feat: publish sanitized custom.97 source

relay/common/response_model_guard.go

@@ -32,6 +32,7 @@ type ResponseGuardUsage struct {
 }
 
 type ResponseGuardAttempt struct {
+	Timing     *UpstreamTiming    `json:"-"`
 	OnEvent    func([]byte, bool) `json:"-"`
 	OnClose    func()             `json:"-"`
 	closeOnce  sync.Once
@@ -141,6 +142,9 @@ func (g *ResponseModelGuard) APIError() *types.NewAPIError {
 
 // Only read the provider's declaration and numeric usage, never generated text.
 func (a *ResponseGuardAttempt) observe(payload []byte, stream bool) error {
+	if stream {
+		a.Timing.Mark("first_sse_data")
+	}
 	if a.OnEvent != nil {
 		a.OnEvent(payload, stream)
 	}