fed-prims: Phase D — CIDv1 (multihash + base32 multibase), pure OCaml, canonical IPFS vectors

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

plans/fed-sx-host-primitives.md

@@ -93,7 +93,7 @@ check** → tests → commit → tick box → Progress-log line → push.
   appendix-A vectors + a "reordered dict keys → identical bytes" determinism test.
 - **Acceptance:** vectors + round-trip + determinism pass; WASM links.
 
-### Phase D — CID computation, pure OCaml
+### Phase D — CID computation, pure OCaml ✅ DONE
 - Multihash (sha2-256 = 0x12, sha3-256 = 0x16; varint code + varint len + digest).
 - CIDv1 = `0x01 || codec-varint || multihash`. Codecs: dag-cbor 0x71, raw 0x55.
 - Multibase base32 lower (`b` prefix, RFC 4648 no-pad).
@@ -205,6 +205,13 @@ printf '(epoch 1)\n(crypto-sha256 "abc")\n' | \
 
 _Newest first._
 
+- 2026-05-18 — Phase D: pure-OCaml `lib/sx_cid.ml` (unsigned-varint,
+  multihash, CIDv1, multibase base32-lower), primitives `cid-from-bytes`
+  / `cid-from-sx` (cbor→sha2-256→mh→cidv1, dag-cbor codec 0x71). 5 tests:
+  raw "abc"=bafkreif2pall7d…, raw ""=bafkreihdwdcefg…, dag-cbor {}=
+  bafyreigbtj4x7i… (all match canonical IPFS CIDs; no `ipfs` CLI so
+  vectors independently derived in Python), key-order determinism. WASM
+  boot green with new lib module; Erlang 530/530; run_tests +5.
 - 2026-05-18 — Phase C: pure-OCaml `lib/sx_cbor.ml` (dag-cbor encode/
   decode), primitives `cbor-encode`/`cbor-decode`. RFC 8949 Appendix-A
   vectors, length-then-bytewise key sort + order-invariance determinism,