Fix ContentModified errors in info view while typing

[brandondong]

Issue:

While typing up longer proofs, I frequently see an error in the info view: Error updating: Error fetching goals: Rpc error: ContentModified: File changed. (maybe it happens to me frequently because my computer is on the older side).

It's super annoying because all the usual premise/goal info in the view is temporarily cleared to display the error and I need to wait for Lean to finish its processing before the info appears again.

Here's a video with me making contrived edits to demonstrate the issue:
https://github.com/user-attachments/assets/a077a113-7821-44bc-a307-40c0b3d37bb4

I checked the code and there should already be logic in place to not clear the info view for this particular rpc error:

Root cause:

Debugging, the original rpc error is being thrown from Widget_getWidgets

However, it's being handled by discardMethodNotFound which for this type of error, will call mapRpcError. This will convert the original rpc error with its code information into an opaque Error type. This bypasses the aforementioned RpcErrorCode.ContentModified check and we end up resolving with the error string incorrectly.

Fix:

• Update discardMethodNotFound to just rethrow the original exception when it's not the special case of RpcErrorCode.MethodNotFound which it's specifically written to handle.
• This allows the info view fetch error handling code to operate on the original rpc exception. discardMethodNotFound is not used anywhere else.

[brandondong]

Before debugging, my first guess was the bug was due to a lack of return here. It will call reject but then there's nothing stopping the code from continuing further down and calling resolve.

It turns out Promise's just return the value of the first resolve/reject that you call if you decide to call more than one, TIL. Anyways, I just added an explicit return here. Not doing so will result in purely wasted work executing the logic below only for Promise to take the first result.

[mhuisi]

Thanks! Good diagnosis :-)