Strict int64 parsing via the startup validation framework: a SET but
invalid value (negative, float, null, non-numeric) aborts startup
naming the key and value. An omitted key resolves after state_dir
validation to max(75% of free bytes on the filesystem containing
<state_dir>/cache/, 500 MiB), measured via an injectable statfs probe;
the floor never applies to explicit values. Zero is valid and means
the disk cache is disabled. The effective limit is logged at startup.
sneak
8cb09b6aaf