fix: extract reasoning_content from DMR streaming responses

pkg/model/provider/oaistream/adapter.go

@@ -5,6 +5,7 @@ This is a shared adapter for OpenAI-compatible streams.
 */
 
 import (
+	"encoding/json"
 	"io"
 
 	"github.com/openai/openai-go/v3"
@@ -66,13 +67,24 @@ func (a *StreamAdapter) Recv() (chat.MessageStreamResponse, error) {
 			a.lastFinishReason = finishReason
 		}
 
+		// Extract reasoning_content from ExtraFields since the OpenAI SDK
+		// does not yet have a dedicated field for it. Providers like DMR
+		// send reasoning tokens as a "reasoning_content" JSON field in the
+		// chat completion chunk delta.
+		var reasoningContent string
+		if ef, ok := choice.Delta.JSON.ExtraFields["reasoning_content"]; ok && ef.Raw() != "" {
+			// ef.Raw() returns the raw JSON value (e.g. `"some text"`), so
+			// we unmarshal it to get the plain Go string.
+			_ = json.Unmarshal([]byte(ef.Raw()), &reasoningContent)
+		}
+
 		response.Choices[i] = chat.MessageStreamChoice{
 			Index:        int(choice.Index),
 			FinishReason: finishReason,
 			Delta: chat.MessageDelta{
-				Role:    choice.Delta.Role,
-				Content: choice.Delta.Content,
-				// ReasoningContent not available in this SDK version
+				Role:             choice.Delta.Role,
+				Content:          choice.Delta.Content,
+				ReasoningContent: reasoningContent,
 			},
 		}
 

pkg/model/provider/oaistream/adapter_test.go

@@ -0,0 +1,103 @@
+package oaistream
+
+import (
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/openai/openai-go/v3"
+	"github.com/openai/openai-go/v3/packages/ssestream"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// newTestStream creates an SSE stream from raw SSE event data served by a test HTTP server.
+func newTestStream(t *testing.T, sseData string) *ssestream.Stream[openai.ChatCompletionChunk] {
+	t.Helper()
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.Header().Set("Content-Type", "text/event-stream")
+		_, _ = w.Write([]byte(sseData))
+	}))
+	t.Cleanup(srv.Close)
+
+	resp, err := http.Get(srv.URL) //nolint:gosec,bodyclose // body is closed by the stream
+	require.NoError(t, err)
+	return ssestream.NewStream[openai.ChatCompletionChunk](ssestream.NewDecoder(resp), nil)
+}
+
+func TestStreamAdapter_ReasoningContent(t *testing.T) {
+	t.Parallel()
+
+	// Simulate SSE events with reasoning_content field in the delta,
+	// as sent by DMR for reasoning models.
+	sseData := `data: {"id":"c1","object":"chat.completion.chunk","created":1,"model":"test","choices":[{"index":0,"delta":{"role":"assistant","reasoning_content":"Let me think"},"finish_reason":null}]}
+
+data: {"id":"c1","object":"chat.completion.chunk","created":1,"model":"test","choices":[{"index":0,"delta":{"reasoning_content":" about this"},"finish_reason":null}]}
+
+data: {"id":"c1","object":"chat.completion.chunk","created":1,"model":"test","choices":[{"index":0,"delta":{"content":"Hello!"},"finish_reason":null}]}
+
+data: {"id":"c1","object":"chat.completion.chunk","created":1,"model":"test","choices":[{"index":0,"delta":{},"finish_reason":"stop"}]}
+
+data: [DONE]
+
+`
+
+	stream := newTestStream(t, sseData)
+	adapter := NewStreamAdapter(stream, false)
+	defer adapter.Close()
+
+	// First chunk: reasoning content "Let me think"
+	resp, err := adapter.Recv()
+	require.NoError(t, err)
+	require.Len(t, resp.Choices, 1)
+	assert.Equal(t, "Let me think", resp.Choices[0].Delta.ReasoningContent)
+	assert.Empty(t, resp.Choices[0].Delta.Content)
+
+	// Second chunk: reasoning content " about this"
+	resp, err = adapter.Recv()
+	require.NoError(t, err)
+	require.Len(t, resp.Choices, 1)
+	assert.Equal(t, " about this", resp.Choices[0].Delta.ReasoningContent)
+	assert.Empty(t, resp.Choices[0].Delta.Content)
+
+	// Third chunk: regular content "Hello!"
+	resp, err = adapter.Recv()
+	require.NoError(t, err)
+	require.Len(t, resp.Choices, 1)
+	assert.Equal(t, "Hello!", resp.Choices[0].Delta.Content)
+	assert.Empty(t, resp.Choices[0].Delta.ReasoningContent)
+
+	// Fourth chunk: finish reason stop
+	resp, err = adapter.Recv()
+	require.NoError(t, err)
+	require.Len(t, resp.Choices, 1)
+	assert.Equal(t, "stop", string(resp.Choices[0].FinishReason))
+
+	// Stream done
+	_, err = adapter.Recv()
+	assert.ErrorIs(t, err, io.EOF)
+}
+
+func TestStreamAdapter_NoReasoningContent(t *testing.T) {
+	t.Parallel()
+
+	// Simulate a normal stream without reasoning_content.
+	sseData := `data: {"id":"c1","object":"chat.completion.chunk","created":1,"model":"test","choices":[{"index":0,"delta":{"role":"assistant","content":"Hi"},"finish_reason":null}]}
+
+data: {"id":"c1","object":"chat.completion.chunk","created":1,"model":"test","choices":[{"index":0,"delta":{},"finish_reason":"stop"}]}
+
+data: [DONE]
+
+`
+
+	stream := newTestStream(t, sseData)
+	adapter := NewStreamAdapter(stream, false)
+	defer adapter.Close()
+
+	resp, err := adapter.Recv()
+	require.NoError(t, err)
+	require.Len(t, resp.Choices, 1)
+	assert.Equal(t, "Hi", resp.Choices[0].Delta.Content)
+	assert.Empty(t, resp.Choices[0].Delta.ReasoningContent)
+}