src: enhance feature access `CHECK`s during bootstrap
This adds CHECK
s verifying that bootstraping has finished
before environment variables are accessed or handles/requests
are created. The latter complements a pair of existent checks,
but fails earlier and thus gives information about the call
site, effectively addressing the TODO comment there.
Checklist
-
make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
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