fix: handle null returnType in decodeKrpcType (the actual root cause!)

The stack trace finally showed the truth: the error was in our
own decodeKrpcType, not in protobufjs. The kRPC server omits
the `return_type` field for procedures that have no return value
(e.g. AddStream, RemoveStream, all the setters). protobufjs
decodes missing message fields as null. Our cache then called
`decodeKrpcType(null)`, which did `null.code` and threw.

The null.code error message was a red herring all along — it
looked like protobufjs was looking up an enum descriptor, but it
was actually just our code accessing .code on a null parameter.

The protobufjs fixes (uint32 instead of nested-enum, adding the
game_scenes field) were real and needed — but they weren't the
cause of THIS particular failure mode.

Fix:
- decodeKrpcType accepts null/undefined and returns a NONE type
  (code 0) in that case
- Added a regression test in services.test.ts that builds a fake
  ServiceCache with a procedure whose returnType is null

packages/krpc-client/src/types.ts

@@ -78,7 +78,23 @@ export interface RawKrpcTypeMessage {
   types: RawKrpcTypeMessage[];
 }
 
-export function decodeKrpcType(raw: RawKrpcTypeMessage): KrpcType {
+/**
+ * Decode a kRPC Type protobuf message into our plain KrpcType shape.
+ *
+ * Returns a NONE-type KrpcType if `raw` is null/undefined or doesn't
+ * have a `code` field — which happens for procedures with no return
+ * value (the kRPC server omits the `return_type` field). We treat that
+ * as the NONE type code (0) rather than throwing.
+ */
+export function decodeKrpcType(raw: RawKrpcTypeMessage | null | undefined): KrpcType {
+  if (!raw || typeof raw.code !== 'number') {
+    return {
+      code: 0 as TypeCodeValue, // NONE
+      service: '',
+      name: '',
+      types: [],
+    };
+  }
   return {
     code: raw.code as TypeCodeValue,
     service: raw.service ?? '',