Keep extension chains alive and save each finished segment.

The overall bar made a long queue look stuck at ~9% during the first clip, and nothing was written until the last step. Save checkpoints, use per-step progress, and stop treating a short Comfy history lag as a dropped job.

server/utils/comfy.ts

@@ -209,25 +209,27 @@ export async function isComfyPromptDropped(promptId: string) {
   if (queue.running > 0 || queue.pending > 0) return false
   const history = await fetchHistory(promptId)
   const entry = history?.[promptId] as { status?: { status_str?: string; completed?: boolean } } | undefined
-  if (!entry) return true
+  if (!entry) return false
   const inspected = inspectHistory(history, promptId)
   if (inspected.video) return false
   const status = entry.status?.status_str
   if (status === 'error' || status === 'interrupted') return true
   if (entry.status?.completed) return true
-  return true
+  return false
 }
 
 export function inspectHistory(history: Record<string, unknown> | null, promptId: string) {
   const video = extractVideo(history, promptId)
+  if (video) return { video, completed: true, error: null as string | null }
   if (!history) return { video: null, completed: false, error: null as string | null }
   const entry = (history[promptId] || history) as {
     status?: { status_str?: string; completed?: boolean }
   }
-  const error = entry?.status?.status_str === 'error' || entry?.status?.status_str === 'interrupted'
-    ? (entry.status.status_str === 'interrupted' ? 'Job interrupted.' : 'ComfyUI reported an execution error')
-    : null
-  return { video, completed: Boolean(video), error }
+  const status = entry?.status?.status_str
+  if (status === 'interrupted') return { video: null, completed: false, error: 'Job interrupted.' }
+  if (status === 'error') return { video: null, completed: false, error: 'ComfyUI reported an execution error' }
+  if (entry?.status?.completed) return { video: null, completed: true, error: 'ComfyUI finished without an MP4' }
+  return { video: null, completed: false, error: null as string | null }
 }
 
 export async function probeComfy() {