RotateWALFiles used a non-blocking send (select/default) on rotation
channels buffered at 64. With thousands of nodes and few shards, the
channel fills instantly and nearly all hosts are skipped, leaving WAL
files unrotated indefinitely.
Replace with a blocking send using a shared 2-minute deadline so the
checkpoint goroutine waits for the staging goroutine to drain the
channel instead of immediately giving up.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Entire-Checkpoint: a1ec897216fa
WAL writes now go through bufio.Writer instead of raw syscalls per record,
reducing I/O overhead. Buffers are flushed on rotate, drain, and shutdown.
Fixed misleading MemoryCap comment ("Max bytes" → "Max memory in GB").
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Entire-Checkpoint: b38dc35e5334
