fix(rpc): preserve '_' prefix for extension methods and reject empty ext#883

benbrandt merged 2 commits intoagentclientprotocol:mainagentclientprotocol/agent-client-protocol:mainfrom

anaslimem:fix-ext-method-prefix-roundtripanaslimem/agent-client-protocol:fix-ext-method-prefix-roundtripCopy head branch name to clipboard