`RPC_CALL` and `RPC_RESPONSE`

Client → server: `RPC_CALL`


{
	"type": "RPC_CALL",
	"requestId": "string",
	"fnKey": "ClassName.methodName",
	"args": []
}

args is a positional array; length must match the catalog entry’s params.length.
File parameters use JSON-safe placeholders — see File uploads.

Typed in code as RpcResponse. Important fields:

Field	Description
`type`	Always `'RPC_RESPONSE'`.
`requestId`	Echo from the call.
`fnKey`	Echo from the call.
`status`	`'ok'` or `'error'`.
`result`	JSON-safe payload on success; `null` on error.
`returnType`	Declared or inferred return type string; `'error'` when failed.
`returnShape`	Structural shape string on success; `null` on error.
`label`	Active `Return` label, synthetic error label, or timeout/serialization label.
`duration`	Human-readable timing string.
`error`	`RpcErrorDetail` or `null`.
`artifacts`	Optional array of `RpcArtifactRef` (protocol v7+).

Extensible object with required kind and optional uploadUrl, objectKey, expiresAt, plus additional keys for host-specific metadata.