git 'fatal: bad object', 'error: object file ... is empty' or 'missing blob/tree' - how do I check and recover a corrupt repository?

Cause: one or more objects in .git/objects are missing or damaged. Common triggers: disk full or power loss during a write, a crashed sync tool or antivirus touching .git, a partially copied or cloud-synced repository, bad storage, or an interrupted gc. Fix (least destructive first): 1. Make a copy of the whole directory before you try anything (cp -a repo repo.bak). 2. Diagnose: git fsck --full. A "missing" or "broken link" report means an object is referenced but absent; "dangling" objects alone are normal after rebases and are not corruption. 3. Best recovery if a remote still has the history: clone fresh (git clone <url> repo-new). Then copy over any uncommitted working-tree files and any local-only branches you can still read. Local commits that were never pushed are the real risk, so first try to rescue them: git branch --list, git reflog, and git log <branch>. 4. Missing objects can often be re-fetched into the damaged repository: run git fetch origin. Git's docs note that fsck cannot repair missing objects itself; you must get them from a backup or another copy of the repository. 5. Empty or zero-byte object files: remove only the specific files that fsck names as bad, then fetch again. If the bad object is local only, restore it from a backup or another clone. 6. If the reflog is lost, git fsck --lost-found and git fsck --full list dangling commits you can turn back into a branch with git branch recovered <hash>. 7. Prevent repeats: keep the repo off synced folders that lock files, fix the disk, and push regularly. Verify: git fsck --full reports no missing or corrupt objects, git status works, and git log shows the history you expect. Sources: https://git-scm.com/docs/git-fsck https://git-scm.com/book/en/v2/Git-Internals-Maintenance-and-Data-Recovery