[longunmin]

Summary

Open the app back on the last room you were reading.

Commet currently always lands on the room list when cold-started. Most users who
open a chat app do it to continue a conversation they were in a moment ago —
especially on mobile where a phone-call, a doze, or a background-kill has closed
the app. This PR persists the last room you opened in each account and reopens
it on the next launch, mirroring the existing deep-link restore path.

This follows up on #778, which was scoped to spaces. The behavior here
covers the general (non-space) room-list case.

How it works

main_page.dart already handles "restore a room on launch" when the app is
opened via a deep link (see the block starting at
if (client == null && widget.initialRoom != null)). This PR reuses the same
pattern for the no-deep-link case and adds the persistence it needs:

• preferences.dart

  • New _rememberedRooms preference — a Map<clientIdentifier, roomIdentifier>
    stored as JSON via SharedPreferences, matching the existing
    storeRoomsListCache pattern.
  • getRememberedRoom(clientId) / setRememberedRoom(clientId, roomId).
    An empty roomId removes the entry (logout-friendly hook, even though we
    don't wire the logout cleanup in this PR — the restore path already guards
    against a stale id, so a left-behind entry simply won't restore anything).

• main_page.dart

  • In selectRoom(...): record room.client.identifier → room.identifier so
    the most recently opened room wins on next launch.
  • After the existing deep-link restore block in initState: if the user
    didn't come in via a deep link, and no room is currently selected, fetch
    the remembered room id for this client and selectRoom(...) it. We guard
    on client.isLoggedIn() and on currentRoom == null to keep the deep-link
    path and any manual navigation from being clobbered.

Multi-account: keys are per client.identifier, so logged-in accounts each get
their own remembered room. The app's existing single-"active" account model
means only one is visible on the front screen at a time, so no disambiguation
UI is needed.

What's not in this PR

• Spaces restore ([Feature] Return to last visited room when switching spaces #778): deliberately out of scope so this can be merged as a
  small, isolated change. Trivial follow-up if maintainers want it.
• Deep-link support (commetchat://room/<id>): also not included — that
  requires the URL-scheme + alias-resolution work that [Feature] Implement MSC4550 explicit links #1070 (MSC4550) is
  targeting, and I didn't want to bundle that in here.
• Widget/notification deep links into a room: same reason.

Testing

Not compiled/flutter analyzed (no Flutter toolchain on the box that produced
this). The code is small, mirrors existing patterns in preferences.dart and
the initialRoom restore block in main_page.dart, and should pass CI as-is.
Manual test plan once CI is green:

1. Log in to tcmatrix.duckdns.org → open Room A → force-stop the app → relaunch →
   expect to land in Room A.
2. Switch to Room B in a different Space → force-stop → relaunch → expect to land
   in Room B (most-recently-opened wins).
3. Open the app via the existing deep-link path (or a URL into a room) →
   expect to land in the deep-link room, not the remembered one.
4. Log out, log back in → no crash, no phantom room restore.
5. Multi-account: log in with account A (Room A), log in with account B (Room B),
   log out of A → relaunch → should land in B's last room (A is gone).

Files changed

• commet/lib/config/preferences.dart (+30)
• commet/lib/ui/pages/main/main_page.dart (+16)

Caveats / known limitations

• "Last room" is per-account-global, not per-space. If you were in Room A of
  Space X, closed the app, and last touched an in-app Space Y screen, you'll
  still come back to A. That's the right default — but flagging it so we can
  follow up on [Feature] Return to last visited room when switching spaces #778 separately.
• Doesn't persist "last room per view mode" (e.g. if you last saw the pinned /
  unread filter view, we ignore that). Trivial follow-up if wanted.

/cc @commetchat maintain — happy to adjust to fit house style / split into
smaller commits / add a unit test for getRememberedRoom/setRememberedRoom
whichever is preferred.

[Airyzz]

closing as this seems AI generated. Please stick to the contribution guide