With cache_max_bytes omitted the cache must work out the default
limit, with an explicit 0 the disk cache must be off, and an explicit
positive value must reach the cache unchanged. newCacheConfig does not
exist yet, so this commit does not compile; the next one adds it.
Model: opus-5-5
The default limit was 75% of the space free at startup. The cache's
own files are not free space, so a fuller cache got a smaller limit
after a restart and eviction then deleted most of it. The default is
now 75% of the sum of the free space and what the cache already holds
by its own size accounting, at least 500 MiB. The cache works it out
when it opens, after the database is open, so the computation and its
tests moved from internal/config to internal/imgcache; the config only
records whether cache_max_bytes was set, and the handlers turn the
disk cache off only for an explicit 0.
Model: opus-5-5
clawbot