Why refuse a job at all instead of just starting it?

Because a browser tab is not a place a nine-hour job survives, and a progress bar that will still be moving tomorrow is worse than a refusal today. The thresholds are set so a refused job is obviously refused rather than marginally so.

Is a refusal about capability or about patience?

Patience, and the page would rather say that than imply a technical limit it does not have. Nothing breaks at five minutes a file. It is a policy line, set where a queue stops being something a person will sit through, and it is stated as policy rather than dressed up as physics.

What happens to the files that are refused?

They are named, counted, and moved to the arithmetic path, which finishes each of them in well under half a second. They are not dropped and the archive is not short. The run report says which ones took that route.

Why does the envelope halve on an iPhone?

Lower canvas ceilings, and an operating system that reclaims a backgrounded tab under memory pressure. A five-hundred-file queue that would finish on a laptop is a queue that dies at file three hundred on a phone, so five hundred is not offered there at all.

What this queue will take

A refusal needs a page to point at rather than a tooltip, and this is that page. Everything here is published in advance so a set can be judged before it is dropped, not after twenty minutes of it have already run.

What this queue is for

Three bands, checked against the whole set
Band	Condition	Behaviour
Runs	ESPCN, long edge ≤ 1,500 px, up to 500 files	Starts as soon as the estimate is accepted
Warns	ESPCN to 2,400 px, or Real-ESRGAN at ≤ 600 px and ≤ 50 files	Estimate shown in red; an explicit second confirmation
Refused	Any single file estimated over 5 minutes, or a queue estimated over 4 hours	Excluded from the model path by name, with the number attached

The two refusals are different in kind. The queue-level one stops the job: four hours is where this site stops starting work it does not believe will finish, and the way past it is a smaller factor, a smaller set or the arithmetic path. The file-level one does not stop anything — those files are excluded from the model pass individually and go through Lanczos3 instead.

Running a folder

A refusal, as the tool words it

Nine of these are twelve-megapixel photographs. At the tile geometry Real-ESRGAN runs at, that is about 970 passes each, roughly 19 minutes a file on this machine — nearly three hours for those nine alone. They are excluded from the model pass and go through Lanczos instead. The other 205 run as estimated.

That sentence is generated from the same function that produces the estimate, so it cannot say one thing while the queue does another. The counts, the megapixels and the minutes are all read off your set.

On an iPhone or iPad

Every number above halves. The long-edge ceilings halve, the file counts halve, and 500 files is not offered. That envelope is inferred from the platform’s known canvas limits rather than validated on real hardware, and it will be tightened or relaxed once it has been — which is a thing this page would rather record than quietly assume.

What it opens, what it refuses

Animated GIF and animated WebP are refused per file. Flattening an animation to its first frame and calling it upscaled is not a behaviour this queue has.
A CMYK JPEG is spotted by its Adobe APP14 marker during enumeration and flagged. The browser converts it to sRGB on the way in, the colours move, and nobody should discover that in a live listing.
Files past this browser's bitmap ceiling are excluded during enumeration rather than discovered at file 300.
A file whose header says it is a picture and which then will not give up its dimensions gets its own row and its own reason — that is what a truncated download looks like. A zero-byte file, or something that was never an image, is counted on the dismissed line instead of being listed.
The four-hour and five-minute lines are policy, not physics. They are stated that way here rather than implied to be limits of the machine.

Asked mid-run

Why refuse a job at all instead of just starting it?: Because a browser tab is not a place a nine-hour job survives, and a progress bar that will still be moving tomorrow is worse than a refusal today. The thresholds are set so a refused job is obviously refused rather than marginally so.
Is a refusal about capability or about patience?: Patience, and the page would rather say that than imply a technical limit it does not have. Nothing breaks at five minutes a file. It is a policy line, set where a queue stops being something a person will sit through, and it is stated as policy rather than dressed up as physics.
What happens to the files that are refused?: They are named, counted, and moved to the arithmetic path, which finishes each of them in well under half a second. They are not dropped and the archive is not short. The run report says which ones took that route.
Why does the envelope halve on an iPhone?: Lower canvas ceilings, and an operating system that reclaims a backgrounded tab under memory pressure. A five-hundred-file queue that would finish on a laptop is a queue that dies at file three hundred on a phone, so five hundred is not offered there at all.