erlang: wire cid:from_bytes/1 + cid:to_string/1 against cid-from-bytes/cid-from-sx (Phase 8, +7 ffi tests)

lib/erlang/runtime.sx

@@ -1559,6 +1559,8 @@
     (er-register-bif! "file" "delete" 1 er-bif-file-delete)
     ;; Phase 8 FFI — host-primitive BIFs (loops/fed-prims)
     (er-register-pure-bif! "crypto" "hash" 2 er-bif-crypto-hash)
+    (er-register-pure-bif! "cid" "from_bytes" 1 er-bif-cid-from-bytes)
+    (er-register-pure-bif! "cid" "to_string" 1 er-bif-cid-to-string)
     (er-mk-atom "ok")))
 
 ;; Register everything at load time.

lib/erlang/tests/ffi.sx

@@ -106,9 +106,39 @@
   "ok")
 
 (er-ffi-test
-  "cid:from_bytes unregistered"
-  (er-lookup-bif "cid" "from_bytes" 1)
-  nil)
+  "cid:from_bytes is_binary"
+  (ffi-nm (ffi-ev "is_binary(cid:from_bytes(<<97,98,99>>))"))
+  "true")
+
+(er-ffi-test
+  "cid:from_bytes deterministic"
+  (ffi-nm (ffi-ev "cid:from_bytes(<<97,98,99>>) =:= cid:from_bytes(<<97,98,99>>)"))
+  "true")
+
+(er-ffi-test
+  "cid:from_bytes distinct inputs distinct CIDs"
+  (ffi-nm (ffi-ev "cid:from_bytes(<<97,98,99>>) =/= cid:from_bytes(<<97,98,100>>)"))
+  "true")
+
+(er-ffi-test
+  "cid:from_bytes non-binary -> error:badarg"
+  (ffi-nm (ffi-ev "try cid:from_bytes(42) catch error:badarg -> ok end"))
+  "ok")
+
+(er-ffi-test
+  "cid:to_string is_binary"
+  (ffi-nm (ffi-ev "is_binary(cid:to_string({ok, 42}))"))
+  "true")
+
+(er-ffi-test
+  "cid:to_string deterministic"
+  (ffi-nm (ffi-ev "cid:to_string(foo) =:= cid:to_string(foo)"))
+  "true")
+
+(er-ffi-test
+  "cid:to_string distinct terms distinct CIDs"
+  (ffi-nm (ffi-ev "cid:to_string(foo) =/= cid:to_string(bar)"))
+  "true")
 
 (er-ffi-test
   "file:list_dir unregistered"