feat(executor): add logging for resolved xAI base URL and enhance test coverage

- Introduced `logXAIResolvedBaseURL` for consistent logging of resolved upstream base URLs.
- Added helper `xaiBaseURLSource` to classify base URL origins (default, CLI chat proxy, custom).
- Enhanced test suite with `TestXAIBaseURLSource` to cover base URL source classification logic.

internal/runtime/executor/xai_executor.go

@@ -131,6 +131,7 @@ func (e *XAIExecutor) Execute(ctx context.Context, auth *cliproxyauth.Auth, req
 
 	token, _ := xaiCreds(auth)
 	baseURL := xaiChatBaseURL(auth)
+	logXAIResolvedBaseURL(ctx, baseURL)
 
 	prepared, err := e.prepareResponsesRequest(ctx, req, opts, true)
 	if err != nil {
@@ -220,6 +221,7 @@ func (e *XAIExecutor) executeCompact(ctx context.Context, auth *cliproxyauth.Aut
 func (e *XAIExecutor) executeCompactRequest(ctx context.Context, auth *cliproxyauth.Auth, req cliproxyexecutor.Request, opts cliproxyexecutor.Options) (*xaiPreparedRequest, []byte, http.Header, error) {
 	token, _ := xaiCreds(auth)
 	baseURL := xaiChatBaseURL(auth)
+	logXAIResolvedBaseURL(ctx, baseURL)
 
 	prepared, err := e.prepareResponsesRequestTo(ctx, req, opts, false, sdktranslator.FormatOpenAIResponse)
 	if err != nil {
@@ -470,6 +472,7 @@ func (e *XAIExecutor) executeImages(ctx context.Context, auth *cliproxyauth.Auth
 	if baseURL == "" {
 		baseURL = xaiauth.DefaultAPIBaseURL
 	}
+	logXAIResolvedBaseURL(ctx, baseURL)
 	if endpointPath == "" {
 		endpointPath = xaiDefaultImageEndpointPath
 	}
@@ -515,6 +518,7 @@ func (e *XAIExecutor) executeVideos(ctx context.Context, auth *cliproxyauth.Auth
 	if baseURL == "" {
 		baseURL = xaiauth.DefaultAPIBaseURL
 	}
+	logXAIResolvedBaseURL(ctx, baseURL)
 
 	method := http.MethodPost
 	endpointPath := xaiVideosGenerationsPath
@@ -585,6 +589,7 @@ func (e *XAIExecutor) ExecuteStream(ctx context.Context, auth *cliproxyauth.Auth
 
 	token, _ := xaiCreds(auth)
 	baseURL := xaiChatBaseURL(auth)
+	logXAIResolvedBaseURL(ctx, baseURL)
 
 	prepared, err := e.prepareResponsesRequest(ctx, req, opts, true)
 	if err != nil {
@@ -985,6 +990,23 @@ func xaiIsCLIChatProxyBaseURL(baseURL string) bool {
 	return xaiNormalizeBaseURL(baseURL) == xaiNormalizeBaseURL(xaiauth.CLIChatProxyBaseURL)
 }
 
+// xaiBaseURLSource classifies a resolved xAI base URL for logging.
+func xaiBaseURLSource(baseURL string) string {
+	switch {
+	case xaiIsDefaultAPIBaseURL(baseURL):
+		return "DefaultAPIBaseURL"
+	case xaiIsCLIChatProxyBaseURL(baseURL):
+		return "CLIChatProxyBaseURL"
+	default:
+		return "custom"
+	}
+}
+
+// logXAIResolvedBaseURL emits a console log for the resolved upstream base URL.
+func logXAIResolvedBaseURL(ctx context.Context, baseURL string) {
+	helps.LogWithRequestID(ctx).Infof("xai: using base_url=%s source=%s", baseURL, xaiBaseURLSource(baseURL))
+}
+
 func applyXAIHeaders(r *http.Request, auth *cliproxyauth.Auth, token string, stream bool, sessionID string) {
 	applyXAIDefaultHeaders(r, token, stream, sessionID)
 	applyXAICustomHeaders(r, auth)

internal/runtime/executor/xai_executor_test.go

@@ -1573,6 +1573,28 @@ func TestXAIExecutorReasoningReplayCacheReplaysFunctionCallForClaudeToolResult(t
 	}
 }
 
+func TestXAIBaseURLSource(t *testing.T) {
+	tests := []struct {
+		name    string
+		baseURL string
+		want    string
+	}{
+		{name: "default api", baseURL: xaiauth.DefaultAPIBaseURL, want: "DefaultAPIBaseURL"},
+		{name: "default api trailing slash", baseURL: xaiauth.DefaultAPIBaseURL + "/", want: "DefaultAPIBaseURL"},
+		{name: "cli chat proxy", baseURL: xaiauth.CLIChatProxyBaseURL, want: "CLIChatProxyBaseURL"},
+		{name: "cli chat proxy trailing slash", baseURL: xaiauth.CLIChatProxyBaseURL + "/", want: "CLIChatProxyBaseURL"},
+		{name: "custom", baseURL: "https://gateway.example.com/v1", want: "custom"},
+		{name: "empty treated as custom", baseURL: "", want: "custom"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := xaiBaseURLSource(tt.baseURL); got != tt.want {
+				t.Fatalf("xaiBaseURLSource(%q) = %q, want %q", tt.baseURL, got, tt.want)
+			}
+		})
+	}
+}
+
 func TestXAIChatBaseURL(t *testing.T) {
 	tests := []struct {
 		name string