Pins existing BLOCK rules in the two pre-* executor hooks so a future
silent weakening of BLOCK_RULES surfaces as test failures instead of
slipping through code review.
50 new tests covering both hooks plus allow-list pins (lib/, tests/,
docs/, ls, git, npm) and fail-open on malformed input. Reuses
tests/helpers/hook-helper.mjs child-process spawner.
[skip-docs]
