Function isJsonRpcMethodNotFoundError

Whether error is what networkService's request plumbing (doRequest in network.service.ts) throws for a JSON-RPC "method not found" response — i.e. no handler for the requested method has registered anywhere on the network.

Callers that want to treat "nobody is listening" as a benign outcome must key off the JSON-RPC error code, never off the human-readable text that follows it. The two producers of a method-not-found response word that text differently ('<method>' not found in rpc-server.ts, No handler found for <method> in rpc-websocket-listener.ts), and matching the text alone also matches an unrelated failure from a handler that did run and threw a message with the same words in it — turning "no validator, allow it" into "the validator rejected this, allow it anyway". The code is the only part that distinguishes the two.

The code has to be read back out of the message because doRequest flattens every RPC-level error — method-not-found and a handler throwing alike — into a thrown value whose message is JSON-RPC Request error (${code}): ${message}, with no other machine-readable marker (the richer platformErrorCode field is populated only for C# PlatformErrorCodes.WithCode throws, which a "no handler yet" response never carries — it has no error.data at all). Deriving the format from getJsonRpcRequestErrorMessagePrefix, the same producer doRequest builds the message with, keeps this matcher in lockstep with any reformat there.