Annotate exceptions arriving over JSRPC as "remote"

[jclee]

...so that they get the expected ".remote" property when tunneled to JS, like exceptions from Durable Object fetch() calls do.

[jasnell]

Any possibility of having tests with this?

[jclee]

Any possibility of having tests with this?

• I've got some on the internal PR... Will try adding workerd-specific coverage.

[jasnell]

Lgtm assuming internal ci is good

[kentonv]

A couple inconsistencies with the way "remote" is handled for fetch():

1. Here you've placed the logic on the client side to add the remote annotation, but for fetch() it happens server-side (in WorkerEntrypoint). Maybe we should keep these the same? I think this means putting the logic in JsRpcTargetBase::call() instead.
2. WorkerEntrypoint only adds the annotation to JSG exceptions, not to internal errors, but your code here doesn't seem to distinguish.

[jclee]

A couple inconsistencies with the way "remote" is handled for fetch():

1. Here you've placed the logic on the client side to add the remote annotation, but for fetch() it happens server-side (in WorkerEntrypoint). Maybe we should keep these the same? I think this means putting the logic in JsRpcTargetBase::call() instead.
2. WorkerEntrypoint only adds the annotation to JSG exceptions, not to internal errors, but your code here doesn't seem to distinguish.

• Ah, makes sense... taking a look.

[jclee]

I moved the .remote annotation from the client side of the RPC boundary to the server side, and added a check to ensure only tunneled (jsg.-prefixed) exceptions get the annotation. (I wasn't sure how to test non-remote exceptions from within the wd-test framework, but I managed to add some coverage for it on the internal PR.)