Claude Code Deleted My To-Do List Twice: AI Isn’t Perfect, and My Synology Backup Saved Me

Every morning, I have Claude Code (a tool that lets you hand tasks over to AI) tidy up the to-do list I keep in Obsidian (a note-taking app).

One morning, while it was doing the usual, Claude Code told me this:

“Sorry, I messed up.”

…

I couldn’t help laughing a little. “What did you do?!” (；´Д｀A

When I opened the file, my to-do list was completely blank (￣∇￣)

And this was the second time.

What you’ll find in this post
・The two times Claude Code wiped my to-do list, and why it happened
・How I got the file back from Synology’s “Previous Versions”
・The three layers of protection I use now, so a lost file comes back on its own
・Ways to keep earlier versions of your files, even without a Synology

“Sorry, I messed up”

Only one file was gone: my to-do list.

It didn’t wipe out all my other notes. Just that one particular file.

And because I was backing things up with Synology, I stayed fairly calm. “Well, I’ll figure something out,” I thought.

But if I hadn’t had a backup… I think I would have been in real trouble.

Just to see, I pretended I had no backup and asked Claude to put the file back. The answer was that it couldn’t, because the file is managed in Obsidian. Luckily, I’d always had at least some sense of why backups matter, so I got my data back right away.

My to-do list had about 900 lines in it: blog plans, preparations for my UK trip, even the dates when train tickets go on sale ((((；ﾟДﾟ))))))) So yes, I broke into a bit of a cold sweat.

But this wasn’t the first incident.

The first time: the whole file was rewritten, and its contents vanished (September 2026)

The first time, Claude Code was updating my to-do list and rewrote the entire file from scratch, and the contents disappeared.

After that, I made a rule: “Never rewrite an existing file from scratch.”

The second time: I had a rule, and it still happened (October 2026)

Even with that rule in place, it happened again.

The second time, I had said “good morning” to start my morning routine, and Claude Code was in the middle of adding items to my to-do list.

One step in the way it rewrote the file was in the wrong order: it emptied the file before reading what was in it. It read the empty file and saved it, still empty. That’s how the list went blank.

The rule I had made after the first time only said “don’t rewrite the whole file,” so it didn’t protect against this kind of edit.

AI isn’t perfect either.

While your rules are still being put in place, there will always be gaps, so it’s important to build things up carefully, one step at a time. And always have a way to restore your files. That’s the real key.

I got it back because Synology keeps “Previous Versions”

Both times, I got the file back the same way.

I automatically back up the files on my computer to a Synology at home (a NAS, which is your own personal data storage that sits in your house). I use an app called Synology Drive, and every time a file changes, it keeps several earlier versions of it.

So all I did was:

1. Open the “Previous Versions” of my to-do list file in Synology Drive
2. Pick the version from before it was wiped (one version back) and download it
3. Use that to put the file back

That was all it took.

The second time, the previous day’s version was still there, with every change up to the day before. All I lost was what I had added that morning…

By the way, Obsidian also has a “File recovery” feature. But the only version it had was an old one from a few days earlier. It seems that changes Claude Code makes from outside Obsidian don’t get recorded there.

Also, I don’t use Time Machine (the backup feature built into the Mac) in the first place. I no longer have an external hard drive, so I back up to my Synology instead.

I’ve written about how my Synology Drive backups work in more detail here: How I back up my Claude files with Synology Drive (in Japanese) / Moving Obsidian from Google Drive to Synology so I can use it on my iPhone too (in Japanese)

Now I have three layers of protection, so a lost file comes back on its own

Since it happened twice, I now protect my files in three layers.

1. A rule: Whenever Claude Code changes an existing file, it always uses a safe method
2. A safe way to edit: Read the whole file before writing. If the result would be empty or much smaller than before, stop without writing
3. An automatic watcher: Every time Claude Code does some work, the files get checked. If a file has gone empty, it’s restored automatically. If a file shrinks to less than half its size, the work stops and I get notified. It also keeps the last good version, plus older versions

I especially like the third one, the watcher that puts files back automatically.

Whether a person deletes something by accident or the AI does, by the time you notice, it’s already back ♪( ´▽｀)

Even without a Synology, you can keep earlier versions

I’m sure plenty of people are thinking, “I don’t have a Synology.”

But there are actually quite a few ways to keep earlier versions of your files.

(As of October 2026. Check each service’s official help pages for details.)

Which one is best depends on your computer, your apps and where you keep your important files. Pick whatever fits you, and just make sure earlier versions are being kept. I think that’s what matters most.

If, like me, you want your own data storage at home that keeps many generations of backups, I’d recommend a Synology.

Summary: the more you leave to AI, the more you need a way to get things back

• Claude Code wiped my to-do list twice
• Both times, I downloaded the previous version from Synology’s “Previous Versions” and got it back
• Now I have three layers of protection: a rule, a safe way to edit and a watcher that restores files automatically
• Even without a Synology, you can keep earlier versions with Time Machine, Google Drive, Dropbox, OneDrive and others

AI is really useful, and it helps me every single day.

But AI isn’t perfect either. Every now and then, out of nowhere, something disappears.

That’s why you should always keep backups. If you have a way to get things back, then even when you hear “Sorry, I messed up,” you can just laugh and ask, “What did you do?” (lol)

After Hearing About Claude Token Theft, I Checked My Own Auth Tokens — and Found 27 of Them

A news story about Claude account hijacking made me check my own VSCode auth tokens — and I found 27 of them sitting there. Here’s what I learned, including a bug where the revoke feature didn’t actually work for months.

あわせて読みたい

Related post: After reading an Anki forum post about an important deck disappearing, I checked all eight years of my own backups (in Japanese)

References:

• Back up your Mac with Time Machine (Apple Support)
• Check activity & file versions (Google Drive Help)
• Dropbox version history overview (Dropbox Help)
• Restore a previous version of a file stored in OneDrive (Microsoft Support)