fix(jsonrpc): avoid corrupting the offset maximum reported by 'rpc.discover'

- Changed Service.discoverSpec from any to json.RawMessage.
- Retained json.Unmarshal, validating and copying the embedded JSON without converting numbers to float64.
- Added a regression test asserting rpc.discover returns the exact literal 9223372036854775807.

Author: renatomaia

internal/jsonrpc/batchcalls_test.go

@@ -166,6 +166,18 @@ func TestJSONRPCMalformedObjectReturnsJSONContentType(t *testing.T) {
 	requireRPCError(t, decodeRPCResponse(t, rr.Body.Bytes()), nil, JSONRPC_PARSE_ERROR)
 }
 
+func TestJSONRPCDiscoverPreservesLargeIntegerLiterals(t *testing.T) {
+	s := newBatchTestService()
+	data, err := discoverSpec.ReadFile("jsonrpc-discover.json")
+	require.NoError(t, err)
+	require.NoError(t, json.Unmarshal(data, &s.discoverSpec))
+
+	rr := serveRPC(t, s, []byte(`{"jsonrpc":"2.0","method":"rpc.discover","id":1}`))
+
+	require.Equal(t, http.StatusOK, rr.Code)
+	require.Contains(t, rr.Body.String(), `"maximum":9223372036854775807`)
+}
+
 func TestJSONRPCBatchMalformedElementDoesNotPoisonValidSiblings(t *testing.T) {
 	s := newBatchTestService()
 	body := []byte(`[

internal/jsonrpc/service.go

@@ -42,7 +42,7 @@ type Service struct {
 	// overridden in tests so Serve() can be exercised without real sockets.
 	listen func(network, address string) (net.Listener, error)
 	// OpenAPI description for JSON-RPC API loaded from 'jsonrpc-discover.json' file
-	discoverSpec any
+	discoverSpec json.RawMessage
 	handlers     dispatchTable
 	// dispatchTimeout expires requests early enough to serialize a complete
 	// timeout response before the HTTP server's write deadline.