Serve the stage from a 1600px preview instead of the grid thumb.

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

server/api/library/stills/[id]/preview.get.ts

@@ -0,0 +1,30 @@
+import { existsSync, createReadStream } from 'node:fs'
+import { fileEtag, stillPath, stillPreviewPath, existingStillPreviewPath } from '~/server/utils/library'
+
+export default defineEventHandler((event) => {
+  const { owner } = assertLibraryOwner(event)
+  const id = String(getRouterParam(event, 'id') || '')
+  const still = getStill(owner, id)
+  assertFolderAccess(event, still.folderId)
+
+  const path = existingStillPreviewPath(owner, id)
+  const original = stillPath(owner, still.id)
+  // Ready preview → stream. Never await ffmpeg; never stream the archive master.
+  if (path && existsSync(path) && path !== original) {
+    const etag = fileEtag(path)
+    setHeader(event, 'ETag', etag)
+    setHeader(event, 'Cache-Control', 'public, max-age=86400')
+    if (getHeader(event, 'if-none-match') === etag) {
+      setResponseStatus(event, 304)
+      return null
+    }
+    setHeader(event, 'Content-Type', 'image/jpeg')
+    return sendStream(event, createReadStream(path))
+  }
+
+  // Missing → answer now; build .preview.jpg in the background
+  void stillPreviewPath(owner, id).catch(() => null)
+  setHeader(event, 'Cache-Control', 'no-store')
+  setResponseStatus(event, 204)
+  return null
+})