Add bounded structured crypto operations

site/doc/areas/noise.txt

@@ -14,6 +14,7 @@ hmac_sha256
 hmac_sha256_hex
 random_bytes
 crypto_equal
+crypto_operation
 password_hash
 password_verify
 password_needs_rehash

site/doc/pages/crypto_operation.txt

@@ -0,0 +1,28 @@
+:sig
+DValue crypto_operation(DValue request)
+
+:params
+request : structured operation, algorithm, and operation-specific fields
+return value : map with ok, bounded error code, and operation-specific output
+
+:content
+Runs one explicitly supported structured asymmetric cryptographic operation. The initial allowlist is `key_generate` with `ES256` and `jwt_sign` with `ES256`. Unknown operations and algorithms fail closed.
+
+ES256 signing validates that `x`, `y`, and `d` form one P-256 key, forces the protected `alg` to `ES256`, and emits a compact JWT with a 64-byte JOSE signature. Requests, nesting, values, and output are bounded. Header and claims roots must be JSON objects containing valid UTF-8 without raw control bytes.
+
+This function does not replace typed digest, HMAC, password, randomness, or constant-time comparison APIs. It exposes no raw signing, arbitrary curve/digest selection, encryption, or generic OpenSSL access. Keep returned private JWKs secret.
+
+:example
+DValue key_request;
+key_request["operation"] = "key_generate";
+key_request["algorithm"] = "ES256";
+DValue key = crypto_operation(key_request);
+
+DValue sign_request;
+sign_request["operation"] = "jwt_sign";
+sign_request["algorithm"] = "ES256";
+sign_request["private_jwk"] = key["private_jwk"];
+sign_request["protected_header"]["typ"] = "JWT";
+sign_request["claims"]["iss"] = "https://client.example";
+DValue signed_jwt = crypto_operation(sign_request);
+print(signed_jwt["ok"].to_bool() ? "signed" : "failed", "\n");