These are machine-local files that should never be version controlled:
- .laputa-cache.json: contains absolute paths, changes on every machine
- .laputa/settings.json: per-machine UI settings
Fix: ensure_cache_excluded() now:
1. Adds both files to .git/info/exclude (git-level ignore, no .gitignore needed)
2. Runs `git rm --cached --ignore-unmatch` on vault open to un-track them
if they were committed in older vaults
This is idempotent and self-healing — existing vaults fix themselves
automatically on next app launch without any manual steps.
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