Every single-file write now carries CultCacheStoreWriteFailed in its error
chain, above the cause. NotReplaced: creating, writing, syncing or renaming
the staging file failed, and the store file holds what it held before.
ReplacedNotDurable: the rename landed and the directory sync failed. Odin
could not tell these apart, so it kept every failed snapshot as a candidate.
The text names the path and outcome only.
fsync does not fail on a healthy filesystem, so the staging and directory
sync steps take a fault armed per thread by tests; builds outside tests never
fail there. The staging write (RLIMIT_FSIZE child) and the rename (a
directory at the store path) fail for real.
README: the write outcome, the dangling-link rule and the no-echo rule.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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