[imorland]

Changes proposed in this pull request:
Messages currently accepts individual recipients only. Add configurable Flarum Group recipients with admin-only initiation by default, live membership access to the full history, and persistent leaving. Include matching Realtime delivery and typing changes, preserving existing conversations on upgrades from 2.0 and current 2.x. Notification and typing regressions were reproduced with failing tests before their fixes.

Reviewers should focus on:

• Membership changes, persistent leave, and hidden Groups.
• Upgrades from 2.0 and current 2.x.
• Realtime delivery and typing after access changes.

Screenshot
Recipient picker — before

Recipient picker — after

Messages settings — before

Messages settings — after

Group selection recording

Necessity

• Has the problem that is being solved here been clearly explained?
• If applicable, have various options for solving this problem been considered?
• For core PRs, does this need to be in core, or could it be in an extension?
• Are we willing to maintain this for years / potentially forever?

Confirmed

• Frontend changes: tested on a local Flarum installation.
• Frontend changes: tests are green (run yarn test in js/).
• Frontend changes: tests have been added, or are not appropriate here.
• Backend changes: tests are green (run composer test).
• Backend changes: tests have been added, or are not appropriate here.
• Where applicable, changes are suitable for all supported database drivers (MySQL, MariaDB, PostgreSQL, SQLite).
• Core developer confirmed locally this works as intended.
• The description above is written by me and describes what this pull request actually does.

Required changes:

• Related documentation PR: pending (Messages and Realtime).