A read within IDENTITY_SETTLE_MS of a file's last write records no
identity, and a later read of the same bytes in the same frontend does.
FrontendInputTracker.record compared the two probes as JSON and marked
the snapshot unstable. A build or coverage run that read its entry
before and after that point then published no cache entry: the exact
repeat of a build lowered again, and a coverage verdict was not replayed.
Two file probes with the same digest now merge into one that keeps the
settled identity; any other difference still marks the snapshot
unstable.
Chris Tate
dec2b8a454