Covers the case where df unchanged after rm -rf or cargo clean because
sanoid snapshots captured the deleted files. Documents the vacuum
procedure: identify holding snapshots, destroy them to reclaim space
immediately, or use sanoid --prune-snapshots for the gentler path.
Updates Pitfalls to acknowledge this as the exception to "never touch
sanoid-managed snaps."
Discovered 2026-06-24: cargo clean freed 5.5G but df showed 16G unchanged.
usedbysnapshots = 26.6G across 9 sanoid snapshots. Full vacuum freed 13G
(16G → 29G free, pool 80% → 72%).
Discovered 2026-06-22: zroot/home/clawdie was missing from sanoid config,
allowing 10 autosnaps from April to accumulate 23.6G of dead weight.
Skill covers: pool/dataset audit, sanoid coverage check, safe destroy
of orphaned snapshots, template reference, and pitfall avoidance.
