This is used when relaying: because we don't have access to the full
term, but only the projection results, we are inserting various
`(discard)`s. This is the cause of the failure in
`test/core/nesting-confusion.rkt`.
By adding `restriction-path`, we allow the inner dataspace to avoid
showing a reconstructed term to endpoints that might be able to
observe the reconstructed parts.
An alternative implementation approach is to generalize patterns in
the inner relay actor, translating all `(discard)`s into captures,
which would give us all the relevant terms that we need. The way I've
chosen to go (or at least, to try out) allows us to potentially keep
the "efficient" idea of just transmitting pattern-bound values across
some network link connecting dataspaces. The alternative would require
transmission of the full assertions, eliding no irrelevant detail.
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