* storage/topology: keep disk-full read-only volumes vacuumable
The vacuum sweep skipped every read-only replica, so a volume that went
read-only because its disk filled could never reclaim its garbage — the
exact situation compaction exists for. The volume server now reports
disk_space_low in VacuumVolumeCheckResponse, and the sweep skips a
read-only replica only when the flag is clear. An explicit volumeId
vacuum is unaffected: it already bypassed the read-only rule.
The field takes number 4: 2 and 3 are downstream-allocated for tombstone
retention, keeping the wire merge clean.
Generated with [Devin](https://devin.ai)
Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>
* storage: measure vacuum free space against live bytes
The pre-compaction space check required the current .dat + .idx size
free, which includes the garbage being reclaimed — on a nearly full disk
that estimate can never fit, so the volume stayed garbage-bound forever.
Measure against the estimated compacted output instead: superblock plus
live index entries plus live content bytes, with the existing ten
percent buffer unchanged. Mirrors the same check in the Rust volume
server.
Generated with [Devin](https://devin.ai)
Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>
* vacuum: count per-needle framing in the compacted-size estimate
The live-bytes estimate covered each live needle's content and index
entry but not its .dat framing (header, checksum, timestamp, padding —
~32 bytes on version 3). For small-needle volumes that is more than the
10% headroom, so a disk with space between the estimate and the real
output still ran out mid-compaction. Rust side mirrors the same formula.
Generated with [Devin](https://devin.ai)
Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>
* storage: report disk_space_low only when it is the sole read-only cause
Review feedback (ihnokim, greptile, devin): a volume read-only for low
disk space AND an operator mark or I/O quarantine was still eligible for
the automatic sweep, rewriting a copy meant to stay protected. The flag
now reports only the benign sole-cause case in both servers.
Generated with [Devin](https://devin.ai)
Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>
* topology: fail closed when the read-only lookup misses in the sweep
A heartbeat can drop the volume from the DataNode cache between the
location-list copy and VacuumVolumeCheck; a lookup error previously
skipped the read-only check entirely. Review feedback (coderabbit).
Generated with [Devin](https://devin.ai)
Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>
---------
Co-authored-by: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>
0978e7f833