The PdfHandler feature $wgPdfCreateThumbnailsInJobQueue is broken, and has probably been broken for many years. Rather than fix it, I'm proposing to remove it. Instead, the very similar core feature $wgUploadThumbnailRenderMap can be used instead.
The core feature doesn't support multi-page files, but I'm adding support for that.
Change 698367 had a related patch set uploaded (by Tim Starling; author: Tim Starling):
[mediawiki/core@master] filerepo: Make $wgUploadThumbnailRenderMap work with multipage files
Change 698368 had a related patch set uploaded (by Tim Starling; author: Tim Starling):
[mediawiki/extensions/PdfHandler@master] Remove $wgPdfCreateThumbnailsInJobQueue
Change 698368 merged by jenkins-bot:
[mediawiki/extensions/PdfHandler@master] Remove $wgPdfCreateThumbnailsInJobQueue
Change 698367 merged by jenkins-bot:
[mediawiki/core@master] filerepo: Make $wgUploadThumbnailRenderMap work with multipage files
@tstarling: Hi, all related patches in Gerrit have been merged. Can this task be resolved (via Add Action... → Change Status in the dropdown menu), or is there more to do in this task? Asking as you are set as task assignee. Thanks in advance!
Documentation should be updated to show when the global was removed, maybe explaining that it broke in some previous version, and how to migrate old settings: https://www.mediawiki.org/wiki/Extension:PdfHandler
Removed outdated docs. The core feature is presumabed to already be enabled by those interested and at a scale to warrant prerendering as PDF files are a minority of files.
The documentation does not explain that the setting broke things. Also, the change hasn't be backported in 1.35.
It is probably the reason for T50700 (which was closed while the bug was still being reproduced by seomeone and with no explanation). In the 1.35 version (still supported), the setting is still available and breaks the system upon PDF upload, so people like me that enabled the setting and have no clue why it does not work cannot easily guess it is this setting that breaks.
The documentation does not explain that the setting broke things.
I think that there are no plans to do so - we shouldn't cover all and any bugs in documentation, especially if they were not popular bugs.
Also, the change hasn't be backported in 1.35.
I'm afraid there are no plans (and no need) to backport this change to the 1.35 branch.
the setting is still available and breaks the system upon PDF upload
See above: "Rather than fix it, I'm proposing to remove it". So that's expected.