fix: improve OpenAI error body capture and log request body on 400

- Use resp.Body() instead of resp.RawBody() for non-streaming error responses
- Fall back to RawBody() for streaming responses
- Log the full request body on API errors for debugging

internal/providers/openai.go

@@ -72,11 +72,14 @@ func (p *OpenAIProvider) ChatCompletion(ctx context.Context, req *models.Unified
 	if !resp.IsSuccess() {
 		msg := resp.String()
 		if msg == "" {
-			if body, err := io.ReadAll(resp.RawBody()); err == nil {
-				msg = string(body)
+			if b := resp.Body(); len(b) > 0 {
+				msg = string(b)
 			}
 		}
+		// Log the request body for debugging
+		reqJSON, _ := json.Marshal(body)
 		log.Printf("OpenAI API Error (%d): %s", resp.StatusCode(), msg)
+		log.Printf("OpenAI request body: %s", string(reqJSON))
 		return nil, fmt.Errorf("OpenAI API error (%d): %s", resp.StatusCode(), msg)
 	}
 
@@ -182,11 +185,18 @@ func (p *OpenAIProvider) ChatCompletionStream(ctx context.Context, req *models.U
 	if !resp.IsSuccess() {
 		msg := resp.String()
 		if msg == "" {
-			if body, err := io.ReadAll(resp.RawBody()); err == nil {
-				msg = string(body)
+			if b := resp.Body(); len(b) > 0 {
+				msg = string(b)
+			}
+			if msg == "" {
+				if b, err := io.ReadAll(resp.RawBody()); err == nil {
+					msg = string(b)
+				}
 			}
 		}
+		reqJSON, _ := json.Marshal(body)
 		log.Printf("OpenAI API Error (%d): %s", resp.StatusCode(), msg)
+		log.Printf("OpenAI request body: %s", string(reqJSON))
 		return nil, fmt.Errorf("OpenAI API error (%d): %s", resp.StatusCode(), msg)
 	}