A torn producer write (e.g. disk-full mid-copy) could leave a 0-byte P.wwi or
P.o in out/.pkgcache under a self-consistent key; cache_lookup checked only
existence, so every later build HIT and served the empty artifact forever
(silent serve-wrong). Reject size==0 on both sides, symmetric across stages:
store refuses to commit a 0-byte temp before the key write, lookup treats a
0-byte cached artifact as a MISS so existing poison self-heals on re-derive.
A valid .wwi/.o is never 0 bytes, so the guard cannot misfire.
Regression: test/wcc/989_pkgcache_poison_run.c, table-driven over
{poison P.wwi | P.o | both}, non-vacuity proven by guard-neuter.
147 KiB
147 KiB