List of 'Collaborators' not correct

When I share a note with friends, I do not appear in the list of 'collaborators' for them.

Concrete example:
I click 'Share' to share a note with a friend.
I click 'Share' again and I can see my friend in the list of 'collaborators'.
But when my friend goes to my note and clicks 'Share', the list of 'collaborators is empty.
Thus, he has no clue who shared what with him after a while.

Start by reproducing the sharing flow described: share a note, inspect the collaborators list as the owner, then inspect it as the recipient. Trace how each view obtains its collaborator data; done means the recipient sees the people who shared the note and the list remains consistent between both views.

Written by the indexing model from the issue text.