Add Prompt Builder page for multi-scene prompt sequences.

Name, save, and load ordered scenes on the server; assemble copyable text with a Batch-compatible double blank line between scenes.

server/utils/promptSequences.ts

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+import { existsSync, mkdirSync, readFileSync, renameSync, writeFileSync } from 'node:fs'
+import { join } from 'node:path'
+import { ownerRoot } from '~/server/utils/library'
+import {
+  normalizePromptSequence,
+  normalizePromptSequenceName,
+  normalizeScene,
+  emptyScene,
+  type PromptSequence,
+  type PromptSequenceScene
+} from '~/utils/promptSequences'
+
+const writeChains = new Map<string, Promise<unknown>>()
+
+function sequencesPath(owner: string) {
+  return join(ownerRoot(owner), 'prompt-sequences.json')
+}
+
+function ensureOwner(owner: string) {
+  mkdirSync(ownerRoot(owner), { recursive: true })
+}
+
+function readSequences(owner: string): PromptSequence[] {
+  ensureOwner(owner)
+  const path = sequencesPath(owner)
+  if (!existsSync(path)) return []
+  try {
+    const parsed = JSON.parse(readFileSync(path, 'utf8'))
+    return Array.isArray(parsed)
+      ? parsed.map(normalizePromptSequence).filter((item): item is PromptSequence => Boolean(item))
+      : []
+  } catch {
+    return []
+  }
+}
+
+function writeSequences(owner: string, sequences: PromptSequence[]) {
+  ensureOwner(owner)
+  const path = sequencesPath(owner)
+  const tmp = `${path}.tmp`
+  writeFileSync(tmp, JSON.stringify(sequences, null, 2))
+  renameSync(tmp, path)
+}
+
+function mutate<T>(owner: string, fn: (sequences: PromptSequence[]) => T): Promise<T> {
+  const prev = writeChains.get(owner) || Promise.resolve()
+  const run = prev.then(() => {
+    const sequences = readSequences(owner)
+    const result = fn(sequences)
+    writeSequences(owner, sequences)
+    return result
+  })
+  writeChains.set(owner, run.then(() => undefined, () => undefined))
+  return run
+}
+
+function normalizeScenesInput(raw: unknown): PromptSequenceScene[] {
+  if (!Array.isArray(raw) || !raw.length) return [emptyScene(1)]
+  return raw.map((scene, index) => normalizeScene(scene, index))
+}
+
+export function listPromptSequences(owner: string) {
+  return readSequences(owner).sort((a, b) => b.updatedAt - a.updatedAt || a.name.localeCompare(b.name))
+}
+
+export function getPromptSequence(owner: string, id: string) {
+  const wanted = String(id || '').trim()
+  const sequence = readSequences(owner).find(item => item.id === wanted)
+  if (!sequence) throw createError({ statusCode: 404, statusMessage: 'Sequence not found' })
+  return sequence
+}
+
+export async function savePromptSequence(owner: string, input: {
+  name: string
+  scenes?: unknown
+  overwrite?: boolean
+}) {
+  const name = normalizePromptSequenceName(input.name)
+  if (!name) throw createError({ statusCode: 400, statusMessage: 'A sequence name is required' })
+  const scenes = normalizeScenesInput(input.scenes)
+  const now = Date.now()
+  return mutate(owner, (sequences) => {
+    const existing = sequences.find(item => item.name.toLowerCase() === name.toLowerCase())
+    if (existing && !input.overwrite) {
+      throw createError({ statusCode: 409, statusMessage: `Overwrite sequence “${existing.name}”?` })
+    }
+    if (existing) {
+      existing.scenes = scenes
+      existing.updatedAt = now
+      return existing
+    }
+    const created: PromptSequence = {
+      id: crypto.randomUUID(),
+      name,
+      scenes,
+      createdAt: now,
+      updatedAt: now
+    }
+    sequences.unshift(created)
+    return created
+  })
+}
+
+export async function updatePromptSequence(owner: string, id: string, input: {
+  name?: string
+  scenes?: unknown
+}) {
+  const wanted = String(id || '').trim()
+  if (!wanted) throw createError({ statusCode: 400, statusMessage: 'Missing sequence id' })
+  return mutate(owner, (sequences) => {
+    const existing = sequences.find(item => item.id === wanted)
+    if (!existing) throw createError({ statusCode: 404, statusMessage: 'Sequence not found' })
+    if (input.name !== undefined) {
+      const name = normalizePromptSequenceName(input.name)
+      if (!name) throw createError({ statusCode: 400, statusMessage: 'A sequence name is required' })
+      const clash = sequences.find(item => item.id !== wanted && item.name.toLowerCase() === name.toLowerCase())
+      if (clash) throw createError({ statusCode: 409, statusMessage: `A sequence named “${clash.name}” already exists` })
+      existing.name = name
+    }
+    if (input.scenes !== undefined) {
+      existing.scenes = normalizeScenesInput(input.scenes)
+    }
+    existing.updatedAt = Date.now()
+    return existing
+  })
+}
+
+export async function deletePromptSequence(owner: string, id: string) {
+  const wanted = String(id || '').trim()
+  if (!wanted) throw createError({ statusCode: 400, statusMessage: 'Missing sequence id' })
+  return mutate(owner, (sequences) => {
+    const index = sequences.findIndex(item => item.id === wanted)
+    if (index < 0) throw createError({ statusCode: 404, statusMessage: 'Sequence not found' })
+    const [removed] = sequences.splice(index, 1)
+    return removed
+  })
+}