permissionsFor carries a caveat that its Set cannot represent a narrow deny
under a broad grant, so callers must gate with decide(). Now that
permissionMatches is also public, the wrong composition is directly reachable
and looks idiomatic - and the warning lived only on the other half of it.
Adds the pointer to permissionMatches, and covers scopeKey and safeRecord in
the exports test, which the brief omitted.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>