equal(t, llm.RoleAssistant, resp.Message.Role)
 		assert.Equal(t, llm.FinishReasonToolCalls, resp.FinishReason)

pkg/llm/openai/provider.go

@@ -181,9 +181,13 @@ func buildMessages(messages []llm.Message) []openai.ChatCompletionMessageParamUn
 				case llm.TextPart:
 					parts = append(parts, openai.TextContentPart(p.Text))
 				case llm.ImagePart:
-					parts = append(parts, openai.ImageContentPart(openai.ChatCompletionContentPartImageImageURLParam{
-						URL: p.URL,
-					}))
+					parts = append(
+						parts,
+						openai.ImageContentPart(openai.ChatCompletionContentPartImageImageURLParam{
+							URL: p.URL,
+						},
+						),
+					)
 				}
 			}
 			out = append(out, openai.UserMessage(parts))
@@ -408,7 +412,9 @@ func (s *openaiStream) Close() error {
 }
 
 func mapChunkToEvent(chunk *openai.ChatCompletionChunk) llm.ChatCompletionStreamEvent {
-	event := llm.ChatCompletionStreamEvent{}
+	event := llm.ChatCompletionStreamEvent{
+		Model: chunk.Model,
+	}
 
 	if chunk.Usage.PromptTokens > 0 || chunk.Usage.CompletionTokens > 0 {
 		usage := llm.Usage{