Does it make more sense from the perspective of finishing T180467 to skip permission checks for forms, or implement the actual permission checking for forms.
Time limit: 4 hours
Expected outcome: Answer to the question stated above, and create task(s) for implementing the outcome of the investigation,
We tracked the issue down to the class WikiPageEntityStorePermissionChecker, to a line that calls an EntityTitleLookup with a FormId. The default implementation for this is in EntityContentFactory::getTitleForId and forwards to the ContentHandler specific for the entity type, which is why early patch sets of https://gerrit.wikimedia.org/r/394072 contained an (almost empty) FormHandler.
Outcome of the investigation: It's easier to solve this properly. What needs to be done is to apply the same dispatcher pattern on the EntityTitleLookup created in WikibaseRepo::getEntityTitleLookup. All permission checks that require a Title are properly handled then (they use the Lexeme's page title then).