android: end call on stem press during a call

Once setupStemActions() marks the mute press as customized during a call,
the firmware stops handling the end-call press natively and forwards every
press to the app. handleCallStemPress only intercepted the mute press, so
end-call presses fell through to the user's normal stem action (play/pause,
next track, etc.) and never ended the call.

Identify the end-call press as the opposite of the mute press from
CALL_MANAGEMENT_CONFIG and route it through rejectCall(), which already
handles both telephony (TelecomManager.endCall) and VoIP (HEADSETHOOK
fallback for Teams/Zoom/Meet).

Author: nikos

android/app/src/main/java/me/kavishdevar/librepods/services/AirPodsService.kt

@@ -1280,26 +1280,33 @@ class AirPodsService : Service(), SharedPreferences.OnSharedPreferenceChangeList
 
     /**
      * Handles a stem press during an active call. Returns true if the press was
-     * the configured mute press type and was handled here; false otherwise (the
-     * caller should fall through to normal stem-action handling).
+     * either the configured mute press or the configured end-call press; false
+     * otherwise (the caller should fall through to normal stem-action handling).
      *
-     * The end-call press type is intentionally NOT handled here so the OS / AirPods
-     * native HFP behavior can end the call (which works for both telephony and VoIP).
+     * Once we mark any press as customized in setupStemActions() during a call,
+     * the firmware stops handling end-call natively and forwards every press to
+     * us, so we have to end the call ourselves.
      */
     private fun handleCallStemPress(pressType: StemPressType): Boolean {
         // CALL_MANAGEMENT_CONFIG byte[1]: 0x02 = mute on double press (flipped), 0x03 = mute on single press (default)
         val callConfig = aacpManager.getControlCommandStatus(
             AACPManager.Companion.ControlCommandIdentifiers.CALL_MANAGEMENT_CONFIG
         )?.value
         val muteIsDoublePress = callConfig?.getOrNull(1) == 0x02.toByte()
-        val isMutePress = (pressType == StemPressType.SINGLE_PRESS && !muteIsDoublePress) ||
-            (pressType == StemPressType.DOUBLE_PRESS && muteIsDoublePress)
-        Log.d(TAG, "Call stem press: $pressType, muteIsDoublePress=$muteIsDoublePress, isMutePress=$isMutePress")
-        if (isMutePress) {
-            toggleMicMute()
-            return true
-        }
-        return false
+        val mutePressType = if (muteIsDoublePress) StemPressType.DOUBLE_PRESS else StemPressType.SINGLE_PRESS
+        val endCallPressType = if (muteIsDoublePress) StemPressType.SINGLE_PRESS else StemPressType.DOUBLE_PRESS
+        Log.d(TAG, "Call stem press: $pressType, mutePressType=$mutePressType, endCallPressType=$endCallPressType")
+        return when (pressType) {
+            mutePressType -> {
+                toggleMicMute()
+                true
+            }
+            endCallPressType -> {
+                rejectCall()
+                true
+            }
+            else -> false
+        }
     }
 
     private fun toggleMicMute() {