I think the solution is to not use a filesystem that is broken in this way.

Note that ZFS explicitly has safeguards against total failure. No filesystem will work well with near full state when it comes to fragmentation.

This is a whataboutism. Being unable to use the filesystem, due to space full, without arcane knowledge, is not the same as "not working well".

This is a brokwn implementation.

You're misunderstanding. See the sibling thread where p_l says that this problem has been resolved, and any further occurrence would be treated as a bug. Setting the quota is only done now to reduce fragmentation (ZFS's fragmentation avoidance requires sufficient free space to be effective).

No, I'm not. They said the "recommended solution" for this issue is to use a quota.

They also said it was mainly used for other issues, such as fragmentation. In other words, this was stated as a fix for the file delete issue.

How does this invalidate my comment, that this was a broken implementation?

It doesn't matter if it will be fixed in the future, or was just fixed.

According to rincebrain, the "disk too full to delete files" was fixed "shortly after the fork" which means "shortly after 2012." My information was quite out of date.

Well I'm glad they fixed a bug, which made the filesystem unusable. Good on them, and thank you for clarification.