Thank you for noticing this. This is probably a regression from T209661: The transclusion/template dialog's Apply changes action is always enabled. Cite dialog internally uses the template dialog, and I should have tested it instead of assuming it works.

ve.ui.MWCitationDialog has a bunch of weird code calling this.actions.setAbilities() (added in rEVEDda5398909e3b: Don't allow inserting blank citations), which seems to conflict with ve.ui.MWTemplateDialog's setApplicableStatus() calling the same method.

At a glance, I suspect we can remove all of that, and instead override setApplicableStatus() to not allow inserting blank citations.

Actually, nevermind. It was broken by rECITfdde5b71af7c: Update eslint-config-wikimedia to 0.9.0. But we should file a tech debt that for the other thing.

Change 476443 had a related patch set uploaded (by Bartosz Dziewoński; owner: Bartosz Dziewoński):
[mediawiki/extensions/Cite@master] ve.ui.MWCitationDialog: Fix condition for enabling insert/apply action

https://gerrit.wikimedia.org/r/476443

Change 476443 merged by jenkins-bot:
[mediawiki/extensions/Cite@master] ve.ui.MWCitationDialog: Fix condition for enabling insert/apply action

https://gerrit.wikimedia.org/r/476443

In T210686#4784077, @matmarex wrote:

ve.ui.MWCitationDialog has a bunch of weird code calling this.actions.setAbilities() (added in rEVEDda5398909e3b: Don't allow inserting blank citations), which seems to conflict with ve.ui.MWTemplateDialog's setApplicableStatus() calling the same method.

At a glance, I suspect we can remove all of that, and instead override setApplicableStatus() to not allow inserting blank citations.

In T210686#4784097, @matmarex wrote:

Actually, nevermind. It was broken by rECITfdde5b71af7c: Update eslint-config-wikimedia to 0.9.0. But we should file a tech debt that for the other thing.

Filed T210796: The citation (with template) dialog's Apply changes action is always enabled.