feat(conversationlist): support foldables, tablets, and wide screens

[rapterjet2004]

Apple released a foldable so now everyone is going to want one, ios or android. Better implement support for wider screens now than later. Most of the logic is actually in main_split_config.xml and handled by the window manager library

Use Jetpack WindowManager activity embedding to split ConversationsListActivity and ChatActivity side by side when the window is at least 600dp wide (unfolded foldables, tablets). A placeholder is shown in the chat pane while no conversation is selected. Narrow and folded screens keep the single-pane flow.

• Chat hides the navigate-up arrow and finishes on back when embedded
• Leaving a room no longer resets shared room/signaling state once another chat has joined a different room
• Notifications open the conversation list below the chat
• Dialogs show up on the left, new screens on the right
• Functionality preserved in ChatActivity, regresses to single activity layout where windowed dependency are not available

Assisted-by: Claude Code:claude-opus-5-5

🖼️ Screenshots

Wide screen functionality

Screen_recording_20260925_134418.webm

Open vs Closed

Screen_recording_20260925_134508.webm

Defaults to single activity when windowed not available

🏁 Checklist

• ⛑️ Tests (unit and/or integration) are included or not needed
• 🔖 Capability is checked or not needed
• 🔙 Backport requests are created or not needed: /backport to stable-xx.x
• 📅 Milestone is set
• 🌸 PR title is meaningful (if it should be in the changelog: is it meaningful to users?)

🤖 AI (if applicable)

• The content of this PR was partly or fully generated using AI

[github-actions]

📱 QA build

Download	app-qa-debug.apk
QR code	Open the QR code for this download
Commit	906377a
Version	6782
Available until	7 days after this build

The QA build installs alongside a released Nextcloud app, so you can keep
using your existing install while testing.

Downloading the file requires a GitHub account, so open this link on the
device you want to test on, or transfer the APK to it.

[Copilot]

Copilot review overview

🟡 Changes recommended

The room-token ownership check can invalidate a replacement chat session when reopening the same conversation.

Review effort: Balanced
Findings: 1 · 1

Open (2)

• Prevent stale activity cleanup from invalidating reused room sessions · New
• Move ChatPlaceholder composable and preview under conversationlist/ui · New

What changed in this PR

Adds wide-screen activity embedding for foldables and tablets.

Changes:

• Adds conversation-list/chat split rules and placeholder UI.
• Adapts chat navigation and shared room cleanup.
• Opens notification chats with the conversation list underneath.

File	Description
main_split_config.xml	Defines split and placeholder rules.
strings.xml	Adds placeholder text.
ChatPlaceholderActivity.kt	Implements placeholder UI.
ChatToolbarState.kt	Adds navigation visibility state.
ChatToolbar.kt	Conditionally displays back navigation.
ChatActivity.kt	Handles embedding and room cleanup.
NextcloudTalkApplication.kt	Registers embedding rules.
MainActivity.kt	Builds the notification activity stack.
AndroidManifest.xml	Enables embedding and declares the placeholder.
build.gradle.kts	Adds Jetpack WindowManager.

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[mahibi]

i had some issues with this PR when testing, but it might be a combination with the user handling before #6787
I can revisit the PR when it's based on the changes of 6787

on first login i saw this. It was solved when clicking on other conversations:

appbar is overlayed:

dialogs pop up on the left (thats okay for now, maybe something for followups later)

Whenever i click into the message input field the chat jumps down:

Screen_recording_20261001_151329.webm

[ToteMeiSter]

Thanks for this PR. I tested it on a Huawei foldable (DEL-LX9), unfolded. The split does not appear: the list and the chat open one after the other, as on a phone.

Diagnostics on that device:

• SplitController.splitSupportStatus = SPLIT_UNAVAILABLE
• window extensions version 1
• Build.VERSION.SDK_INT seen by the app: 31
• window 707×773 dp, so the 600 dp threshold of the split rules is met
• the rules are registered, but they are silently ignored: no error, no exception, no layout change

So on devices without Activity Embedding support from the OEM, this PR has no effect.

As an example of a fallback for such devices: https://github.com/ToteMeiSter/talk-android/tree/feat/two-pane-switch-in-place
When the window is sw600dp and the split is not available, ChatActivity shows the conversation list beside the chat (two panes inside one activity). A tap on another conversation switches the chat in place; the list and its scroll position stay. The earlier prototype is on the branch https://github.com/ToteMeiSter/talk-android/tree/test/foldable-6782 (the chat activity is recreated on each switch).

Would a fallback like this be in scope, or do you prefer to keep Activity Embedding only?

AI disclosure: the diagnostics and the fallback branch were prepared with Claude Code (claude-opus-5-5) and reviewed by the author. The author tested the fallback on the same device: two panes, switching conversations in place, rotation.