c5a6871f created the key once and never wrote it again, so a step that kept moving was bounded from its first
movement (issue 1930). Arm now creates the key when absent; one ending no earlier is armed already; one ending
earlier is written again by an update against the revision read, carrying the bound's time to live; a waiter
whose update loses reads the key again and takes the newer bound as armed. The test moves a step twice past its
first bound, with two waiters each time, and reads one write per movement, its time to live, and no delete.
Builds: design 47 G A-282, A-115, §544
Claude-Session: https://claude.ai/code/session_01NcbgfGKaxw984XyAPfLm4h
jschoubben
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