fix(call): restore call audio mode after audio focus interruptions

[tareko]

fix(call): restore call audio mode after audio focus interruptions

Fixes #6541

Description

The audio focus change listener in WebRtcAudioManager only logged changes (the "possibly extend support of handling audio-focus changes" TODO from the WebRTC sample was never implemented). A transient focus holder such as the telephony stack switches the global audio mode to MODE_IN_CALL and restores its own saved mode (typically MODE_NORMAL) on release, clobbering Talk's MODE_IN_COMMUNICATION. Since nothing re-asserted it, a Talk call interrupted by an incoming GSM call continued without hardware echo cancellation and proper VoIP routing — remote parties heard echo, very quiet audio, or nothing until the call was left and rejoined.

Changes:

• New AudioFocusState tracks transient focus losses; when focus returns, MODE_IN_COMMUNICATION and the selected audio route are re-asserted (guarded by the RUNNING state so late callbacks after stop() are ignored)
• Focus is now requested with AUDIOFOCUS_GAIN via AudioFocusRequest (voice-communication attributes, delayed gain accepted, no ducking) instead of the deprecated AUDIOFOCUS_GAIN_TRANSIENT hint meant for short-lived use
• stop() abandons focus via abandonAudioFocusRequest

Steps to reproduce / How to test

1. Join a Talk call (audio works both ways)
2. Receive and answer a regular phone call
3. Hang up the phone call and return to Talk
4. Speak and ask the remote party what they hear

Without this PR: echo / very quiet audio / silence until the call is restarted.
With this PR: normal two-way audio resumes when the phone call ends.

Also test: music app playing before/after the call, headset unplug (ACTION_AUDIO_BECOMING_NOISY path), joining a call while a phone call is active (delayed focus gain).

• ⛑️ Tests are included (WebRtcAudioManagerFocusTest: focus request config + restore state machine)
• 🔖 Capability is checked or not needed
• 🔙 Backport requests or not needed
• 📅 Milestone is set
• 🌸 PR title is meaningful

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Note: This PR was developed with AI assistance (opencode / Kimi K3); see the Assisted-by commit trailer.

[github-actions]

APK file: https://github.com/nextcloud/talk-android/actions/runs/32604199571/artifacts/9483779211
To test this change/fix you can simply download above APK file and install and test it in parallel to your existing Nextcloud app.
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[Copilot]

Pull request overview

This PR fixes an audio-routing regression during Talk calls after audio focus interruptions (e.g., answering/hanging up a GSM call) by re-asserting AudioManager.MODE_IN_COMMUNICATION and the selected audio route when focus is regained, ensuring proper VoIP routing and hardware AEC behavior.

Changes:

• Implement audio focus change handling in WebRtcAudioManager to restore call audio mode/route after transient focus loss.
• Switch audio focus acquisition to AudioFocusRequest with AUDIOFOCUS_GAIN and voice-communication AudioAttributes, and abandon focus via abandonAudioFocusRequest.
• Add Robolectric unit tests covering the focus request configuration and the transient-loss restore state machine.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
app/src/main/java/com/nextcloud/talk/webrtc/WebRtcAudioManager.java	Adds focus request/state tracking and re-applies MODE_IN_COMMUNICATION + routing on focus regain.
app/src/test/java/com/nextcloud/talk/webrtc/WebRtcAudioManagerFocusTest.kt	Adds unit tests for the focus request config and restore-on-gain behavior after transient loss.

Suppressed comments (1)

app/src/main/java/com/nextcloud/talk/webrtc/WebRtcAudioManager.java:173

• requestAudioFocus() can return AUDIOFOCUS_REQUEST_DELAYED when acceptsDelayedFocusGain is enabled. The current code treats any non-GRANTED result as an error, which will log a false failure in the delayed-focus scenario described in the PR and issue.

        if (result == AudioManager.AUDIOFOCUS_REQUEST_GRANTED) {
            Log.d(TAG, "Audio focus request granted for VOICE_CALL streams");
        } else {
            Log.e(TAG, "Audio focus request failed");
        }

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[mahibi]

/backport to stable-25.0.x