Disk reduction — reclaim space from Rust build residue

The dev Mac has a 1.8 TiB data volume that fills with Rust build output. Measured 2026-08-14: the volume hit 340 MiB free — every agent tool call failed ENOSPC before it could run — and a sweep took it to 189 GiB without deleting one line of source.

Most of this now prunes itself. scripts/target-gc.sh runs hourly from every rust-build.sh build: orphaned buckets go after a day, anything idle 14 days goes, and a low-disk pressure pass (under 100 GiB free) collects idle state aggressively while sparing the newest. make target-gc shows what it would take right now. The manual sweeps below remain the tool for IMMEDIATE reclaim — the collector never touches a dir written within 2h, never the newest rlib seed, never nub-dev's bucket — and for the families it does not scan (merged worktree checkouts).

Judge every reclaim by df, never du. scripts/rust-build.sh CoW-clones buckets with cp -c, so APFS bills the same physical blocks to every referencing path. Summed du sizes overstate what you get back — measured, a set of buckets du called 135 G returned 73 GiB of df. A du -sh over ~/.cache/nub also takes minutes; df is instant.

df -h /System/Volumes/Data

Where the space actually is

Ranked by what a sweep returns, with the measured 2026-08-14 figures: