Extend CapData with top level iface information #2991
Description
What is the Problem Being Solved?
Some systems like the SwingSet kernel or proxy marshallers only need to translate slots. Having alleged / debugging information about what these slots represent would be beneficial for these systems. Currently such information is nested inside the body, which requires fully unserializing the CapData to extract it.
Description of the Design
An optional top level ifaces property for CapData, as an array of alleged iface corresponding to the slots.
Security Considerations
None
Scaling Considerations
If we want to maintain backwards compatibility, we will need to include iface in both the body and this new ifaces field, which could be wasteful.
Compatibility Considerations
Marshallers aware of this field would be able to use either this or the body info. They may want to place the iface info in both the body and the new field for compatibility with older marshallers.
Some patterns/shapes have been defining the structure of CapData which may make it difficult to add new fields in a compatible way.