default_registries() is now an exported function.
Some edits for robustness:
tsv-backed registries disable
vroom altrep, (which can create file-lock issues on Windows. Even though altrep reading can provide significant speed improvements in this context with a large local registry, using LMDB for that case will still be much faster.)
Minor adjustments to some function names:
purge_cache() to easily free space used by contentid