inventory() read every RomFS file into memory and decompressed it before deciding whether the file can hold a
shader. On 1.1.1 that is 304,469 entries and 15.86 GiB, and the shaders live in six directories: 1,996 entries,
147 MiB, 0.9% of the bytes. The walk visits those directories and reads everything else only when the shader list
names keys it did not find there.
Measured on one install: 66.50 s -> 3.35 s for the same 27,576 shaders, key for key.
pack_shader_cache.py also rewrote its pack after every prepare although there was nothing to fold in: 2.6 s of
copying 1.37 GiB over the same entries, and a file system that then releases the old pack's blocks. It returns at
once when the cache holds no loose files.
shenjack