The guard form (call/cc + handler-bind expansion) doesn't survive async
IO suspension — the CEK continuation from guard's call/cc captures frames
that become invalid after the VM resumes from hs-wait. Replacing guard
with cek-try (which compiles to VM-native OP_PUSH_HANDLER/OP_POP_HANDLER)
avoids the CEK boundary crossing.
The test runner now executes: suspends on hs-wait, resumes, runs test
actions, and test assertions fire correctly. The "Not callable: nil"
error is eliminated. Remaining: test assertion errors from iframe content
not loading fast enough (timing issue, not a framework bug).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
giles
b12ec746a2