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>

utils/promptParts.ts

@@ -0,0 +1,42 @@
+export type PromptParts = {
+  pre: string
+  prompt: string
+  post: string
+}
+
+export function sanitizePromptPart(raw: unknown) {
+  return String(raw || '').replace(/\r\n/g, '\n').replace(/\r/g, '')
+}
+
+export function composePromptParts(pre: string, prompt: string, post: string) {
+  return [pre, prompt, post]
+    .map(part => sanitizePromptPart(part).trim())
+    .filter(Boolean)
+    .join('\n\n')
+}
+
+export function applyPromptParts(parts: PromptParts, middle: string) {
+  return composePromptParts(parts.pre, middle, parts.post)
+}
+
+export function restorePromptParts(saved: string, stored?: Partial<PromptParts> | null, current?: Partial<PromptParts> | null): PromptParts {
+  const pre = sanitizePromptPart(stored?.pre ?? '').trim()
+  const post = sanitizePromptPart(stored?.post ?? '').trim()
+  if (pre || post) {
+    return {
+      pre,
+      prompt: sanitizePromptPart(stored?.prompt ?? saved).trim() || sanitizePromptPart(saved).trim(),
+      post
+    }
+  }
+  let mid = sanitizePromptPart(stored?.prompt ?? saved)
+  const curPre = sanitizePromptPart(current?.pre || '').trim()
+  const curPost = sanitizePromptPart(current?.post || '').trim()
+  if (curPre && mid.startsWith(curPre)) mid = mid.slice(curPre.length).replace(/^\n+/, '')
+  if (curPost && mid.endsWith(curPost)) mid = mid.slice(0, Math.max(0, mid.length - curPost.length)).replace(/\n+$/, '')
+  return {
+    pre: current?.pre || '',
+    prompt: mid.trim(),
+    post: current?.post || ''
+  }
+}