通过直接压缩的 All-NULL 租户 — mark_invalid 永远不会触发

-- Found by: commit 038822925 agent -- Location: tsl/src/continuous_aggs/insert.c:632-639, 712-718

-- When every row has a NULL tenant, the buffer is empty so the foreach loop over hypertable_ids never executes. tenant_buffer_unencodable is set but mark_invalid never fires. Correctness maintained via seqnum=0 fallback, but the code path is unusual.