I am glad that someone else shares the idea that it should be possible to set tags manually.

Here is a list of API actions which need to be able to set tags:

• action=wbcreateclaim
• action=wbcreateredirect
• action=wbeditentity
• action=wblinktitles
• action=wbmergeitems
• action=wbremoveclaims
• action=wbremovequalifiers
• action=wbremovereferences
• action=wbsetaliases
• action=wbsetclaim
• action=wbsetclaimvalue
• action=wbsetdescription
• action=wbsetlabel
• action=wbsetqualifier
• action=wbsetreference
• action=wbsetsitelink

Makes sense to me.
Do other modules outside Wikibase already allow it?

See the linked task.

There currently seem to be at least two workarounds for this missing feature:

• an AbuseFilter that matches on the edit summary and adds the tag
• a gadget that uses action=tag to tag its edit after it has been made

@darthmon_wmde I’ve already started working on this (as part of Wikidata Bridge task T227003), so I’m not sure it makes much sense to unassign me…

To clarify: for Wikidata Bridge we likely only need support in wbeditentity, but the most reasonable implementation (as far as I can tell) ends up adding support to almost all other modules as well. The exception are modules that create a redirect rather than a regular entity edit – I’ll leave those aside for now. (Also, I’m not implementing this for modules outside of Wikibase, i. e. WikibaseLexeme.)

Change 528221 had a related patch set uploaded (by Lucas Werkmeister (WMDE); owner: Lucas Werkmeister (WMDE)):
[mediawiki/extensions/WikibaseLexeme@master] Add $tags parameter to {Form,Sense}Store::saveEntity()

https://gerrit.wikimedia.org/r/528221

Change 528222 had a related patch set uploaded (by Lucas Werkmeister (WMDE); owner: Lucas Werkmeister (WMDE)):
[mediawiki/extensions/Wikibase@master] Add $tags parameter to EntityStore, EditEntity

https://gerrit.wikimedia.org/r/528222

Change 528223 had a related patch set uploaded (by Lucas Werkmeister (WMDE); owner: Lucas Werkmeister (WMDE)):
[mediawiki/extensions/Wikibase@master] Add tags parameter to editing API modules

https://gerrit.wikimedia.org/r/528223

Actually, let’s split this task up after all. Disregard the gerritbot comments, I’ll move those patches to one of the subtasks.