refactor(auto-thumbnail): [PKG-AUTO-THUMB-03] own hidden renderers and reject stale seeks

scripts/generate-auto-thumbnail-fixture.mjs

@@ -0,0 +1,48 @@
+import assert from 'node:assert/strict'
+import { execFileSync } from 'node:child_process'
+import fs from 'node:fs'
+import path from 'node:path'
+import process from 'node:process'
+import { hash } from '../refactor/scripts/releases.mjs'
+
+const output = path.resolve(process.argv[2] || 'refactor/.cache/auto-thumbnail-fixture')
+assert(!fs.existsSync(output), 'Use a new directory; never overwrite frozen media')
+const ffmpeg = process.env.ARTPLAYER_FFMPEG || 'ffmpeg'
+const version = execFileSync(ffmpeg, ['-version'], { encoding: 'utf8' }).split(/\r?\n/)[0]
+fs.mkdirSync(output, { recursive: true })
+const segments = [['purple', '0.033333333'], ['red', '1.966666667'], ['black', '2'], ['blue', '2'], ['yellow', '2']]
+const args = [
+  '-hide_banner',
+  '-loglevel',
+  'error',
+  '-n',
+  ...segments.flatMap(([color, duration]) => ['-f', 'lavfi', '-i', `color=c=${color}:s=320x180:r=30:d=${duration}`]),
+  '-filter_complex',
+  '[0:v][1:v][2:v][3:v][4:v]concat=n=5:v=1:a=0[v]',
+  '-map',
+  '[v]',
+  '-c:v',
+  'libx264',
+  '-pix_fmt',
+  'yuv420p',
+  '-g',
+  '30',
+  '-movflags',
+  '+faststart',
+  'auto-thumbnail-timeline.mp4',
+]
+execFileSync(ffmpeg, args, { cwd: output, stdio: 'pipe', timeout: 120000 })
+const bytes = fs.readFileSync(path.join(output, 'auto-thumbnail-timeline.mp4'))
+fs.writeFileSync(path.join(output, 'manifest.json'), `${JSON.stringify({
+  kind: 'generated-auto-thumbnail-timeline',
+  version,
+  args,
+  width: 320,
+  height: 180,
+  fps: 30,
+  duration: 8,
+  segments,
+  purpose: 'Unique purple first frame, then red/black/blue/yellow timeline; distinguish missing transparent pixels, legitimate black frames and stale first frames.',
+  file: { name: 'auto-thumbnail-timeline.mp4', bytes: bytes.length, sha256: hash(bytes) },
+}, null, 2)}\n`)
+console.log(`Generated auto-thumbnail timeline in ${output}`)