A cell that ran no longer claims it never did

Press Run on a code cell and two separate things are written. The run itself gets its own record — the activity, with its log, its status and everything the script printed. Separately, a short note is written back onto the cell: this cell was run, at this time, by this person, and here is where the log lives.

That second note is what the cell reads on your next visit. It is one small write, and very occasionally it does not land — a busy moment at startup, a refused write, content the platform cannot read back. When that happened, the note was simply absent, and the cell had nothing left to tell you with.

So it told you the only thing it could see: nothing had ever run here.

That was wrong, and it was wrong in the least helpful direction. The run had happened. Its log was still sitting in your activity list, complete. The only thing missing was the cell's pointer to it — and the cell reported that missing pointer as a missing run.

What happens now

The cell looks for its own runs instead of relying on the note. Every run writes down which cell it came from, before it starts, so the trail back exists whether or not the note was ever written.

• A cell whose note is intact behaves exactly as before — nothing extra happens, and nothing got slower.
• A cell whose note went missing now finds the run and says so, marking its output unverified: the run is real, but nothing recorded which version of the code it ran, so the cell will not claim the output matches what you are looking at.
• A cell nobody has ever run still says nothing at all. An unrun cell has no output to be wrong about, and it should not carry a warning.

"Unverified" rather than "up to date" is deliberate. The recovered run proves that the cell ran; it does not prove what it ran. Telling you the output is current when nothing substantiates that would be a wrong claim, not merely a missing one — so the cell tells you what it actually knows and lets you decide whether to run it again.