Split prompts into pre/prompt/post and tidy the AIGen video form.

Keep wrappers off the library mid-prompt so Use as input and Extend restore the same split, send stills to xAIGen as hidden inputs, and stop the two-column library from growing with the list.

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

server/api/generate.post.ts

@@ -5,6 +5,7 @@ import type { LoraStackItem } from '~/utils/loras'
 import { clampVideoCfg } from '~/utils/generationPresets'
 import { defaultVideoSteps, isLtxWorkflow, isTextToVideo, LTX_DISABLED_MESSAGE, ltxWorkflowEnabled, parseVideoWorkflow, videoEngineOf } from '~/utils/videoModels'
 import { allowIdentityRefs, normalizePermanenceRefs, resolveGlobalLocks, type PermanenceRef } from '~/utils/globalLocks'
+import { composePromptParts } from '~/utils/promptParts'
 
 function parseDuration(raw: unknown) {
   const seconds = Number(raw)
@@ -137,11 +138,13 @@ export default defineEventHandler(async (event) => {
   if (!image && !textToVideo) {
     throw createError({ statusCode: 400, statusMessage: 'An initial image is required' })
   }
-  const promptRaw = (fields.prompt || '').trim()
-  if (!promptRaw) {
+  const promptMid = (fields.prompt || '').trim()
+  const promptPre = (fields.promptPre || '').trim()
+  const promptPost = (fields.promptPost || '').trim()
+  if (!composePromptParts(promptPre, promptMid, promptPost)) {
     throw createError({ statusCode: 400, statusMessage: 'A motion prompt is required' })
   }
-  const resolvedLocks = resolveGlobalLocks(fields.globalLocks || '', promptRaw)
+  const resolvedLocks = resolveGlobalLocks(fields.globalLocks || '', promptMid)
   const prompt = resolvedLocks.prompt
   const globalLocks = resolvedLocks.locks
   const extensions = parseExtensions(fields.extensions)
@@ -243,6 +246,9 @@ export default defineEventHandler(async (event) => {
     familyId,
     payload: {
       prompt,
+      promptMid: promptMid || undefined,
+      promptPre: promptPre || undefined,
+      promptPost: promptPost || undefined,
       name: clipName,
       folderId,
       aspect: fields.aspect || 'auto',