Stop ghost extension clips and recover last-frame extract after an interrupt.

Only one Comfy finish path can save a clip, hide catalog entries whose MP4 is missing, and retry last-frame extract so a truncated file does not dump FFmpeg noise into the UI.

Co-authored-by: Cursor <cursoragent@cursor.com>

server/api/generate.post.ts

@@ -403,7 +403,14 @@ async function runGeneration(
     assertJobActive(job)
 
     copyFileSync(currentPath, part1Path)
-    await extractLastFrame(part1Path, framePath)
+    try {
+      await extractLastFrame(part1Path, framePath)
+    } catch (error) {
+      const detail = error instanceof Error ? error.message : String(error)
+      throw new Error(detail.includes('last frame')
+        ? detail
+        : `Could not extract the last frame for the next extension: ${detail}`)
+    }
     const frame = readFileSync(framePath)
     job.library.extendPart1Path = part1Path
     job.library.prompt = ext.prompt