Record the Path disclosure ruling, and a script to reclaim the disk

[maximsan]

Why

Two records, both about work that was invisible until it bit.

#599 shipped a deliberate departure from prototype/disclosure.jsx: every
module a learner can reach carries a caret and opens and shuts, where the
design pins the active one open with no caret. That ruling lived only in a
merged PR body. ADR-0024 records it.

Separately, the machine ran out of disk mid-branch — 163 MB free of 460 GB,
enough that commands could not write their own output. An iOS Flutter build
never reclaims what it takes, and nothing in the repo said so or offered a way
out. tool/clean_build_caches.sh does both.

Watch for

• The design doc is where the ADR earns its keep.
  07-components.md still states the
  prototype's formula as the spec, and that paragraph is what someone reads
  while porting the screen — docs/adr/ is not. The warning goes there, next
  to the sentence it contradicts.
• path_density.dart gains one clause, citing the ADR the way three files
  nearby cite ADR-0016. No behaviour changes, hence no-changelog: One disclosure draws every expandable section #599
  already logged what a learner sees.
• The script deletes only what it can name. safe_rm is an allow-list of
  four paths, not a "stay inside this tree" test — the looser version I wrote
  first would have permitted ~/Library/Developer/Xcode/Archives, which the
  header promises it never touches. Source, Archives and ~/.pub-cache are
  refused; simulators are pruned with delete unavailable, never erase.
• It reports and exits unless given --apply, and --worktrees is a
  second opt-in because wiping a live worktree's build/ forces a rebuild on
  whoever is using it.
• The number is 0024 by the README's rule — the next one on origin/main.
  A concurrent session is drafting its own 0024 for the pricing arms; whichever
  lands second renumbers, as docs/adr/README.md says.

Checks

adr_numbering_test passes: 0001–0024, no gaps, heading matches filename.
Both new links resolve. The script was run from inside a worktree, where it
correctly resolved the main checkout and listed all six build/ directories;
its path guard was exercised against eight paths, allowing four and refusing
lib/, Documents, Archives, .pub-cache and /.