fed-prims: Phase A — SHA-256 + SHA-512, pure OCaml, 7 NIST vectors

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

plans/fed-sx-host-primitives.md

@@ -68,7 +68,7 @@ Errors: `raise (Eval_error "name: shape")`. Byte strings are OCaml `string`
 Dependency order. Each phase: implement → `dune build` (ocaml) → **WASM build
 check** → tests → commit → tick box → Progress-log line → push.
 
-### Phase A — SHA-2 (sha256 + sha512), pure OCaml
+### Phase A — SHA-2 (sha256 + sha512), pure OCaml ✅ DONE
 - New `lib/sx_sha2.ml` (or inline in primitives if small): SHA-256 + SHA-512.
 - Primitives `crypto-sha256`, `crypto-sha512` → lowercase hex string.
 - Tests (`bin/run_tests.ml` or a dedicated `bin/test_crypto.ml`): NIST vectors —
@@ -205,7 +205,10 @@ printf '(epoch 1)\n(crypto-sha256 "abc")\n' | \
 
 _Newest first._
 
-- (none yet — Phase A is first)
+- 2026-05-18 — Phase A: pure-OCaml `lib/sx_sha2.ml` (SHA-256 + SHA-512),
+  primitives `crypto-sha256`/`crypto-sha512`. 7 NIST FIPS 180-4 vectors pass
+  (empty/abc/896-bit/1M-'a' for sha256; empty/abc/896-bit for sha512). WASM
+  boot green with new lib module; Erlang conformance 530/530 unchanged.
 
 ## Blockers