Migrate messages, files, and replies to seen_by architecture

[eloquence]

As part of adding SecureDrop Client support for highlighting sources with unseen submissions (freedomofpress/securedrop-client#187), we need to make server-side changes to record which journalist has seen a message, file, or reply. This breaks down into two main tasks:

• this issue: migrating the existing downloaded status and business logic to seen_by (for messages, files, and replies);

• issue Add API endpoints for seen_by #5475: adding API endpoints for updating and retrieving seen_by status

For now, this issue will have no user-facing impact on Journalist Interface users.

Definitions

"Seen" message, file, or reply:

• in the Journalist Interface: message/reply/file download was initiated via browser by a specific user, or reply was sent by a specific user
• in the SecureDrop Client: message/reply/file widget (!) was displayed in conversation view by a specific user

“Read”: terminology currently used in the Journalist Interface to indicate that a submission has been downloaded by any user

Technical specification

A working draft specification can be found here:
https://docs.google.com/document/d/1szPEKI1gTpRiM_YI87plKgiW39T7zT4Y4HG0uFnsJD4/edit#heading=h.5llqq3xyh04w

Functional requirements

The following requirements are in scope of this issue:

• "Seen by" attribution: When I download a submission or reply via the Journalist Interface, it is recorded as seen by me in the database.

• Replies are always seen: When I send a reply via the Journalist Interface, it is recorded as seen by me in the database.

• Feature equivalence: The behavior of the Journalist Interface remains the same as it is today:

  • "Unread" submissions or replies are those that have not been seen by any journalist
  • I can continue to use the "Download Unread" features of the Journalist Interface as before.
  • "Unread" submissions continue to be highlighted as such in the Journalist Interface.
  • When I migrate an existing SecureDrop installation, all data about which submissions have been downloaded is still displayed in the Journalist Interface in the same manner as before.

[prateekj117]

@eloquence If I am right, this issue will be about adding the seen_by in models and adding logic in the Journalist interface (which is accessed by browser), and the issue #5475 is for adding API endpoints for seen_by so that it can be used in SecureDrop Client.

I would like to contribute to this. I can start with adding seen_by in the models and start making its logic for the Journalist Interface.

[kushaldas]

@prateekj117 this issue/feature (and related ones) will require heavy involvement from the maintainers as we are designing totally new things based on the user research.

[prateekj117]

@kushaldas ok cool. I will look into some other issues.

[eloquence]

(Removed from the board because #5505, which is tracked on our current sprint, is expected to fully resolve this issue as specified.)