>> C. Set all variables in the C environment to match process-environment
>>    every time we call into the dynamic module
>>    (but this is slow and hurts performance)

I'm going to preface a solution to excessive redundant passing by pointing
out that the provenance of a piece of data is a requisite but something we
don't have.

Encoding input provenance in vector clocks is a solution to avoiding
unnecessary passing and maintaining caller and callee input synchronization
even when the callee is performing asynchronous work.

While we can use watch-variable for updates from Elisp, such as those done
by a package like envrc that creates buffer local environments, updates
from C don't have this convenience.

Protecting inputs from arbitrary mutations is a requirement to implement
this technique conveniently.  More likely, there need to be interfaces that
permit a logical clock and the value it versions to remain consistent.
Since the data needs to be immutable or else requires locking, coordination
with the GC is required.