fix

apps/api/internal/processing/openai.go

@@ -243,10 +243,7 @@ type chatResponse struct {
 		CompletionTokens int `json:"completion_tokens"`
 		TotalTokens      int `json:"total_tokens"`
 	} `json:"usage"`
-	Error *struct {
-		Message string `json:"message"`
-		Type    string `json:"type"`
-	} `json:"error"`
+	Error *openAIErrorBody `json:"error"`
 }
 
 var (
@@ -466,8 +463,13 @@ func (c *OpenAIClient) doEmbed(ctx context.Context, texts []string) ([][]float32
 }
 
 func (c *OpenAIClient) doComplete(ctx context.Context, system, user string, temperature float64, maxTokens int, reasoningEffort string) (Completion, bool, error) {
+	sysRole := "system"
+	if openAIReasoningChatModel(c.Model) {
+		// GPT-5 family prefers developer over system on Chat Completions.
+		sysRole = "developer"
+	}
 	reqBody := buildChatCompletionBody(c.Model, []chatMessage{
-		{Role: "system", Content: system},
+		{Role: sysRole, Content: system},
 		{Role: "user", Content: user},
 	}, temperature, maxTokens, reasoningEffort)
 	body, err := json.Marshal(reqBody)
@@ -502,19 +504,13 @@ func (c *OpenAIClient) doComplete(ctx context.Context, system, user string, temp
 		return Completion{}, false, decErr
 	}
 	if res.StatusCode == http.StatusTooManyRequests || res.StatusCode >= 500 {
-		msg := "rate limited or server error"
-		if parsed.Error != nil && parsed.Error.Message != "" {
-			msg = TruncateError(errors.New(parsed.Error.Message))
-		}
+		msg := formatOpenAIHTTPError(res.StatusCode, parsed.Error)
 		httpErr := errors.New(msg)
 		stopWait(httpErr)
 		return Completion{}, true, httpErr
 	}
 	if res.StatusCode >= 400 {
-		msg := fmt.Sprintf("openai http %d", res.StatusCode)
-		if parsed.Error != nil && parsed.Error.Message != "" {
-			msg = TruncateError(errors.New(parsed.Error.Message))
-		}
+		msg := formatOpenAIHTTPError(res.StatusCode, parsed.Error)
 		httpErr := errors.New(msg)
 		stopWait(httpErr)
 		return Completion{}, false, httpErr