bug(25.10): `chisel cut` failing for 25.10

[tigarmo]

Hi, we can no longer cut chisel slices for Ubuntu 25.10. Chisel version v1.4.2:

# chisel cut --release=ubuntu-25.10 --root=root base-files_bin
2026/07/21 12:46:57 Consulting release repository...
2026/07/21 12:46:58 Cached ubuntu-25.10 release is still up-to-date.
2026/07/21 12:46:58 Processing ubuntu-25.10 release...
2026/07/21 12:47:11 Selecting slices...
2026/07/21 12:47:11 Fetching ubuntu 25.10 questing suite details...
error: cannot find archive data

My unverified, naive guess for the cause is that 25.10 is EOL but it's still up in archive.ubuntu.com, and not yet in old-releases.ubuntu.com. My understanding is that this is quite common; I don't really know when the release gets moved but for example Plucky (25.04) is still up in archive. and not in old-releases..

[upils]

Your guess is right, plucky and questing are not in https://old-releases.ubuntu.com/ubuntu/dists/. So the archive does not fulfill the contract Chisel expects. However maybe this is intentional and the behavior of the archive changed, so I poked the release team and see if we need to adapt in any way.
We could temporarily work around it by setting a maintenance.end-of-life value in the future for these 2 releases in chisel-releases but that may create more problems down the line.

[upils]

I discussed it with the archive admins and we concluded that having a fallback mechanism in Chisel would be safer as this situation could last for months and it may repeat in the future when other releases are EoL. @tigarmo feel free to test the fix in the PR if you can.

[tigarmo]

Ah nice, thanks. I'm going to point rockcraft's spread tests at it and report back.

[tigarmo]

@upils I confirm that the version of Chisel on that branch fixes all broken 25.10 tests.