docs(scripts): spell out the sweep that measures this scanner, and what it missed

The header pointed at "the sweep" without saying how to run one. It now names
the corpus, the parser and the comparison, so the 16-file census is
re-derivable from the file itself rather than from a PR description.

Also records the result that ranks the two instruments: deleting the `{`
counting inside `${...}` passed every pinned case AND the whole 4,739-file
sweep, because the tree does not happen to write that shape. The case that
holds it now was written from the mutation, not from the corpus.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DdCnBGcHeufjrq7drTD3wt

Author: claude

scripts/js-comment-mask.mjs

@@ -51,19 +51,27 @@
  * afternoon proving the sentence it quoted meant the opposite.
  *
  * This header used to state that as a property -- "cannot fabricate a lead".
- * It was not one. Measured on 2026-08-21 (#10427) by diffing this scan's mask
- * against `@typescript-eslint/parser`'s comment ranges over 4,733 files: 16
- * disagreed, and 15 of them in the FABRICATES direction, up to 10,252 comment
- * bytes handed to a caller as live code in a single file. The cause was the
- * template scan above; the same sweep after the fix disagrees on 0 files.
+ * It was not one. Measured on 2026-08-21 (#10427): walk every
+ * `.{ts,tsx,mts,cts,js,mjs,cjs,jsx}` file in the tree (minus `node_modules`,
+ * `dist`, `.next`, `build`, `.turbo`, `coverage`), parse each with
+ * `@typescript-eslint/parser` (`{ comment: true, range: true }`), and diff the
+ * comment ranges it reports against this scan's `comment` array byte for byte.
+ * Over 4,739 files, 16 disagreed -- 15 in the FABRICATES direction, up to
+ * 10,252 comment bytes handed to a caller as live code in a single file. The
+ * cause was the template scan above; the same sweep after the fix disagrees on
+ * 0 files.
  *
  * The lesson is about the claim, not the bug. A failure DIRECTION is a
  * property of an implementation, not of an intention, and this one cannot be
  * read off the code -- it took an independent parser over the whole tree to
  * find out which way the module actually failed. So the honest statement is
- * the one that can be re-derived: the shapes below are pinned, the sweep that
- * measured them is the way to check the rest, and neither direction is
- * promised by construction. Re-run it after touching `scanSource`.
+ * the one that can be re-derived: the shapes below are pinned, the sweep just
+ * described is the way to check the rest, and neither direction is promised by
+ * construction. Re-run it after touching `scanSource` -- and note that the
+ * sweep is the STRONGER instrument of the two. A mutation that deleted the
+ * brace counting inside `${...}` passed every case below AND the whole sweep,
+ * because the tree did not happen to write the shape; the case that now holds
+ * it was written from the mutation, not from the corpus.
  */
 
 /** A character that can end an identifier -- i.e. a value, so `/` is division. */