solver: include vertex Description in OpError

[sipsma]

These descriptions can be useful for callers to identify which op failed and plumb any custom metadata through to those failures.

[tonistiigi]

Iiuc OpError is intermediate error that gets converted to SolveError (that is a serializable error unlike OpError). Isn't that the one that should be updated? (There is also VertexError for good measure.)

[sipsma]

Iiuc OpError is intermediate error that gets converted to SolveError (that is a serializable error unlike OpError). Isn't that the one that should be updated? (There is also VertexError for good measure.)

Ah for Dagger's use-case we're all in-process with the solver so we use OpError directly. Can update SolveError either way too though.

VertexError seems to only support the digest atm. I guess it could be updated with the Description inside of OpError. Either would work for us, I'll go with adding to SolveError for now but can update if there's a preference.

[sipsma]

Pushed an update that puts it in SolveError too