The done-frame fallback read _os_write/_memoryview/_FALLBACK_DONE_FRAME as module
globals at call time, so a single-line rebind of any of them reopened the
rebind hole the fallback exists to close. Bind them into _run locals before the
program runs, and use a bare except (which catches everything without naming
BaseException, so a rebind of that name cannot defeat the handler). The
transitive-name rebind test now also rebinds _os_write/_memoryview/
_FALLBACK_DONE_FRAME to pin the fallback's immunity.
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