- wo_hkdf_sha256_extract/expand (RFC 5869) + expand_label (RFC 8446 §7.1),
internal C over the existing hmac_sha256; SHA-256 (mandatory-suite hash;
SHA-384 a later add for the AES-256 suite)
- no builtin, no compiler change -- no .wo consumer yet (the TLS handshake
is the consumer); exposed for the C unit test
- KAT-gated in test_crypto: RFC 5869 Test Case 1 (PRK + 42-byte OKM) and
three HKDF-Expand-Label vectors (key/iv/derived-secret shape); 57/0,
ASan/UBSan clean; runtime battery green
- rv2 9 ladder: A (AEAD, = rv2 8) and B (HKDF) now done; next C X25519
(cherry picked from commit c8d27b6c89a80cd97a996ff7d8b64ff4895e4b26)