恢复无 cookie 拉流修复：iPhone 原生播放器（AVPlayer/夸克系统解码）不携带 cookie 时媒体资产可凭会话 ID 拉流，纯 HTTP 生效；新增拉流拒绝诊断日志

internal/app/ui_playback.go

@@ -94,6 +94,17 @@ func (app *UIApp) registerPlaybackRoutes(mux *http.ServeMux) {
 	mux.HandleFunc("/api/ui/playback/progress", app.handlePlaybackProgress)
 }
 
+// recordPlaybackAssetDenial 记录媒体资产请求被拒的情况，便于诊断
+// iOS/WebKit 原生媒体管线的拉流失败（区分会话失效与观看者不匹配）。
+func (app *UIApp) recordPlaybackAssetDenial(request *http.Request, reason string) {
+	agent := request.UserAgent()
+	if len(agent) > 120 {
+		agent = agent[:120]
+	}
+	app.downloader.recordDiagnostic(diagnosticEvent{Level: "warn", Event: "playback.asset.denied",
+		HTTPStatus: http.StatusGone, Message: reason + " ua=" + agent})
+}
+
 func playbackRequestAllowed(writer http.ResponseWriter, request *http.Request, method string) bool {
 	writer.Header().Set("Cache-Control", "private, no-store, no-transform")
 	writer.Header().Set("X-Accel-Buffering", "no")