Group extension chains in the library and add shot-script queues.

Keep every saved segment, show the longest clip with an expand list, branch on extend, and parse shot 2/3 blocks into a shared-duration queue with live part status.

server/api/extend.post.ts

@@ -97,7 +97,10 @@ export default defineEventHandler(async (event) => {
     duration: durationSeconds,
     extendTmpDir: tmpDir,
     extendPart1Path: part1Path,
-    extendSourceClipId: source.id
+    extendSourceClipId: source.id,
+    familyId: crypto.randomUUID(),
+    parentClipId: source.id,
+    chainIndex: (source.chainIndex || 0) + 1
   }
 
   emitJob(job, { type: 'status', message: 'Extracting last frame & stitching extension...', progress: 2 })
@@ -226,7 +229,10 @@ async function runExtend(
       imageName: job.library.imageName,
       imageSubfolder: job.library.imageSubfolder,
       extendTmpDir: job.library.extendTmpDir,
-      extendPart1Path: job.library.extendPart1Path
+      extendPart1Path: job.library.extendPart1Path,
+      familyId: job.library.familyId,
+      parentClipId: job.library.parentClipId,
+      chainIndex: job.library.chainIndex
     })
   }
   emitJob(job, { type: 'status', message: 'Job queued on ComfyUI', progress: 8 })