scheme-standard-env binds:
- call/cc — primary
- call-with-current-continuation — alias
Implementation wraps SX's host call/cc, presenting the captured
continuation k as a Scheme procedure that accepts a single value
(or a list of values for multi-arg invocation). Single-shot
escape semantics: when k is invoked, control jumps out of the
surrounding call/cc form. Multi-shot re-entry isn't safely
testable without delimited-continuation infrastructure (the
captured continuation re-enters indefinitely if invoked after
the call/cc returns) — deferred to a follow-up commit if needed.
Tests cover:
- No-escape return value
- Escape past arithmetic frames
- Detect/early-exit idiom over for-each
- Procedure? on the captured k
220 total Scheme tests now (62 + 23 + 49 + 78 + 8).
