fuzz jsonrpc

[jba]

We should fuzz jsonrpc message parsing to find null pointer exceptions.

[findleyr]

@jba I'm working on the conformance tests and systematically fixing the NPEs reported by @sethvargo. I'll do this as well since it's a natural extension of the conformance tests.

[findleyr]

I'm not sure this is worthwhile. I've fuzzed jsonrpc message parsing and not found null pointer exceptions--not surprising given that they are simple wrappers around encoding/json.

I suspect what you meant is to fuzz the specific MCP messages that we send to the server. Unfortunately, that seems too complicated to admit fuzzing (without inventing a complicated framework that inevitably requires us to parameterize exactly the conditions we could just test explicitly): we need a sequence of valid MCP messages that successfully initialize the server.

I think it's more productive to carefully inspect the code and craft potential failure scenarios, as I've done in #210.