Method persist

packages/db/src/buffers/session-buffer.ts:344–370

* Atomic write-back: session blob + wallclock ZSET + projects SET + * profile index + ClickHouse buffer rows + counter. * * No TTLs on the blob or profile index — they are removed exclusively by * `cleanup()` after `session_end` emission. This guarantees the reaper * can always find a

(
    current: IClickhouseSession,
    chRows: IClickhouseSession[]
  )

   * has been down.
   */
  private async persist(
    current: IClickhouseSession,
    chRows: IClickhouseSession[]
  ) {
    const projectId = current.project_id;
    const deviceId = current.device_id;
    const wallClockMs = Date.now();

    const multi = this.redis.multi();
    multi.set(sessionKey(projectId, deviceId), JSON.stringify(current));
    multi.zadd(wallclockSetKey(projectId), wallClockMs.toString(), deviceId);
    multi.sadd(PROJECTS_SET_KEY, projectId);

    if (current.profile_id && current.profile_id !== current.device_id) {
      multi.set(profileIndexKey(projectId, current.profile_id), deviceId);
    }

    for (const row of chRows) {
      multi.rpush(this.redisKey, JSON.stringify(row));
    }
    await multi.exec();

    const bufferLength = await this.getBufferSize();
    if (bufferLength >= this.batchSize) {
      await this.tryFlush();
    }
  }

  /**
   * Squash the (sign=-1, sign=+1) rows for each session id down to the