Function cache_dir 

pub fn cache_dir() -> PathBuf

Directory holding pre-converted HEIC thumbnails, keyed by content hash rather than file path, the same photo scanned into different databases only needs converting once. Mirrors the convention hf-hub already uses for cached model weights under ~/.cache/huggingface/.

Lives under VIDERE_HOME when that is set, and under ~/.cache/videre otherwise. The override exists because this cache was previously keyed on $HOME alone, which nothing in the test suite isolates: every cargo test --workspace run therefore pruned the developer’s real thumbnail cache, since a temp test database shares no hashes with it and every cached file reads as an orphan. Two prune tests running in parallel then raced each other’s deletions and failed on the second one’s missing files, which is how this was found.

Deleting a thumbnail is not data loss, but it is expensive to undo: a HEIC full-resolution decode costs ~7.6s, against ~108ms to read a cached one.

The default path is unchanged when VIDERE_HOME is unset, so this does not move any existing user’s cache.