feat(api, xai): integrate xAI Grok image models and extend API endpoints for image support

- Added new xAI Grok image models (`grok-imagine-image`, `grok-imagine-image-quality`) with high-fidelity and aspect ratio configurations.
- Extended `isSupportedImagesModel` logic to validate xAI models.
- Implemented API request builders for image generation/editing with customizable options (e.g., resolution, aspect ratio, response format).
- Enhanced `/v1/images` endpoints to handle xAI model capabilities, including response normalization and model-specific handlers.
- Updated unit tests to validate xAI model validation, request structure, and API integration.

internal/runtime/executor/xai_executor.go

@@ -27,6 +27,13 @@ import (
 
 var xaiDataTag = []byte("data:")
 
+const (
+	xaiImageHandlerType         = "openai-image"
+	xaiImagesGenerationsPath    = "/images/generations"
+	xaiImagesEditsPath          = "/images/edits"
+	xaiDefaultImageEndpointPath = xaiImagesGenerationsPath
+)
+
 // XAIExecutor is a stateless executor for xAI Grok's Responses API.
 type XAIExecutor struct {
 	cfg *config.Config
@@ -76,6 +83,10 @@ func (e *XAIExecutor) HttpRequest(ctx context.Context, auth *cliproxyauth.Auth,
 }
 
 func (e *XAIExecutor) Execute(ctx context.Context, auth *cliproxyauth.Auth, req cliproxyexecutor.Request, opts cliproxyexecutor.Options) (resp cliproxyexecutor.Response, err error) {
+	if endpointPath := xaiImageEndpointPath(opts); endpointPath != "" {
+		return e.executeImages(ctx, auth, req, endpointPath)
+	}
+
 	token, baseURL := xaiCreds(auth)
 	if baseURL == "" {
 		baseURL = xaiauth.DefaultAPIBaseURL
@@ -151,6 +162,51 @@ func (e *XAIExecutor) Execute(ctx context.Context, auth *cliproxyauth.Auth, req
 	return resp, statusErr{code: http.StatusRequestTimeout, msg: "xai stream error: stream disconnected before response.completed"}
 }
 
+func (e *XAIExecutor) executeImages(ctx context.Context, auth *cliproxyauth.Auth, req cliproxyexecutor.Request, endpointPath string) (resp cliproxyexecutor.Response, err error) {
+	token, baseURL := xaiCreds(auth)
+	if baseURL == "" {
+		baseURL = xaiauth.DefaultAPIBaseURL
+	}
+	if endpointPath == "" {
+		endpointPath = xaiDefaultImageEndpointPath
+	}
+
+	url := strings.TrimSuffix(baseURL, "/") + endpointPath
+	httpReq, err := http.NewRequestWithContext(ctx, http.MethodPost, url, bytes.NewReader(req.Payload))
+	if err != nil {
+		return resp, err
+	}
+	applyXAIHeaders(httpReq, auth, token, false, "")
+	e.recordXAIRequest(ctx, auth, url, httpReq.Header.Clone(), req.Payload)
+
+	httpClient := helps.NewProxyAwareHTTPClient(ctx, e.cfg, auth, 0)
+	httpResp, err := httpClient.Do(httpReq)
+	if err != nil {
+		helps.RecordAPIResponseError(ctx, e.cfg, err)
+		return resp, err
+	}
+	defer func() {
+		if errClose := httpResp.Body.Close(); errClose != nil {
+			log.Errorf("xai executor: close response body error: %v", errClose)
+		}
+	}()
+	helps.RecordAPIResponseMetadata(ctx, e.cfg, httpResp.StatusCode, httpResp.Header.Clone())
+
+	data, err := io.ReadAll(httpResp.Body)
+	if err != nil {
+		helps.RecordAPIResponseError(ctx, e.cfg, err)
+		return resp, err
+	}
+	helps.AppendAPIResponseChunk(ctx, e.cfg, data)
+
+	if httpResp.StatusCode < 200 || httpResp.StatusCode >= 300 {
+		helps.LogWithRequestID(ctx).Debugf("request error, error status: %d, error message: %s", httpResp.StatusCode, helps.SummarizeErrorBody(httpResp.Header.Get("Content-Type"), data))
+		return resp, statusErr{code: httpResp.StatusCode, msg: string(data)}
+	}
+
+	return cliproxyexecutor.Response{Payload: data, Headers: httpResp.Header.Clone()}, nil
+}
+
 func (e *XAIExecutor) ExecuteStream(ctx context.Context, auth *cliproxyauth.Auth, req cliproxyexecutor.Request, opts cliproxyexecutor.Options) (_ *cliproxyexecutor.StreamResult, err error) {
 	token, baseURL := xaiCreds(auth)
 	if baseURL == "" {
@@ -454,6 +510,21 @@ func xaiExecutionSessionID(req cliproxyexecutor.Request, opts cliproxyexecutor.O
 	return ""
 }
 
+func xaiImageEndpointPath(opts cliproxyexecutor.Options) string {
+	if opts.SourceFormat.String() != xaiImageHandlerType {
+		return ""
+	}
+
+	path := xaiMetadataString(opts.Metadata, cliproxyexecutor.RequestPathMetadataKey)
+	if strings.HasSuffix(path, "/images/edits") {
+		return xaiImagesEditsPath
+	}
+	if strings.HasSuffix(path, "/images/generations") {
+		return xaiImagesGenerationsPath
+	}
+	return xaiDefaultImageEndpointPath
+}
+
 func xaiMetadataString(meta map[string]any, key string) string {
 	if len(meta) == 0 || key == "" {
 		return ""