The pattern behind issue #22 came back once already (removed in v1.57.2,
back with the icon rail in v1.58.0). tools/check_structure.mjs now fails
on any :has() in the web stylesheets whose argument matches [style...],
pointing at the line; AGENTS.md, docs/guides/testing.md and lessons.md
say why and what to do instead (a class on an ancestor).
Prepared in a cloud session (checkpoint cbfc782), committed now that the
issue #22 fix is on this branch.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>