specify kernel-worker datatype limitations (errors, ...) precisely

[warner]

As mentioned in #2936:

In the long run, we need to nail down what exactly we're willing to tolerate in console.log calls, what precisely is the set of values that might appear in deliveries and syscalls, and make sure all our manager-worker communication pathways can support that full set. Our deliveries and syscalls are fairly conservative, and were designed to be JSON serializable, so it's really console.log that's the outlier.

Originally posted by @dckc in #2936 (comment)

[erights]

Hi @warner I'm joining you as co-assignee on this one.

[erights]

See #2936 (comment)

[dckc]

In particular, serializing errors according to best practices seems useful.
see #3000