修复问题6

server.js

@@ -91,6 +91,7 @@ const createS3Client = (credentials) => {
 const progressMap = {};
 const transcodeProcesses = new Map();
 const wsSubscriptions = new Map();
+const progressApiLogMap = new Map();
 
 const AVAILABLE_VIDEO_ENCODERS = [
     { value: 'h264_rkmpp', label: 'h264_rkmpp (RKMPP H.264)' },
@@ -822,6 +823,16 @@ app.get('/api/progress', (req, res) => {
 
         const progressKey = getProgressKey(key);
         const progress = progressMap[progressKey] || null;
+        const observedState = progress
+            ? `${progress.status}:${typeof progress.percent === 'number' ? progress.percent : 'na'}`
+            : 'null';
+        if (progressApiLogMap.get(progressKey) !== observedState) {
+            progressApiLogMap.set(progressKey, observedState);
+            console.log(`[progress-api] key=${key} status=${progress?.status || 'null'} percent=${typeof progress?.percent === 'number' ? progress.percent : 'na'}`);
+        }
+        res.setHeader('Cache-Control', 'no-store, no-cache, must-revalidate, proxy-revalidate');
+        res.setHeader('Pragma', 'no-cache');
+        res.setHeader('Expires', '0');
         res.json({ progress });
     } catch (error) {
         console.error('Error fetching progress:', error);