Layer 5: replace two priv_post references in author-direct fast path
with the correct per-V_x CEK + priv_x lookup. Cache/prefilter logic
unchanged.
Layer 3: replace the "partially superseded" warning banner with a
plain scope note explaining the Mode 1/Mode 2 distinction reduces to
"body encrypted vs body plaintext"; wrap-slot canonical form lives in
Layer 2.
Layer 6: mark as superseded by Layer 4. README updated to match.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>