Return spec-compliant JSON-RPC error response on panic in WithSentry middleware

[EllaSedova]

Problem

When a panic occurs inside an RPC handler wrapped by WithSentry, the defer/recover block catches the panic and reports it to Sentry, but the response returned to the client is an empty zenrpc.Response zero-value:

{
   "jsonrpc": "", 
    "id": 1
} 

This violates the https://www.jsonrpc.org/specification,

• "jsonrpc" field to always be "2.0"
• An "error" object to be present when the call fails

Fix

Two minimal changes in WithSentry:

1. Named return value - changed the anonymous return zenrpc.Response to a named return (resp zenrpc.Response) so that the deferred recovery function can assign a proper response.
2. Set error response on panic - added resp = zenrpc.NewResponseError(nil, zenrpc.InternalError, "", nil) inside the recover block, which produces a spec-compliant error response:

{
    "jsonrpc": "2.0", 
    "id": 1, 
    "error": 
    {
        "code": -32603, 
        "message": "Internal error"
    }
}

Error code -32603 (InternalError) is the appropriate code defined by the JSON-RPC 2.0 spec for internal server errors.