fix: additional WebRTC call hardening

- CallActivity.onDestroy: use standalone CoroutineScope instead of
  lifecycleScope which is cancelled during super.onDestroy(), ensuring
  hangup/reject signaling events are reliably published
- disposePeerSession: remove videoSenders entry for the departing peer
  to prevent stale RtpSender references leaking after PeerConnection
  disposal
- initiateGroupCall: detect when all PeerConnection creations fail and
  hang up immediately instead of leaving the call in Offering state
  until the 60-second timeout

https://claude.ai/code/session_017HrFJNxD6zrGwiZ3s69xTh

amethyst/src/main/java/com/vitorpamplona/amethyst/service/call/CallController.kt

@@ -220,6 +220,7 @@ class CallController(
 
             callManager.beginOffering(callId, peerPubKeys, callType)
 
+            var successCount = 0
             for (peerPubKey in peerPubKeys) {
                 try {
                     val webRtcSession = withContext(Dispatchers.IO) { createWebRtcSession(peerPubKey) }
@@ -230,10 +231,16 @@ class CallController(
                             callManager.publishOfferToPeer(peerPubKey, peerPubKeys, callType, callId, sdp.description)
                         }
                     }
+                    successCount++
                 } catch (e: Exception) {
                     Log.e(TAG, "Failed to create PeerConnection for ${peerPubKey.take(8)}", e)
                 }
             }
+            if (successCount == 0) {
+                Log.e(TAG, "All PeerConnection creations failed, hanging up")
+                _errorMessage.value = "Failed to start call: could not create any connections"
+                callManager.hangup()
+            }
         }
     }
 
@@ -576,6 +583,7 @@ class CallController(
     // ---- Per-peer cleanup ----
 
     fun disposePeerSession(peerPubKey: HexKey) {
+        videoSenders.remove(peerPubKey)
         val entry = peerSessionMgr.removeSession(peerPubKey)
         if (entry != null) {
             try {

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/call/CallActivity.kt

@@ -46,7 +46,10 @@ import com.vitorpamplona.amethyst.ui.StringResSetup
 import com.vitorpamplona.amethyst.ui.screen.ManageRelayServices
 import com.vitorpamplona.amethyst.ui.screen.ManageWebOkHttp
 import com.vitorpamplona.amethyst.ui.theme.AmethystTheme
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.NonCancellable
+import kotlinx.coroutines.SupervisorJob
 import kotlinx.coroutines.launch
 import kotlinx.coroutines.withContext
 
@@ -213,13 +216,13 @@ class CallActivity : AppCompatActivity() {
 
         // Safety net: if the Activity is destroyed while a call is still
         // ringing/offering, ensure the call is hung up so audio stops.
-        // Use NonCancellable so the signaling event is published even
-        // though the lifecycle scope is being cancelled.
+        // Use a standalone CoroutineScope because lifecycleScope is cancelled
+        // during super.onDestroy() and may drop suspend work.
         val manager = CallSessionBridge.callManager
         when (manager?.state?.value) {
             is CallState.IncomingCall -> {
-                lifecycleScope.launch {
-                    withContext(NonCancellable) { manager.rejectCall() }
+                CoroutineScope(SupervisorJob() + Dispatchers.Main.immediate).launch {
+                    manager.rejectCall()
                 }
             }
 
@@ -227,8 +230,8 @@ class CallActivity : AppCompatActivity() {
             is CallState.Connecting,
             is CallState.Connected,
             -> {
-                lifecycleScope.launch {
-                    withContext(NonCancellable) { manager.hangup() }
+                CoroutineScope(SupervisorJob() + Dispatchers.Main.immediate).launch {
+                    manager.hangup()
                 }
             }