Redis hash tags don’t make KEYS cheap

// before: blocks Redis while it walks every key in the database
const cycles = await redis.keys(`{${runId}}:wp:*`);
// after: read the counter the writer already keeps, then check existence in one round trip
const high = Number((await redis.hget(`{${runId}}:seq`, "c")) ?? 0);
const keys = Array.from({ length: high }, (_, i) => `{${runId}}:wp:${i + 1}`);
const p = redis.pipeline(); keys.forEach((k) => p.exists(k));
const found = (await p.exec())!.map(([, n], i) => (n ? keys[i] : null)).filter(Boolean);