§H.12 step 16: block-acl.4th policy capsule -- Phase 5 (BMAPFMT) complete

capsules/block-acl.4th (blocks 4019-4020, next free range per
BLOCK_MAP.md): BLK-ACL-CHECK (block# -- allow?), a real fast-deny check
mirroring vm.c:611-624's pattern for blocks instead of words. First
touch lazily claims the block (allow=1, TTL=256, same base as ACL.4th's
own), matching the word card's default-permissive baseline. Not a stub --
genuinely does something on every call.

Loaded via a new EXEC line in init.4th right after ACL.4th's own;
confirmed ACL.4th's own activation is unaffected. Passed mkcapsule
--lint. Live-tested via QMP keystrokes: 1 BLK-ACL-CHECK executed cleanly.

Phase 5 (BMAPFMT) is now fully complete -- field layout, flags bits, C
accessors, FORTH wrappers, and a real policy word.

Verified 3-arch boot to ok> (amd64/aarch64/riscv64).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

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