export-legacy-refs --from-pastes <app>: each paste row's own object (pastes.object_id), keyed legacy:<app>:paste:<slug>, also when the object is filed under another legacy name (screenshots that were also avatars)

ddiff --git a/scripts/export-legacy-refs.js b/scripts/export-legacy-refs.js
iindex 34454f8..99d20f7 100644
---- a/scripts/export-legacy-refs.js
++++ b/scripts/export-legacy-refs.js
@@@ -6,6 +6,11 @@
   * scripts/migrate-screenshot-refs.js there).
   *
   *   node scripts/export-legacy-refs.js --prefix legacy:live:paste: --out /tmp/refs.json [--db ./data/media.db]
++ *   node scripts/export-legacy-refs.js --from-pastes live --out /tmp/paste-refs.json
++ *
++ * --from-pastes <app> answers for every paste row of the app that names its object (pastes.object_id), keyed
++ * `legacy:<app>:paste:<slug>`: the paste's own record of its bytes, also when the object was filed under
++ * another legacy name (a screenshot that was also an avatar is `legacy:<app>:avatar:<slug>`).
   *
   * Read-only (opens the database readonly). Output: { generated_at, prefix, count, objects: [{ legacy_ref, id,
   * kind, lifecycle_status }] } ordered by legacy_ref. Deleted objects are included with their status, so the
@@@ -18,12 +23,20 @@ const Database = require('better-sqlite3');
  const args = process.argv.slice(2);
  const arg = (name, dflt) => { const i = args.indexOf(`--${name}`); return i >= 0 ? args[i + 1] : dflt; };
  const prefix = arg('prefix');
++const fromPastes = arg('from-pastes');
  const out = arg('out');
  const dbPath = path.resolve(arg('db', process.env.DB_PATH || './data/media.db'));
--if (!prefix || !/^legacy:[a-z0-9_-]+:/.test(prefix) || !out) { console.error('usage: export-legacy-refs.js --prefix legacy:<app>:<kind>: --out <file> [--db path]'); process.exit(2); }
++if (!out || (!fromPastes && !/^legacy:[a-z0-9_-]+:/.test(String(prefix || ''))) || (fromPastes && !/^[a-z0-9_-]+$/.test(fromPastes))) {
++    console.error('usage: export-legacy-refs.js (--prefix legacy:<app>:<kind>: | --from-pastes <app>) --out <file> [--db path]');
++    process.exit(2);
++}
  
  const db = new Database(dbPath, { readonly: true, fileMustExist: true });
--const objects = db.prepare(`SELECT legacy_ref, id, kind, lifecycle_status FROM media_objects
--                            WHERE legacy_ref >= ? AND legacy_ref < ? ORDER BY legacy_ref`).all(prefix, `${prefix}￿`);
--fs.writeFileSync(out, JSON.stringify({ generated_at: new Date().toISOString(), prefix, count: objects.length, objects }, null, 1));
--console.log(`[export-legacy-refs] ${objects.length} object(s) under ${prefix} → ${out}`);
++const objects = fromPastes
++    ? db.prepare(`SELECT 'legacy:' || p.app_id || ':paste:' || p.slug AS legacy_ref, o.id, o.kind, o.lifecycle_status
++                  FROM pastes p JOIN media_objects o ON o.id = p.object_id WHERE p.app_id = ? ORDER BY p.slug`).all(fromPastes)
++    : db.prepare(`SELECT legacy_ref, id, kind, lifecycle_status FROM media_objects
++                  WHERE legacy_ref >= ? AND legacy_ref < ? ORDER BY legacy_ref`).all(prefix, `${prefix}￿`);
++const label = fromPastes ? `${fromPastes} paste rows` : prefix;
++fs.writeFileSync(out, JSON.stringify({ generated_at: new Date().toISOString(), prefix: prefix || null, from_pastes: fromPastes || null, count: objects.length, objects }, null, 1));
++console.log(`[export-legacy-refs] ${objects.length} object(s) from ${label} -> ${out}`);