fix: address critical audit findings

#3 JSON escaping: CallIceCandidateEvent.serializeCandidate() now
escapes backslashes and quotes in SDP/sdpMid strings before
interpolation. Prevents malformed JSON when SDP contains special
characters.

#4 Thread safety: remoteDescriptionSet changed from Boolean to
AtomicBoolean to prevent race conditions between WebRTC callback
threads and main thread accessing the flag simultaneously.

#5 Async cleanup: hangup() no longer calls cleanup() synchronously
after launching the coroutine. Cleanup is now triggered by the
CallManager state collector when Ended state is reached, avoiding
resource disposal during active WebRTC callbacks.

#7 EglBase leak: createWebRtcSession() now wraps initialize() and
createPeerConnection() in try-catch that disposes the session on
failure, preventing EGL context leaks from failed initialization.

#10 SDP failure: createOffer/createAnswer onCreateFailure() now
calls onError() to surface SDP creation failures to the user
instead of silently logging them.

#11 Notification age: EventNotificationConsumer now uses
CallOfferEvent.EXPIRATION_SECONDS (20s) instead of hardcoded 30s
to align with the actual event expiration.

https://claude.ai/code/session_017hZm7yu7CzmcQgZGSaqSXS

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

@@ -55,7 +55,9 @@ class CallController(
 ) {
     private var webRtcSession: WebRtcCallSession? = null
     private val callFactory = WebRtcCallFactory()
-    private var remoteDescriptionSet = false
+    private val remoteDescriptionSet =
+        java.util.concurrent.atomic
+            .AtomicBoolean(false)
     private val pendingIceCandidates = CopyOnWriteArrayList<IceCandidate>()
     val audioManager = CallAudioManager(context)
 
@@ -117,7 +119,7 @@ class CallController(
         scope.launch {
             val callId = UUID.randomUUID().toString()
             _errorMessage.value = null
-            remoteDescriptionSet = false
+            remoteDescriptionSet.set(false)
             pendingIceCandidates.clear()
 
             try {
@@ -154,7 +156,7 @@ class CallController(
 
         scope.launch {
             _errorMessage.value = null
-            remoteDescriptionSet = false
+            remoteDescriptionSet.set(false)
             // Don't clear pendingIceCandidates here — they were buffered while ringing
 
             try {
@@ -197,11 +199,11 @@ class CallController(
     fun onIceCandidateReceived(event: CallIceCandidateEvent) {
         try {
             val candidate = IceCandidate(event.sdpMid(), event.sdpMLineIndex(), event.candidateSdp())
-            if (webRtcSession != null && remoteDescriptionSet) {
+            if (webRtcSession != null && remoteDescriptionSet.get()) {
                 Log.d(TAG) { "Adding ICE candidate directly: ${candidate.sdp.take(50)}" }
                 webRtcSession?.addIceCandidate(candidate)
             } else {
-                Log.d(TAG) { "Buffering ICE candidate (session=${webRtcSession != null}, remoteSet=$remoteDescriptionSet)" }
+                Log.d(TAG) { "Buffering ICE candidate (session=${webRtcSession != null}, remoteSet=${remoteDescriptionSet.get()})" }
                 pendingIceCandidates.add(candidate)
             }
         } catch (e: Exception) {
@@ -210,7 +212,7 @@ class CallController(
     }
 
     private fun flushPendingIceCandidates() {
-        remoteDescriptionSet = true
+        remoteDescriptionSet.set(true)
         val session = webRtcSession ?: return
         val candidates = pendingIceCandidates.toList()
         Log.d(TAG) { "Flushing ${candidates.size} buffered ICE candidates" }
@@ -238,8 +240,10 @@ class CallController(
     fun getEglBase() = webRtcSession?.eglBase
 
     fun hangup() {
-        scope.launch { callManager.hangup() }
-        cleanup()
+        scope.launch {
+            callManager.hangup()
+            // cleanup is triggered by the state collector when Ended is reached
+        }
     }
 
     fun clearError() {
@@ -256,12 +260,12 @@ class CallController(
         _isVideoEnabled.value = true
         webRtcSession?.dispose()
         webRtcSession = null
-        remoteDescriptionSet = false
+        remoteDescriptionSet.set(false)
         pendingIceCandidates.clear()
     }
 
     private fun createWebRtcSession() {
-        webRtcSession =
+        val session =
             WebRtcCallSession(
                 context = context,
                 iceServers = IceServerConfig.buildIceServers(),
@@ -276,8 +280,14 @@ class CallController(
                 onDisconnected = { scope.launch { callManager.hangup() } },
                 onError = { error -> _errorMessage.value = error },
             )
-        webRtcSession?.initialize()
-        webRtcSession?.createPeerConnection()
+        try {
+            session.initialize()
+            session.createPeerConnection()
+            webRtcSession = session
+        } catch (e: Exception) {
+            session.dispose()
+            throw e
+        }
     }
 
     private fun onLocalIceCandidate(candidate: IceCandidate) {

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

@@ -203,6 +203,7 @@ class WebRtcCallSession(
 
                 override fun onCreateFailure(error: String?) {
                     Log.e(TAG, "Create offer failed: $error")
+                    error?.let { onError("Create offer failed: $it") }
                 }
 
                 override fun onSetSuccess() {}
@@ -231,6 +232,7 @@ class WebRtcCallSession(
 
                 override fun onCreateFailure(error: String?) {
                     Log.e(TAG, "Create answer failed: $error")
+                    error?.let { onError("Create answer failed: $it") }
                 }
 
                 override fun onSetSuccess() {}

amethyst/src/main/java/com/vitorpamplona/amethyst/service/notifications/EventNotificationConsumer.kt

@@ -631,7 +631,7 @@ class EventNotificationConsumer(
     ) {
         if (!account.isFollowing(event.pubKey)) return
 
-        if (TimeUtils.now() - event.createdAt > 30) return
+        if (TimeUtils.now() - event.createdAt > CallOfferEvent.EXPIRATION_SECONDS) return
 
         val callerUser = LocalCache.getUserIfExists(event.pubKey)
         val callerName = callerUser?.toBestDisplayName() ?: event.pubKey.take(8) + "..."

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nipACWebRtcCalls/events/CallIceCandidateEvent.kt

@@ -69,7 +69,11 @@ class CallIceCandidateEvent(
             sdp: String,
             sdpMid: String,
             sdpMLineIndex: Int,
-        ): String = """{"candidate":"$sdp","sdpMid":"$sdpMid","sdpMLineIndex":$sdpMLineIndex}"""
+        ): String {
+            val escapedSdp = sdp.replace("\\", "\\\\").replace("\"", "\\\"")
+            val escapedMid = sdpMid.replace("\\", "\\\\").replace("\"", "\\\"")
+            return """{"candidate":"$escapedSdp","sdpMid":"$escapedMid","sdpMLineIndex":$sdpMLineIndex}"""
+        }
 
         fun build(
             candidateJson: String,