Add helper functions to distinguish between jsonRPC message types

[fredericbarthelet]

Added simple type guard functions isJSONRPCRequest, isJSONRPCResponse and isJSONRPCNotification relying on existing schemas

Motivation and Context

This is to avoid "key" in message conditions in the codebase and ensure condition are actually handling properly formatted message. This helper functions are also quite handy to avoid having to implement custom type guards in custom transport librairies - i.e. https://github.com/fredericbarthelet/middy-mcp/blob/df6e932d60aef4fad9ef436d1466057f773f1fb6/src/HttpServerTransport.ts#L4-L11

How Has This Been Tested?

There is no dedicated test file for types.ts but existing tests in protocol.test.ts are used to make sure assertion are the same.

Breaking Changes

No breaking changes

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

[jmorrell-cloudflare]

+1 for these. I've been using the Schema.safeParse for this, but helper functions would be a lot nicer and discoverable

[ihrpr]

Thank you. Looks good!

[ihrpr]

@fredericbarthelet, looks like tests are failing, please can you take a look?

[fredericbarthelet]

@fredericbarthelet, looks like tests are failing, please can you take a look?

Sorry about that, indeed missing a condition on RPC error response. Now fixed. All tests passing locally :)