Gossip mesh topology + source-based routing (#445)

* wip mesh graph

* gossip fix

* gossip works

* source-based routing wip

* log

* update spec to be explicit about intermediate hops only

* drop duplicate hops

* add to spec

* test

* forgot comma

* source routing v2

* add compression bomb protection

* v2 source routing

* fragmented packets inherit route

* update spec

* Gossip routing tmp with connection limit fixed (#569)

* fix: r8 exception for LocationManager (#566)

* fragmented packets inherit route

* update spec

* fix connection limits

* fix: deserialization issue with routed packets

* log

* dynamic fragment size

* fragment size

* add tests

* feat(gossip): implement two-way handshake for source routing edges

- Update MeshGraphService to track directed announcements
- Require bidirectional announcements for a 'confirmed' edge
- Update RoutePlanner to strictly use confirmed edges
- Update Mesh Topology debug view to show confirmed vs unconfirmed edges (solid vs dotted)

* docs: update SOURCE_ROUTING.md with two-way handshake requirement

* evict stale peers from mesh graph service

* better logging

* fix announce spe

* fix: empty route

* fix spec

* fix: compile error in DebugSettingsSheet and potential NPE in RoutePlanner

* revert

* try again

app/src/main/java/com/bitchat/android/mesh/BluetoothConnectionManager.kt

@@ -109,11 +109,19 @@ class BluetoothConnectionManager(
             }
             // Connection caps: enforce on change
             connectionScope.launch {
-                dbg.maxConnectionsOverall.collect {
+                dbg.maxConnectionsOverall.collect { maxOverall ->
                     if (!isActive) return@collect
+                    // 1. Enforce client limits (handled by tracker)
                     connectionTracker.enforceConnectionLimits()
-                    // Also enforce server side best-effort
+                    
-                    serverManager.enforceServerLimit(dbg.maxServerConnections.value)
+                    // 2. Enforce overall limit on server connections if needed
+                    // (Tracker knows about all connections but can't disconnect servers directly)
+                    val maxServer = dbg.maxServerConnections.value
+                    val excessServers = connectionTracker.getExcessServerConnections(maxServer, maxOverall)
+                    excessServers.forEach { device ->
+                        Log.d(TAG, "Disconnecting server ${device.address} due to overall cap")
+                        serverManager.disconnectDevice(device)
+                    }
                 }
             }
             connectionScope.launch {
@@ -123,9 +131,18 @@ class BluetoothConnectionManager(
                 }
             }
             connectionScope.launch {
-                dbg.maxServerConnections.collect {
+                dbg.maxServerConnections.collect { maxServer ->
                     if (!isActive) return@collect
-                    serverManager.enforceServerLimit(dbg.maxServerConnections.value)
+                    // Enforce server specific limit
+                    serverManager.enforceServerLimit(maxServer)
+                    
+                    // Also check if this change puts us over the overall limit
+                    val maxOverall = dbg.maxConnectionsOverall.value
+                    val excessServers = connectionTracker.getExcessServerConnections(maxServer, maxOverall)
+                    excessServers.forEach { device ->
+                        Log.d(TAG, "Disconnecting server ${device.address} due to overall cap")
+                        serverManager.disconnectDevice(device)
+                    }
                 }
             }
         } catch (_: Exception) { }
@@ -261,6 +278,16 @@ class BluetoothConnectionManager(
         )
     }
 
+    fun sendToPeer(peerID: String, routed: RoutedPacket): Boolean {
+        if (!isActive) return false
+        return packetBroadcaster.sendToPeer(
+            peerID,
+            routed,
+            serverManager.getGattServer(),
+            serverManager.getCharacteristic()
+        )
+    }
+
     fun cancelTransfer(transferId: String): Boolean {
         return packetBroadcaster.cancelTransfer(transferId)
     }

app/src/main/java/com/bitchat/android/mesh/BluetoothConnectionTracker.kt

@@ -229,11 +229,17 @@ class BluetoothConnectionTracker(
      */
     fun getConnectedDeviceCount(): Int = connectedDevices.size
     
+    /**
+     * Check if connection limit is reached
+     */
     /**
      * Check if connection limit is reached
      */
     fun isConnectionLimitReached(): Boolean {
-        return connectedDevices.size >= powerManager.getMaxConnections()
+        // Respect debug override if set
+        val dbg = try { com.bitchat.android.ui.debug.DebugSettingsManager.getInstance() } catch (_: Exception) { null }
+        val maxConnections = dbg?.maxConnectionsOverall?.value ?: powerManager.getMaxConnections()
+        return connectedDevices.size >= maxConnections
     }
     
     /**
@@ -244,10 +250,9 @@ class BluetoothConnectionTracker(
         val dbg = try { com.bitchat.android.ui.debug.DebugSettingsManager.getInstance() } catch (_: Exception) { null }
         val maxOverall = dbg?.maxConnectionsOverall?.value ?: powerManager.getMaxConnections()
         val maxClient = dbg?.maxClientConnections?.value ?: maxOverall
-        val maxServer = dbg?.maxServerConnections?.value ?: maxOverall
+        // Note: maxServer is handled by GattServerManager, but we need to respect overall limit here too
 
         val clients = connectedDevices.values.filter { it.isClient }
-        val servers = connectedDevices.values.filter { !it.isClient }
 
         // Enforce client cap first (we can actively disconnect)
         if (clients.size > maxClient) {
@@ -259,23 +264,57 @@ class BluetoothConnectionTracker(
             }
         }
 
-        // Note: server cap enforced in GattServerManager (we don't have server handle here)
+        // Re-check overall cap after client cleanup
-
-        // Enforce overall cap by disconnecting oldest client connections
         if (connectedDevices.size > maxOverall) {
             Log.i(TAG, "Enforcing overall cap: ${connectedDevices.size} > $maxOverall")
             val excess = connectedDevices.size - maxOverall
-            val toDisconnect = connectedDevices.values
+            
-                .filter { it.isClient } // only clients from here
+            // Prefer disconnecting clients first to satisfy overall cap
+            val clientsToDisconnect = connectedDevices.values
+                .filter { it.isClient }
                 .sortedBy { it.connectedAt }
                 .take(excess)
-            toDisconnect.forEach { dc ->
+                
+            clientsToDisconnect.forEach { dc ->
                 Log.d(TAG, "Disconnecting client ${dc.device.address} due to overall cap")
                 dc.gatt?.disconnect()
             }
         }
     }
 
+    /**
+     * Get excess server connections that should be disconnected to satisfy limits.
+     * This allows the Manager to coordinate server disconnects since Tracker doesn't control the server.
+     */
+    fun getExcessServerConnections(maxServer: Int, maxOverall: Int): List<BluetoothDevice> {
+        val servers = connectedDevices.values.filter { !it.isClient }
+        val excessList = mutableListOf<BluetoothDevice>()
+
+        // 1. Check server specific limit
+        if (servers.size > maxServer) {
+            val excessCount = servers.size - maxServer
+            val toRemove = servers.sortedBy { it.connectedAt }.take(excessCount)
+            excessList.addAll(toRemove.map { it.device })
+        }
+
+        // 2. Check overall limit (considering we might have already removed some above)
+        // We need to count how many connections we will have after the above removals
+        val currentTotal = connectedDevices.size
+        val plannedRemovals = excessList.size
+        val projectedTotal = currentTotal - plannedRemovals
+        
+        if (projectedTotal > maxOverall) {
+            val furtherExcess = projectedTotal - maxOverall
+            // We can only remove servers here. Clients are handled in enforceConnectionLimits.
+            // Filter out devices we already planned to remove
+            val remainingServers = servers.filter { s -> excessList.none { it.address == s.device.address } }
+            val toRemove = remainingServers.sortedBy { it.connectedAt }.take(furtherExcess)
+            excessList.addAll(toRemove.map { it.device })
+        }
+
+        return excessList
+    }
+    
     /**
      * Clean up a specific device connection
      */

app/src/main/java/com/bitchat/android/mesh/BluetoothGattServerManager.kt

@@ -49,16 +49,29 @@ class BluetoothGattServerManager(
     fun enforceServerLimit(maxServer: Int) {
         if (maxServer <= 0) return
         try {
-            val subs = connectionTracker.getSubscribedDevices()
+            // Use connection tracker to get actual connected server devices
-            if (subs.size > maxServer) {
+            val servers = connectionTracker.getConnectedDevices().values.filter { !it.isClient }
-                val excess = subs.size - maxServer
+            if (servers.size > maxServer) {
-                subs.take(excess).forEach { d ->
+                val excess = servers.size - maxServer
-                    try { gattServer?.cancelConnection(d) } catch (_: Exception) { }
+                // Disconnect oldest
+                servers.sortedBy { it.connectedAt }.take(excess).forEach { d ->
+                    try { gattServer?.cancelConnection(d.device) } catch (_: Exception) { }
                 }
             }
         } catch (_: Exception) { }
     }
 
+    /**
+     * Disconnect a specific device (used by ConnectionManager to enforce overall limits)
+     */
+    fun disconnectDevice(device: BluetoothDevice) {
+        try {
+            gattServer?.cancelConnection(device)
+        } catch (e: Exception) {
+            Log.w(TAG, "Error disconnecting device ${device.address}: ${e.message}")
+        }
+    }
+    
     /**
      * Start GATT server
      */
@@ -122,9 +135,10 @@ class BluetoothGattServerManager(
             
             // Try to cancel any active connections explicitly before closing
             try {
-                val devices = connectionTracker.getSubscribedDevices()
+                // Disconnect ALL server connections
-                devices.forEach { d ->
+                val servers = connectionTracker.getConnectedDevices().values.filter { !it.isClient }
-                    try { gattServer?.cancelConnection(d) } catch (_: Exception) { }
+                servers.forEach { d ->
+                    try { gattServer?.cancelConnection(d.device) } catch (_: Exception) { }
                 }
             } catch (_: Exception) { }
             

app/src/main/java/com/bitchat/android/mesh/BluetoothMeshService.kt

@@ -172,6 +172,9 @@ class BluetoothMeshService(private val context: Context) {
             }
             override fun onPeerRemoved(peerID: String) {
                 try { gossipSyncManager.removeAnnouncementForPeer(peerID) } catch (_: Exception) { }
+                // Remove from mesh graph topology to prevent routing through stale peers
+                try { com.bitchat.android.services.meshgraph.MeshGraphService.getInstance().removePeer(peerID) } catch (_: Exception) { }
+
                 // Also drop any Noise session state for this peer when they go offline
                 try {
                     encryptionService.removePeer(peerID)
@@ -526,6 +529,10 @@ class BluetoothMeshService(private val context: Context) {
                 connectionManager.broadcastPacket(routed)
             }
 
+            override fun sendToPeer(peerID: String, routed: RoutedPacket): Boolean {
+                return connectionManager.sendToPeer(peerID, routed)
+            }
+            
             override fun handleRequestSync(routed: RoutedPacket) {
                 // Decode request and respond with missing packets
                 val fromPeer = routed.peerID ?: return
@@ -540,11 +547,15 @@ class BluetoothMeshService(private val context: Context) {
             // Log incoming for debug graphs (do not double-count anywhere else)
             try {
                 val nick = getPeerNicknames()[peerID]
+                val route = packet.route
+                val routeInfo = if (!route.isNullOrEmpty()) "routed: ${route.size} hops" else null
                 com.bitchat.android.ui.debug.DebugSettingsManager.getInstance().logIncoming(
                     packetType = packet.type.toString(),
                     fromPeerID = peerID,
                     fromNickname = nick,
-                        fromDeviceAddress = device?.address
+                    fromDeviceAddress = device?.address,
+                    packetVersion = packet.version,
+                    routeInfo = routeInfo
                 )
             } catch (_: Exception) { }
             packetProcessor.processPacket(RoutedPacket(packet, peerID, device?.address))
@@ -1020,12 +1031,26 @@ class BluetoothMeshService(private val context: Context) {
             
             // Create iOS-compatible IdentityAnnouncement with TLV encoding
             val announcement = IdentityAnnouncement(nickname, staticKey, signingKey)
-            val tlvPayload = announcement.encode()
+            var tlvPayload = announcement.encode()
             if (tlvPayload == null) {
                 Log.e(TAG, "Failed to encode announcement as TLV")
                 return@launch
             }
 
+            // Append gossip TLV containing up to 10 direct neighbors (compact IDs)
+            try {
+                val directPeers = getDirectPeerIDsForGossip()
+                if (directPeers.isNotEmpty()) {
+                    val gossip = com.bitchat.android.services.meshgraph.GossipTLV.encodeNeighbors(directPeers)
+                    tlvPayload = tlvPayload + gossip
+                }
+                // Always update our own node in the mesh graph with the neighbor list we used
+                try {
+                    com.bitchat.android.services.meshgraph.MeshGraphService.getInstance()
+                        .updateFromAnnouncement(myPeerID, nickname, directPeers, System.currentTimeMillis().toULong())
+                } catch (_: Exception) { }
+            } catch (_: Exception) { }
+            
             val announcePacket = BitchatPacket(
                 type = MessageType.ANNOUNCE.value,
                 ttl = MAX_TTL,
@@ -1069,12 +1094,26 @@ class BluetoothMeshService(private val context: Context) {
         
         // Create iOS-compatible IdentityAnnouncement with TLV encoding
         val announcement = IdentityAnnouncement(nickname, staticKey, signingKey)
-        val tlvPayload = announcement.encode()
+        var tlvPayload = announcement.encode()
         if (tlvPayload == null) {
             Log.e(TAG, "Failed to encode peer announcement as TLV")
             return
         }
 
+        // Append gossip TLV containing up to 10 direct neighbors (compact IDs)
+        try {
+            val directPeers = getDirectPeerIDsForGossip()
+            if (directPeers.isNotEmpty()) {
+                val gossip = com.bitchat.android.services.meshgraph.GossipTLV.encodeNeighbors(directPeers)
+                tlvPayload = tlvPayload + gossip
+            }
+            // Always update our own node in the mesh graph with the neighbor list we used
+            try {
+                com.bitchat.android.services.meshgraph.MeshGraphService.getInstance()
+                    .updateFromAnnouncement(myPeerID, nickname, directPeers, System.currentTimeMillis().toULong())
+            } catch (_: Exception) { }
+        } catch (_: Exception) { }
+        
         val packet = BitchatPacket(
             type = MessageType.ANNOUNCE.value,
             ttl = MAX_TTL,
@@ -1095,6 +1134,20 @@ class BluetoothMeshService(private val context: Context) {
         try { gossipSyncManager.onPublicPacketSeen(signedPacket) } catch (_: Exception) { }
     }
 
+    /**
+     * Collect up to 10 direct neighbors for gossip TLV.
+     */
+    private fun getDirectPeerIDsForGossip(): List<String> {
+        return try {
+            // Prefer verified peers that are currently marked as direct
+            val verified = peerManager.getVerifiedPeers()
+            val direct = verified.filter { it.value.isDirectConnection }.keys.toList()
+            direct.take(10)
+        } catch (_: Exception) {
+            emptyList()
+        }
+    }
+
     /**
      * Send leave announcement
      */
@@ -1277,21 +1330,38 @@ class BluetoothMeshService(private val context: Context) {
      */
     private fun signPacketBeforeBroadcast(packet: BitchatPacket): BitchatPacket {
         return try {
+            // Optionally compute and attach a source route for addressed packets
+            val withRoute = try {
+                val rec = packet.recipientID
+                if (rec != null && !rec.contentEquals(SpecialRecipients.BROADCAST)) {
+                    val dest = rec.joinToString("") { b -> "%02x".format(b) }
+                    val path = com.bitchat.android.services.meshgraph.RoutePlanner.shortestPath(myPeerID, dest)
+                    if (path != null && path.size >= 3) {
+                        // Exclude first (sender) and last (recipient); only intermediates
+                        val intermediates = path.subList(1, path.size - 1)
+                        val hopsBytes = intermediates.map { hexStringToByteArray(it) }
+                        Log.d(TAG, "✅ Signed packet type ${packet.type} (route ${hopsBytes.size} hops: $intermediates)")
+                        // Attach route and upgrade to v2 (required for HAS_ROUTE flag)
+                        packet.copy(route = hopsBytes, version = 2u)
+                    } else packet.copy(route = null)
+                } else packet
+            } catch (_: Exception) { packet }
+
             // Get the canonical packet data for signing (without signature)
-            val packetDataForSigning = packet.toBinaryDataForSigning()
+            val packetDataForSigning = withRoute.toBinaryDataForSigning()
             if (packetDataForSigning == null) {
                 Log.w(TAG, "Failed to encode packet type ${packet.type} for signing, sending unsigned")
-                return packet
+                return withRoute
             }
             
             // Sign the packet data using our signing key
             val signature = encryptionService.signData(packetDataForSigning)
             if (signature != null) {
                 Log.d(TAG, "✅ Signed packet type ${packet.type} (signature ${signature.size} bytes)")
-                packet.copy(signature = signature)
+                withRoute.copy(signature = signature)
             } else {
                 Log.w(TAG, "Failed to sign packet type ${packet.type}, sending unsigned")
-                packet
+                withRoute
             }
         } catch (e: Exception) {
             Log.w(TAG, "Error signing packet type ${packet.type}: ${e.message}, sending unsigned")

app/src/main/java/com/bitchat/android/mesh/BluetoothPacketBroadcaster.kt

@@ -68,7 +68,9 @@ class BluetoothPacketBroadcaster(
         incomingAddr: String?,
         toPeer: String?,
         toDeviceAddress: String,
-        ttl: UByte
+        ttl: UByte,
+        packetVersion: UByte = 1u,
+        routeInfo: String? = null
     ) {
         try {
             val fromNick = incomingPeer?.let { nicknameResolver?.invoke(it) }
@@ -80,7 +82,9 @@ class BluetoothPacketBroadcaster(
                 toPeerID = toPeer,
                 toNickname = toNick,
                 toDeviceAddress = toDeviceAddress,
-                previousHopPeerID = incomingPeer
+                previousHopPeerID = incomingPeer,
+                packetVersion = packetVersion,
+                routeInfo = routeInfo
             )
             // Keep the verbose relay message for human readability
             manager.logPacketRelayDetailed(
@@ -94,7 +98,9 @@ class BluetoothPacketBroadcaster(
                 toNickname = toNick,
                 toDeviceAddress = toDeviceAddress,
                 ttl = ttl,
-                isRelay = true
+                isRelay = true,
+                packetVersion = packetVersion,
+                routeInfo = routeInfo
             )
         } catch (_: Exception) { 
             // Silently ignore debug logging failures
@@ -221,17 +227,19 @@ class BluetoothPacketBroadcaster(
             TransferProgressManager.start(transferId, 1)
         }
         val typeName = MessageType.fromValue(packet.type)?.name ?: packet.type.toString()
+        val senderPeerID = routed.peerID ?: packet.senderID.toHexString()
         val incomingAddr = routed.relayAddress
         val incomingPeer = incomingAddr?.let { connectionTracker.addressPeerMap[it] }
-        val senderPeerID = routed.peerID ?: packet.senderID.toHexString()
         val senderNick = senderPeerID.let { pid -> nicknameResolver?.invoke(pid) }
+        val route = packet.route
+        val routeInfo = if (!route.isNullOrEmpty()) "routed: ${route.size} hops" else null
 
         // Prefer server-side subscriptions
         val serverTarget = connectionTracker.getSubscribedDevices()
             .firstOrNull { connectionTracker.addressPeerMap[it.address] == targetPeerID }
         if (serverTarget != null) {
             if (notifyDevice(serverTarget, data, gattServer, characteristic)) {
-                logPacketRelay(typeName, senderPeerID, senderNick, incomingPeer, incomingAddr, targetPeerID, serverTarget.address, packet.ttl)
+                logPacketRelay(typeName, senderPeerID, senderNick, incomingPeer, incomingAddr, targetPeerID, serverTarget.address, packet.ttl, packet.version, routeInfo)
                 if (transferId != null) {
                     TransferProgressManager.progress(transferId, 1, 1)
                     TransferProgressManager.complete(transferId, 1)
@@ -245,7 +253,7 @@ class BluetoothPacketBroadcaster(
             .firstOrNull { connectionTracker.addressPeerMap[it.device.address] == targetPeerID }
         if (clientTarget != null) {
             if (writeToDeviceConn(clientTarget, data)) {
-                logPacketRelay(typeName, senderPeerID, senderNick, incomingPeer, incomingAddr, targetPeerID, clientTarget.device.address, packet.ttl)
+                logPacketRelay(typeName, senderPeerID, senderNick, incomingPeer, incomingAddr, targetPeerID, clientTarget.device.address, packet.ttl, packet.version, routeInfo)
                 if (transferId != null) {
                     TransferProgressManager.progress(transferId, 1, 1)
                     TransferProgressManager.complete(transferId, 1)
@@ -284,6 +292,46 @@ class BluetoothPacketBroadcaster(
         }
     }
 
+    /**
+     * Targeted send to a specific peer (by peerID) if directly connected.
+     * Returns true if sent to at least one matching connection.
+     */
+    fun sendToPeer(
+        targetPeerID: String,
+        routed: RoutedPacket,
+        gattServer: BluetoothGattServer?,
+        characteristic: BluetoothGattCharacteristic?
+    ): Boolean {
+        val packet = routed.packet
+        val data = packet.toBinaryData() ?: return false
+        val typeName = MessageType.fromValue(packet.type)?.name ?: packet.type.toString()
+        val senderPeerID = routed.peerID ?: packet.senderID.toHexString()
+        val incomingAddr = routed.relayAddress
+        val incomingPeer = incomingAddr?.let { connectionTracker.addressPeerMap[it] }
+        val senderNick = senderPeerID.let { pid -> nicknameResolver?.invoke(pid) }
+
+        // Try server-side connections first
+        val targetDevice = connectionTracker.getSubscribedDevices()
+            .firstOrNull { connectionTracker.addressPeerMap[it.address] == targetPeerID }
+        if (targetDevice != null) {
+            if (notifyDevice(targetDevice, data, gattServer, characteristic)) {
+                logPacketRelay(typeName, senderPeerID, senderNick, incomingPeer, incomingAddr, targetPeerID, targetDevice.address, packet.ttl)
+                return true
+            }
+        }
+
+        // Try client-side connections next
+        val targetConn = connectionTracker.getConnectedDevices().values
+            .firstOrNull { connectionTracker.addressPeerMap[it.device.address] == targetPeerID }
+        if (targetConn != null) {
+            if (writeToDeviceConn(targetConn, data)) {
+                logPacketRelay(typeName, senderPeerID, senderNick, incomingPeer, incomingAddr, targetPeerID, targetConn.device.address, packet.ttl)
+                return true
+            }
+        }
+        return false
+    }
+    
     /**
      * Internal broadcast implementation - runs in serialized actor context
      */
@@ -299,6 +347,8 @@ class BluetoothPacketBroadcaster(
         val incomingAddr = routed.relayAddress
         val incomingPeer = incomingAddr?.let { connectionTracker.addressPeerMap[it] }
         val senderNick = senderPeerID.let { pid -> nicknameResolver?.invoke(pid) }
+        val route = packet.route
+        val routeInfo = if (!route.isNullOrEmpty()) "routed: ${route.size} hops" else null
         
         if (packet.recipientID != SpecialRecipients.BROADCAST) {
             val recipientID = packet.recipientID?.let {
@@ -314,7 +364,7 @@ class BluetoothPacketBroadcaster(
                 Log.d(TAG, "Send packet type ${packet.type} directly to target device for recipient $recipientID: ${targetDevice.address}")
                 if (notifyDevice(targetDevice, data, gattServer, characteristic)) {
                     val toPeer = connectionTracker.addressPeerMap[targetDevice.address]
-                    logPacketRelay(typeName, senderPeerID, senderNick, incomingPeer, incomingAddr, toPeer, targetDevice.address, packet.ttl)
+                    logPacketRelay(typeName, senderPeerID, senderNick, incomingPeer, incomingAddr, toPeer, targetDevice.address, packet.ttl, packet.version, routeInfo)
                     return  // Sent, no need to continue
                 }
             }
@@ -328,7 +378,7 @@ class BluetoothPacketBroadcaster(
                 Log.d(TAG, "Send packet type ${packet.type} directly to target client connection for recipient $recipientID: ${targetDeviceConn.device.address}")
                 if (writeToDeviceConn(targetDeviceConn, data)) {
                     val toPeer = connectionTracker.addressPeerMap[targetDeviceConn.device.address]
-                    logPacketRelay(typeName, senderPeerID, senderNick, incomingPeer, incomingAddr, toPeer, targetDeviceConn.device.address, packet.ttl)
+                    logPacketRelay(typeName, senderPeerID, senderNick, incomingPeer, incomingAddr, toPeer, targetDeviceConn.device.address, packet.ttl, packet.version, routeInfo)
                     return  // Sent, no need to continue
                 }
             }
@@ -338,7 +388,7 @@ class BluetoothPacketBroadcaster(
         val subscribedDevices = connectionTracker.getSubscribedDevices()
         val connectedDevices = connectionTracker.getConnectedDevices()
         
-        Log.i(TAG, "Broadcasting packet type ${packet.type} to ${subscribedDevices.size} server + ${connectedDevices.size} client connections")
+        Log.i(TAG, "Broadcasting packet v${packet.version} type ${packet.type} to ${subscribedDevices.size} server + ${connectedDevices.size} client connections")
 
         val senderID = String(packet.senderID).replace("\u0000", "")        
         
@@ -355,7 +405,7 @@ class BluetoothPacketBroadcaster(
             val sent = notifyDevice(device, data, gattServer, characteristic)
             if (sent) {
                 val toPeer = connectionTracker.addressPeerMap[device.address]
-                logPacketRelay(typeName, senderPeerID, senderNick, incomingPeer, incomingAddr, toPeer, device.address, packet.ttl)
+                logPacketRelay(typeName, senderPeerID, senderNick, incomingPeer, incomingAddr, toPeer, device.address, packet.ttl, packet.version, routeInfo)
             }
         }
         
@@ -373,7 +423,7 @@ class BluetoothPacketBroadcaster(
                 val sent = writeToDeviceConn(deviceConn, data)
                 if (sent) {
                     val toPeer = connectionTracker.addressPeerMap[deviceConn.device.address]
-                    logPacketRelay(typeName, senderPeerID, senderNick, incomingPeer, incomingAddr, toPeer, deviceConn.device.address, packet.ttl)
+                    logPacketRelay(typeName, senderPeerID, senderNick, incomingPeer, incomingAddr, toPeer, deviceConn.device.address, packet.ttl, packet.version, routeInfo)
                 }
             }
         }

app/src/main/java/com/bitchat/android/mesh/FragmentManager.kt

@@ -77,8 +77,31 @@ class FragmentManager {
         val fragmentID = FragmentPayload.generateFragmentID()
         
         // iOS: stride(from: 0, to: fullData.count, by: maxFragmentSize)
-        val fragmentChunks = stride(0, fullData.size, MAX_FRAGMENT_SIZE) { offset ->
+        // Calculate dynamic fragment size to fit in MTU (512)
-            val endOffset = minOf(offset + MAX_FRAGMENT_SIZE, fullData.size)
+        // Packet = Header + Sender + Recipient + Route + FragmentHeader + Payload + PaddingBuffer
+        val hasRoute = packet.route != null
+        val version = if (hasRoute) 2 else 1
+        val headerSize = if (version == 2) 15 else 13
+        val senderSize = 8
+        val recipientSize = if (packet.recipientID != null) 8 else 0
+        // Route: 1 byte count + 8 bytes per hop
+        val routeSize = if (hasRoute) (1 + (packet.route?.size ?: 0) * 8) else 0
+        val fragmentHeaderSize = 13 // FragmentPayload header
+        val paddingBuffer = 16 // MessagePadding.optimalBlockSize adds 16 bytes overhead
+
+        // 512 - Overhead
+        val packetOverhead = headerSize + senderSize + recipientSize + routeSize + fragmentHeaderSize + paddingBuffer
+        val maxDataSize = (512 - packetOverhead).coerceAtMost(MAX_FRAGMENT_SIZE)
+        
+        if (maxDataSize <= 0) {
+            Log.e(TAG, "❌ Calculated maxDataSize is non-positive ($maxDataSize). Route too large?")
+            return emptyList()
+        }
+
+        Log.d(TAG, "📏 Dynamic fragment size: $maxDataSize (MAX: $MAX_FRAGMENT_SIZE, Overhead: $packetOverhead)")
+
+        val fragmentChunks = stride(0, fullData.size, maxDataSize) { offset ->
+            val endOffset = minOf(offset + maxDataSize, fullData.size)
             fullData.sliceArray(offset..<endOffset)
         }
         
@@ -98,13 +121,16 @@ class FragmentManager {
             )
             
             // iOS: MessageType.fragment.rawValue (single fragment type)
+            // Fix: Fragments must inherit source route and use v2 if routed
             val fragmentPacket = BitchatPacket(
+                version = if (packet.route != null) 2u else 1u,
                 type = MessageType.FRAGMENT.value,
                 ttl = packet.ttl,
                 senderID = packet.senderID,
                 recipientID = packet.recipientID,
                 timestamp = packet.timestamp,
                 payload = fragmentPayload.encode(),
+                route = packet.route,
                 signature = null // iOS: signature: nil
             )
             

app/src/main/java/com/bitchat/android/mesh/MessageHandler.kt

@@ -286,6 +286,13 @@ class MessageHandler(private val myPeerID: String, private val appContext: andro
             previousPeerID = null
         )
         
+        // Update mesh graph from gossip neighbors (only if TLV present)
+        try {
+            val neighborsOrNull = com.bitchat.android.services.meshgraph.GossipTLV.decodeNeighborsFromAnnouncementPayload(packet.payload)
+            com.bitchat.android.services.meshgraph.MeshGraphService.getInstance()
+                .updateFromAnnouncement(peerID, nickname, neighborsOrNull, packet.timestamp)
+        } catch (_: Exception) { }
+
         Log.d(TAG, "✅ Processed verified TLV announce: stored identity for $peerID")
         return isFirstAnnounce
     }

app/src/main/java/com/bitchat/android/mesh/PacketProcessor.kt

@@ -112,6 +112,9 @@ class PacketProcessor(private val myPeerID: String) {
             override fun broadcastPacket(routed: RoutedPacket) {
                 delegate?.relayPacket(routed)
             }
+            override fun sendToPeer(peerID: String, routed: RoutedPacket): Boolean {
+                return delegate?.sendToPeer(peerID, routed) ?: false
+            }
         }
     }
     
@@ -323,4 +326,5 @@ interface PacketProcessorDelegate {
     fun sendAnnouncementToPeer(peerID: String)
     fun sendCachedMessages(peerID: String)
     fun relayPacket(routed: RoutedPacket)
+    fun sendToPeer(peerID: String, routed: RoutedPacket): Boolean
 }

app/src/main/java/com/bitchat/android/mesh/PacketRelayManager.kt

@@ -65,9 +65,40 @@ class PacketRelayManager(private val myPeerID: String) {
         val relayPacket = packet.copy(ttl = (packet.ttl - 1u).toUByte())
         Log.d(TAG, "Decremented TTL from ${packet.ttl} to ${relayPacket.ttl}")
         
+        // Source-based routing: if route is set and includes us, try targeted next-hop forwarding
+        val route = relayPacket.route
+        if (!route.isNullOrEmpty()) {
+            // Check for duplicate hops to prevent routing loops
+            if (route.map { it.toHexString() }.toSet().size < route.size) {
+                Log.w(TAG, "Packet with duplicate hops dropped")
+                return
+            }
+            val myIdBytes = hexStringToPeerBytes(myPeerID)
+            val index = route.indexOfFirst { it.contentEquals(myIdBytes) }
+            if (index >= 0) {
+                val nextHopIdHex: String? = run {
+                    val nextIndex = index + 1
+                    if (nextIndex < route.size) {
+                        route[nextIndex].toHexString()
+                    } else {
+                        // We are the last intermediate; try final recipient as next hop
+                        relayPacket.recipientID?.toHexString()
+                    }
+                }
+                if (nextHopIdHex != null) {
+                    val success = try { delegate?.sendToPeer(nextHopIdHex, RoutedPacket(relayPacket, peerID, routed.relayAddress)) } catch (_: Exception) { false } ?: false
+                    if (success) {
+                        Log.i(TAG, "📦 Source-route relay: ${peerID.take(8)} -> ${nextHopIdHex.take(8)} (type ${'$'}{packet.type}, TTL ${'$'}{relayPacket.ttl})")
+                        return
+                    } else {
+                        Log.w(TAG, "Source-route next hop ${nextHopIdHex.take(8)} not directly connected; falling back to broadcast")
+                    }
+                }
+            }
+        }
+
         // Apply relay logic based on packet type and debug switch
         val shouldRelay = isRelayEnabled() && shouldRelayPacket(relayPacket, peerID)
-        
         if (shouldRelay) {
             relayPacket(RoutedPacket(relayPacket, peerID, routed.relayAddress))
         } else {
@@ -170,4 +201,17 @@ interface PacketRelayManagerDelegate {
     
     // Packet operations
     fun broadcastPacket(routed: RoutedPacket)
+    fun sendToPeer(peerID: String, routed: RoutedPacket): Boolean
+}
+
+private fun hexStringToPeerBytes(hex: String): ByteArray {
+    val result = ByteArray(8)
+    var idx = 0
+    var out = 0
+    while (idx + 1 < hex.length && out < 8) {
+        val b = hex.substring(idx, idx + 2).toIntOrNull(16)?.toByte() ?: 0
+        result[out++] = b
+        idx += 2
+    }
+    return result
 }

app/src/main/java/com/bitchat/android/protocol/BinaryProtocol.kt

@@ -59,7 +59,8 @@ data class BitchatPacket(
     val timestamp: ULong,
     val payload: ByteArray,
     var signature: ByteArray? = null,  // Changed from val to var for packet signing
-    var ttl: UByte
+    var ttl: UByte,
+    var route: List<ByteArray>? = null // Optional source route: ordered list of peerIDs (8 bytes each), not including sender and final recipient
 ) : Parcelable {
 
     constructor(
@@ -97,6 +98,7 @@ data class BitchatPacket(
             timestamp = timestamp,
             payload = payload,
             signature = null, // Remove signature for signing
+            route = route,
             ttl = com.bitchat.android.util.AppConstants.SYNC_TTL_HOPS // Use fixed TTL=0 for signing to ensure relay compatibility
         )
         return BinaryProtocol.encode(unsignedPacket)
@@ -149,6 +151,11 @@ data class BitchatPacket(
             if (!signature.contentEquals(other.signature)) return false
         } else if (other.signature != null) return false
         if (ttl != other.ttl) return false
+        if (route != null || other.route != null) {
+            val a = route?.map { it.toList() } ?: emptyList()
+            val b = other.route?.map { it.toList() } ?: emptyList()
+            if (a != b) return false
+        }
 
         return true
     }
@@ -162,6 +169,7 @@ data class BitchatPacket(
         result = 31 * result + payload.contentHashCode()
         result = 31 * result + (signature?.contentHashCode() ?: 0)
         result = 31 * result + ttl.hashCode()
+        result = 31 * result + (route?.fold(1) { acc, bytes -> 31 * acc + bytes.contentHashCode() } ?: 0)
         return result
     }
 }
@@ -180,6 +188,7 @@ object BinaryProtocol {
         const val HAS_RECIPIENT: UByte = 0x01u
         const val HAS_SIGNATURE: UByte = 0x02u
         const val IS_COMPRESSED: UByte = 0x04u
+        const val HAS_ROUTE: UByte = 0x08u
     }
 
     private fun getHeaderSize(version: UByte): Int {
@@ -193,12 +202,12 @@ object BinaryProtocol {
         try {
             // Try to compress payload if beneficial
             var payload = packet.payload
-            var originalPayloadSize: UShort? = null
+            var originalPayloadSize: Int? = null
             var isCompressed = false
             
             if (CompressionUtil.shouldCompress(payload)) {
                 CompressionUtil.compress(payload)?.let { compressedPayload ->
-                    originalPayloadSize = payload.size.toUShort()
+                    originalPayloadSize = payload.size
                     payload = compressedPayload
                     isCompressed = true
                 }
@@ -208,8 +217,12 @@ object BinaryProtocol {
             val headerSize = getHeaderSize(packet.version)
             val recipientBytes = if (packet.recipientID != null) RECIPIENT_ID_SIZE else 0
             val signatureBytes = if (packet.signature != null) SIGNATURE_SIZE else 0
-            val payloadBytes = payload.size + if (isCompressed) 2 else 0
+            val sizeFieldBytes = if (isCompressed) (if (packet.version >= 2u.toUByte()) 4 else 2) else 0
-            val capacity = headerSize + SENDER_ID_SIZE + recipientBytes + payloadBytes + signatureBytes + 16 // small slack
+            val payloadBytes = payload.size + sizeFieldBytes
+            val routeBytes = if (!packet.route.isNullOrEmpty() && packet.version >= 2u.toUByte()) {
+                1 + (packet.route!!.size.coerceAtMost(255) * SENDER_ID_SIZE)
+            } else 0
+            val capacity = headerSize + SENDER_ID_SIZE + recipientBytes + payloadBytes + signatureBytes + routeBytes + 16 // small slack
             val buffer = ByteBuffer.allocate(capacity.coerceAtLeast(512)).apply { order(ByteOrder.BIG_ENDIAN) }
             
             // Header
@@ -231,10 +244,14 @@ object BinaryProtocol {
             if (isCompressed) {
                 flags = flags or Flags.IS_COMPRESSED
             }
+            // HAS_ROUTE is only supported for v2+ packets
+            if (!packet.route.isNullOrEmpty() && packet.version >= 2u.toUByte()) {
+                flags = flags or Flags.HAS_ROUTE
+            }
             buffer.put(flags.toByte())
             
             // Payload length (2 or 4 bytes, big-endian) - includes original size if compressed
-            val payloadDataSize = payload.size + if (isCompressed) 2 else 0
+            val payloadDataSize = payload.size + sizeFieldBytes
             if (packet.version >= 2u.toUByte()) {
                 buffer.putInt(payloadDataSize)  // 4 bytes for v2+
             } else {
@@ -257,13 +274,27 @@ object BinaryProtocol {
                 }
             }
 
+            // Route (optional, v2+ only): 1 byte count + N*8 bytes
+            if (packet.version >= 2u.toUByte() && !packet.route.isNullOrEmpty()) {
+                packet.route?.let { routeList ->
+                    val cleaned = routeList.map { bytes -> bytes.take(SENDER_ID_SIZE).toByteArray().let { if (it.size < SENDER_ID_SIZE) it + ByteArray(SENDER_ID_SIZE - it.size) else it } }
+                    val count = cleaned.size.coerceAtMost(255)
+                    buffer.put(count.toByte())
+                    cleaned.take(count).forEach { hop -> buffer.put(hop) }
+                }
+            }
+            
             // Payload (with original size prepended if compressed)
             if (isCompressed) {
                 val originalSize = originalPayloadSize
                 if (originalSize != null) {
+                    if (packet.version >= 2u.toUByte()) {
+                        buffer.putInt(originalSize.toInt())
+                    } else {
                         buffer.putShort(originalSize.toShort())
                     }
                 }
+            }
             buffer.put(payload)
             
             // Signature (if present)
@@ -324,6 +355,8 @@ object BinaryProtocol {
             val hasRecipient = (flags and Flags.HAS_RECIPIENT) != 0u.toUByte()
             val hasSignature = (flags and Flags.HAS_SIGNATURE) != 0u.toUByte()
             val isCompressed = (flags and Flags.IS_COMPRESSED) != 0u.toUByte()
+            // HAS_ROUTE is only valid for v2+ packets; ignore the flag for v1
+            val hasRoute = (version >= 2u.toUByte()) && (flags and Flags.HAS_ROUTE) != 0u.toUByte()
 
             // Payload length - version-dependent (2 or 4 bytes)
             val payloadLength = if (version >= 2u.toUByte()) {
@@ -335,6 +368,22 @@ object BinaryProtocol {
             // Calculate expected total size
             var expectedSize = headerSize + SENDER_ID_SIZE + payloadLength.toInt()
             if (hasRecipient) expectedSize += RECIPIENT_ID_SIZE
+            var routeCount = 0
+            if (hasRoute) {
+                // Peek count (1 byte) without consuming buffer for now
+                // The buffer is currently positioned at the start of SenderID (after fixed header)
+                // We must skip SenderID and RecipientID (if present) to find the route count
+                val currentPos = buffer.position()
+                var routeOffset = currentPos + SENDER_ID_SIZE
+                if (hasRecipient) {
+                    routeOffset += RECIPIENT_ID_SIZE
+                }
+
+                if (raw.size >= routeOffset + 1) {
+                    routeCount = raw[routeOffset].toUByte().toInt()
+                }
+                expectedSize += 1 + (routeCount * SENDER_ID_SIZE)
+            }
             if (hasSignature) expectedSize += SIGNATURE_SIZE
 
             if (raw.size < expectedSize) return null
@@ -350,16 +399,47 @@ object BinaryProtocol {
                 recipientBytes
             } else null
             
+            // Route (optional)
+            val route: List<ByteArray>? = if (hasRoute) {
+                val count = buffer.get().toUByte().toInt()
+                if (count == 0) {
+                    null // Treat empty route list as null to enforce canonical representation
+                } else {
+                    val hops = mutableListOf<ByteArray>()
+                    repeat(count) {
+                        val hop = ByteArray(SENDER_ID_SIZE)
+                        buffer.get(hop)
+                        hops.add(hop)
+                    }
+                    hops
+                }
+            } else null
+
             // Payload
             val payload = if (isCompressed) {
-                // First 2 bytes are original size
+                val lengthFieldBytes = if (version >= 2u.toUByte()) 4 else 2
-                if (payloadLength.toInt() < 2) return null
+                if (payloadLength.toInt() < lengthFieldBytes) return null
-                val originalSize = buffer.getShort().toInt()
+                
+                val originalSize = if (version >= 2u.toUByte()) {
+                    buffer.getInt()
+                } else {
+                    buffer.getShort().toUShort().toInt()
+                }
                 
                 // Compressed payload
-                val compressedPayload = ByteArray(payloadLength.toInt() - 2)
+                val compressedSize = payloadLength.toInt() - lengthFieldBytes
+                val compressedPayload = ByteArray(compressedSize)
                 buffer.get(compressedPayload)
 
+                // Security check: Compression bomb protection
+                if (compressedSize > 0) {
+                    val ratio = originalSize.toDouble() / compressedSize.toDouble()
+                    if (ratio > 50_000.0) {
+                        Log.w("BinaryProtocol", "🚫 Suspicious compression ratio: ${ratio}:1")
+                        return null
+                    }
+                }
+                
                 // Decompress
                 CompressionUtil.decompress(compressedPayload, originalSize) ?: return null
             } else {
@@ -383,7 +463,8 @@ object BinaryProtocol {
                 timestamp = timestamp,
                 payload = payload,
                 signature = signature,
-                ttl = ttl
+                ttl = ttl,
+                route = route
             )
             
         } catch (e: Exception) {

app/src/main/java/com/bitchat/android/services/meshgraph/GossipTLV.kt

@@ -0,0 +1,77 @@
+package com.bitchat.android.services.meshgraph
+
+import android.util.Log
+
+/**
+ * Gossip TLV helpers for embedding direct neighbor peer IDs in ANNOUNCE payloads.
+ * Uses compact TLV: [type=0x04][len=1 byte][value=N*8 bytes of peerIDs]
+ */
+object GossipTLV {
+    // TLV type for a compact list of direct neighbor peerIDs (each 8 bytes)
+    const val DIRECT_NEIGHBORS_TYPE: UByte = 0x04u
+
+    /**
+     * Encode up to 10 unique peerIDs (hex string up to 16 chars) as TLV value.
+     */
+    fun encodeNeighbors(peerIDs: List<String>): ByteArray {
+        val unique = peerIDs.distinct().take(10)
+        val valueBytes = unique.flatMap { id -> hexStringPeerIdTo8Bytes(id).toList() }.toByteArray()
+        if (valueBytes.size > 255) {
+            // Safety check, though 10*8 = 80 bytes, so well under 255
+            Log.w("GossipTLV", "Neighbors value exceeds 255, truncating")
+        }
+        return byteArrayOf(DIRECT_NEIGHBORS_TYPE.toByte(), valueBytes.size.toByte()) + valueBytes
+    }
+
+    /**
+     * Scan a TLV-encoded announce payload and extract neighbor peerIDs.
+     * Returns null if the TLV is not present at all; returns an empty list if present with length 0.
+     */
+    fun decodeNeighborsFromAnnouncementPayload(payload: ByteArray): List<String>? {
+        val result = mutableListOf<String>()
+        var offset = 0
+        while (offset + 2 <= payload.size) {
+            val type = payload[offset].toUByte()
+            val len = payload[offset + 1].toUByte().toInt()
+            offset += 2
+            if (offset + len > payload.size) break
+            val value = payload.sliceArray(offset until offset + len)
+            offset += len
+
+            if (type == DIRECT_NEIGHBORS_TYPE) {
+                // Value is N*8 bytes of peer IDs
+                var pos = 0
+                while (pos + 8 <= value.size) {
+                    val idBytes = value.sliceArray(pos until pos + 8)
+                    result.add(bytesToPeerIdHex(idBytes))
+                    pos += 8
+                }
+                return result // present (possibly empty)
+            }
+        }
+        // Not present
+        return null
+    }
+
+    private fun hexStringPeerIdTo8Bytes(hexString: String): ByteArray {
+        val clean = hexString.lowercase().take(16)
+        val result = ByteArray(8) { 0 }
+        var idx = 0
+        var out = 0
+        while (idx + 1 < clean.length && out < 8) {
+            val byteStr = clean.substring(idx, idx + 2)
+            val b = byteStr.toIntOrNull(16)?.toByte() ?: 0
+            result[out++] = b
+            idx += 2
+        }
+        return result
+    }
+
+    private fun bytesToPeerIdHex(bytes: ByteArray): String {
+        val sb = StringBuilder()
+        for (b in bytes.take(8)) {
+            sb.append(String.format("%02x", b))
+        }
+        return sb.toString()
+    }
+}

app/src/main/java/com/bitchat/android/services/meshgraph/MeshGraphService.kt

@@ -0,0 +1,123 @@
+package com.bitchat.android.services.meshgraph
+
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.flow.asStateFlow
+import java.util.concurrent.ConcurrentHashMap
+
+/**
+ * Maintains an internal graph of the mesh based on gossip.
+ * Nodes are peers (peerID), edges are direct connections.
+ */
+class MeshGraphService private constructor() {
+    data class GraphNode(val peerID: String, val nickname: String?)
+    data class GraphEdge(val a: String, val b: String, val isConfirmed: Boolean, val confirmedBy: String? = null)
+    data class GraphSnapshot(val nodes: List<GraphNode>, val edges: List<GraphEdge>)
+
+    // Map peerID -> nickname (may be null if unknown)
+    private val nicknames = ConcurrentHashMap<String, String?>()
+    // Announcements: peerID -> set of neighbor peerIDs that *this* peer claims to see
+    private val announcements = ConcurrentHashMap<String, Set<String>>()
+    // Latest announcement timestamp per peer (ULong from packet)
+    private val lastUpdate = ConcurrentHashMap<String, ULong>()
+
+    private val _graphState = MutableStateFlow(GraphSnapshot(emptyList(), emptyList()))
+    val graphState: StateFlow<GraphSnapshot> = _graphState.asStateFlow()
+
+    /**
+     * Update graph from a verified announcement.
+     * Replaces previous neighbors for origin if this is newer (by timestamp).
+     */
+    fun updateFromAnnouncement(originPeerID: String, originNickname: String?, neighborsOrNull: List<String>?, timestamp: ULong) {
+        synchronized(this) {
+            // Always update nickname if provided
+            if (originNickname != null) nicknames[originPeerID] = originNickname
+
+            // If no neighbors TLV present, do not modify edges or timestamps
+            if (neighborsOrNull == null) {
+                publishSnapshot()
+                return
+            }
+
+            // Newer-only replacement per origin (based on TLV-bearing announcements only)
+            val prevTs = lastUpdate[originPeerID]
+            if (prevTs != null && prevTs >= timestamp) {
+                // Older or equal TLV-bearing update: ignore
+                return
+            }
+            lastUpdate[originPeerID] = timestamp
+
+            // Update what originPeerID announces
+            // Filter out self-loops just in case
+            val newSet = neighborsOrNull.distinct().take(10).filter { it != originPeerID }.toSet()
+            announcements[originPeerID] = newSet
+
+            publishSnapshot()
+        }
+    }
+
+    fun updateNickname(peerID: String, nickname: String?) {
+        if (nickname == null) return
+        nicknames[peerID] = nickname
+        publishSnapshot()
+    }
+
+    /**
+     * Remove a peer from the graph completely (e.g. when stale/offline).
+     */
+    fun removePeer(peerID: String) {
+        synchronized(this) {
+            nicknames.remove(peerID)
+            announcements.remove(peerID)
+            lastUpdate.remove(peerID)
+            publishSnapshot()
+        }
+    }
+
+    private fun publishSnapshot() {
+        // Collect all known nodes from nicknames and announcements
+        val allNodes = mutableSetOf<String>()
+        allNodes.addAll(nicknames.keys)
+        announcements.forEach { (origin, neighbors) ->
+            allNodes.add(origin)
+            allNodes.addAll(neighbors)
+        }
+
+        val nodeList = allNodes.map { GraphNode(it, nicknames[it]) }.sortedBy { it.peerID }
+
+        val edges = mutableListOf<GraphEdge>()
+        val processedPairs = mutableSetOf<Pair<String, String>>()
+
+        // We only care about connections that exist in at least one direction.
+        // So iterating through all entries in `announcements` covers every declared edge.
+        announcements.forEach { (source, targets) ->
+            targets.forEach { target ->
+                val pair = if (source <= target) source to target else target to source
+                if (processedPairs.add(pair)) {
+                    // This is a new pair we haven't evaluated yet
+                    val (a, b) = pair
+                    val aAnnouncesB = announcements[a]?.contains(b) == true
+                    val bAnnouncesA = announcements[b]?.contains(a) == true
+
+                    if (aAnnouncesB && bAnnouncesA) {
+                        edges.add(GraphEdge(a, b, isConfirmed = true))
+                    } else if (aAnnouncesB) {
+                        edges.add(GraphEdge(a, b, isConfirmed = false, confirmedBy = a))
+                    } else if (bAnnouncesA) {
+                        edges.add(GraphEdge(a, b, isConfirmed = false, confirmedBy = b))
+                    }
+                }
+            }
+        }
+
+        val sortedEdges = edges.sortedWith(compareBy({ it.a }, { it.b }))
+        _graphState.value = GraphSnapshot(nodeList, sortedEdges)
+    }
+
+    companion object {
+        @Volatile private var INSTANCE: MeshGraphService? = null
+        fun getInstance(): MeshGraphService = INSTANCE ?: synchronized(this) {
+            INSTANCE ?: MeshGraphService().also { INSTANCE = it }
+        }
+    }
+}

app/src/main/java/com/bitchat/android/services/meshgraph/RoutePlanner.kt

@@ -0,0 +1,68 @@
+package com.bitchat.android.services.meshgraph
+
+import android.util.Log
+import java.util.PriorityQueue
+
+/**
+ * Computes shortest paths on the current mesh graph snapshot using Dijkstra.
+ * Assumes unit edge weights.
+ */
+object RoutePlanner {
+    private const val TAG = "RoutePlanner"
+
+    /**
+     * Return full path [src, ..., dst] if reachable, else null.
+     */
+    fun shortestPath(src: String, dst: String): List<String>? {
+        if (src == dst) return listOf(src)
+        val snapshot = MeshGraphService.getInstance().graphState.value
+        val neighbors = mutableMapOf<String, MutableSet<String>>()
+        
+        // Only consider confirmed edges for routing
+        snapshot.edges.filter { it.isConfirmed }.forEach { e ->
+            neighbors.getOrPut(e.a) { mutableSetOf() }.add(e.b)
+            neighbors.getOrPut(e.b) { mutableSetOf() }.add(e.a)
+        }
+        // Ensure nodes known even if isolated
+        snapshot.nodes.forEach { n -> neighbors.putIfAbsent(n.peerID, mutableSetOf()) }
+
+        if (!neighbors.containsKey(src) || !neighbors.containsKey(dst)) return null
+
+        val dist = mutableMapOf<String, Int>()
+        val prev = mutableMapOf<String, String?>()
+        val pq = PriorityQueue<Pair<String, Int>>(compareBy { it.second })
+
+        neighbors.keys.forEach { v ->
+            dist[v] = if (v == src) 0 else Int.MAX_VALUE
+            prev[v] = null
+        }
+        pq.add(src to 0)
+
+        while (pq.isNotEmpty()) {
+            val top = pq.poll() ?: break
+            val (u, d) = top
+            if (d > (dist[u] ?: Int.MAX_VALUE)) continue
+            if (u == dst) break
+            neighbors[u]?.forEach { v ->
+                val alt = d + 1
+                if (alt < (dist[v] ?: Int.MAX_VALUE)) {
+                    dist[v] = alt
+                    prev[v] = u
+                    pq.add(v to alt)
+                }
+            }
+        }
+
+        if ((dist[dst] ?: Int.MAX_VALUE) == Int.MAX_VALUE) return null
+
+        val path = mutableListOf<String>()
+        var cur: String? = dst
+        while (cur != null) {
+            path.add(cur)
+            cur = prev[cur]
+        }
+        path.reverse()
+        Log.d(TAG, "Computed path $path")
+        return path
+    }
+}

app/src/main/java/com/bitchat/android/ui/debug/DebugSettingsManager.kt

@@ -418,7 +418,9 @@ class DebugSettingsManager private constructor() {
         toNickname: String?,
         toDeviceAddress: String?,
         ttl: UByte?,
-        isRelay: Boolean = true
+        isRelay: Boolean = true,
+        packetVersion: UByte = 1u,
+        routeInfo: String? = null
     ) {
         // Build message only if verbose logging is enabled, but always update stats
         val senderLabel = when {
@@ -441,18 +443,20 @@ class DebugSettingsManager private constructor() {
         val fromAddr = fromDeviceAddress ?: "?"
         val toAddr = toDeviceAddress ?: "?"
         val ttlStr = ttl?.toString() ?: "?"
+        val routeStr = if (routeInfo != null) " $routeInfo" else ""
 
         if (verboseLoggingEnabled.value) {
             if (isRelay) {
+                // Relay: show [previousPeer] -> [nextPeer]
                 addDebugMessage(
                     DebugMessage.RelayEvent(
-                        "♻️ Relayed $packetType by $senderLabel from $fromName (${fromPeerID ?: "?"}, $fromAddr) to $toName (${toPeerID ?: "?"}, $toAddr) with TTL $ttlStr"
+                        "♻️ Relayed v$packetVersion $packetType by $senderLabel from $fromName (${fromPeerID ?: "?"}, $fromAddr) to $toName (${toPeerID ?: "?"}, $toAddr) with TTL $ttlStr$routeStr"
                     )
                 )
             } else {
                 addDebugMessage(
                     DebugMessage.PacketEvent(
-                        "📤 Sent $packetType by $senderLabel to $toName (${toPeerID ?: "?"}, $toAddr) with TTL $ttlStr"
+                        "📤 Sent v$packetVersion $packetType by $senderLabel to $toName (${toPeerID ?: "?"}, $toAddr) with TTL $ttlStr$routeStr"
                     )
                 )
             }
@@ -462,10 +466,11 @@ class DebugSettingsManager private constructor() {
     }
 
     // Explicit incoming/outgoing logging to avoid double counting
-    fun logIncoming(packetType: String, fromPeerID: String?, fromNickname: String?, fromDeviceAddress: String?) {
+    fun logIncoming(packetType: String, fromPeerID: String?, fromNickname: String?, fromDeviceAddress: String?, packetVersion: UByte = 1u, routeInfo: String? = null) {
         if (verboseLoggingEnabled.value) {
             val who = fromNickname ?: fromPeerID ?: "unknown"
-            addDebugMessage(DebugMessage.PacketEvent("📥 Incoming $packetType from $who (${fromPeerID ?: "?"}, ${fromDeviceAddress ?: "?"})"))
+            val routeStr = if (routeInfo != null) " $routeInfo" else ""
+            addDebugMessage(DebugMessage.PacketEvent("📥 Incoming v$packetVersion $packetType from $who (${fromPeerID ?: "?"}, ${fromDeviceAddress ?: "?"})$routeStr"))
         }
         val now = System.currentTimeMillis()
         val visible = _debugSheetVisible.value
@@ -489,10 +494,11 @@ class DebugSettingsManager private constructor() {
         if (visible) updateRelayStatsFromTimestamps()
     }
 
-    fun logOutgoing(packetType: String, toPeerID: String?, toNickname: String?, toDeviceAddress: String?, previousHopPeerID: String? = null) {
+    fun logOutgoing(packetType: String, toPeerID: String?, toNickname: String?, toDeviceAddress: String?, previousHopPeerID: String? = null, packetVersion: UByte = 1u, routeInfo: String? = null) {
         if (verboseLoggingEnabled.value) {
             val who = toNickname ?: toPeerID ?: "unknown"
-            addDebugMessage(DebugMessage.PacketEvent("📤 Outgoing $packetType to $who (${toPeerID ?: "?"}, ${toDeviceAddress ?: "?"})"))
+            val routeStr = if (routeInfo != null) " $routeInfo" else ""
+            addDebugMessage(DebugMessage.PacketEvent("📤 Outgoing v$packetVersion $packetType to $who (${toPeerID ?: "?"}, ${toDeviceAddress ?: "?"})$routeStr"))
         }
         val now = System.currentTimeMillis()
         val visible = _debugSheetVisible.value

app/src/main/java/com/bitchat/android/ui/debug/DebugSettingsSheet.kt

@@ -25,12 +25,120 @@ import androidx.compose.ui.unit.dp
 import androidx.compose.ui.unit.sp
 import androidx.compose.ui.draw.rotate
 import com.bitchat.android.mesh.BluetoothMeshService
+import com.bitchat.android.services.meshgraph.MeshGraphService
 import kotlinx.coroutines.launch
+import androidx.compose.ui.graphics.toArgb
+import androidx.compose.ui.graphics.drawscope.drawIntoCanvas
+import androidx.compose.ui.graphics.nativeCanvas
 import androidx.compose.ui.res.stringResource
 import com.bitchat.android.R
 import androidx.compose.ui.platform.LocalContext
 import com.bitchat.android.core.ui.component.sheet.BitchatBottomSheet
 
+@Composable
+fun MeshTopologySection() {
+    val colorScheme = MaterialTheme.colorScheme
+    val graphService = remember { MeshGraphService.getInstance() }
+    val snapshot by graphService.graphState.collectAsState()
+
+    Surface(shape = RoundedCornerShape(12.dp), color = colorScheme.surfaceVariant.copy(alpha = 0.2f)) {
+        Column(Modifier.padding(16.dp), verticalArrangement = Arrangement.spacedBy(8.dp)) {
+            Row(verticalAlignment = Alignment.CenterVertically, horizontalArrangement = Arrangement.spacedBy(8.dp)) {
+                Icon(Icons.Filled.SettingsEthernet, contentDescription = null, tint = Color(0xFF8E8E93))
+                Text("mesh topology", fontFamily = FontFamily.Monospace, fontSize = 14.sp, fontWeight = FontWeight.Medium)
+            }
+            val nodes = snapshot.nodes
+            val edges = snapshot.edges
+            val empty = nodes.isEmpty()
+            if (empty) {
+                Text("no gossip yet", fontFamily = FontFamily.Monospace, fontSize = 11.sp, color = colorScheme.onSurface.copy(alpha = 0.6f))
+            } else {
+                androidx.compose.foundation.Canvas(Modifier.fillMaxWidth().height(220.dp).background(colorScheme.surface.copy(alpha = 0.4f))) {
+                    val w = size.width
+                    val h = size.height
+                    val cx = w / 2f
+                    val cy = h / 2f
+                    val radius = (minOf(w, h) * 0.36f)
+                    val n = nodes.size
+                    if (n == 1) {
+                        // Single node centered
+                        drawCircle(color = Color(0xFF00C851), radius = 12f, center = androidx.compose.ui.geometry.Offset(cx, cy))
+                    } else {
+                        // Circular layout
+                        val positions = nodes.mapIndexed { i, node ->
+                            val angle = (2 * Math.PI * i.toDouble()) / n
+                            val x = cx + (radius * Math.cos(angle)).toFloat()
+                            val y = cy + (radius * Math.sin(angle)).toFloat()
+                            node.peerID to androidx.compose.ui.geometry.Offset(x, y)
+                        }.toMap()
+
+                        // Draw edges
+                        edges.forEach { e ->
+                            val p1 = positions[e.a]
+                            val p2 = positions[e.b]
+                            if (p1 != null && p2 != null) {
+                                if (e.isConfirmed) {
+                                    drawLine(color = Color(0xFF4A90E2), start = p1, end = p2, strokeWidth = 2f)
+                                } else {
+                                    // Unconfirmed: draw "solid" from declarer, "dashed" from other
+                                    val start = if (e.confirmedBy == e.a) p1 else p2
+                                    val end = if (e.confirmedBy == e.a) p2 else p1
+                                    
+                                    val midX = (start.x + end.x) / 2
+                                    val midY = (start.y + end.y) / 2
+                                    val mid = androidx.compose.ui.geometry.Offset(midX, midY)
+                                    
+                                    // Solid half
+                                    drawLine(color = Color(0xFF4A90E2), start = start, end = mid, strokeWidth = 2f)
+                                    
+                                    // Dotted half
+                                    drawLine(
+                                        color = Color(0xFF4A90E2),
+                                        start = mid,
+                                        end = end,
+                                        strokeWidth = 2f,
+                                        pathEffect = androidx.compose.ui.graphics.PathEffect.dashPathEffect(floatArrayOf(5f, 5f), 0f)
+                                    )
+                                }
+                            }
+                        }
+
+                        // Draw nodes
+                        nodes.forEach { node ->
+                            val pos = positions[node.peerID] ?: androidx.compose.ui.geometry.Offset(cx, cy)
+                            drawCircle(color = Color(0xFF00C851), radius = 10f, center = pos)
+                        }
+
+                        // Draw labels near nodes (nickname or short ID)
+                        val labelColor = colorScheme.onSurface.toArgb()
+                        val textSizePx = 10.sp.toPx()
+                        drawIntoCanvas { canvas ->
+                            val paint = android.graphics.Paint().apply {
+                                isAntiAlias = true
+                                color = labelColor
+                                textSize = textSizePx
+                            }
+                            nodes.forEach { node ->
+                                val pos = positions[node.peerID] ?: androidx.compose.ui.geometry.Offset(cx, cy)
+                                val label = (node.nickname?.takeIf { it.isNotBlank() } ?: node.peerID.take(8))
+                                canvas.nativeCanvas.drawText(label, pos.x + 12f, pos.y - 12f, paint)
+                            }
+                        }
+                    }
+                }
+                // Label list for clarity under the canvas
+                LazyColumn(modifier = Modifier.fillMaxWidth().heightIn(max = 140.dp)) {
+                    items(nodes.size) { i ->
+                        val node = nodes[i]
+                        val label = "${node.peerID.take(8)} • ${node.nickname ?: "unknown"}"
+                        Text(label, fontFamily = FontFamily.Monospace, fontSize = 11.sp, color = colorScheme.onSurface.copy(alpha = 0.85f))
+                    }
+                }
+            }
+        }
+    }
+}
+
 private enum class GraphMode { OVERALL, PER_DEVICE, PER_PEER }
 
 @OptIn(ExperimentalMaterial3Api::class, ExperimentalLayoutApi::class)
@@ -139,6 +247,11 @@ fun DebugSettingsSheet(
                 }
             }
 
+            // Mesh topology visualization (moved below verbose logging)
+            item {
+                MeshTopologySection()
+            }
+
             // GATT controls
             item {
                 Surface(shape = RoundedCornerShape(12.dp), color = colorScheme.surfaceVariant.copy(alpha = 0.2f)) {
@@ -488,9 +601,6 @@ fun DebugSettingsSheet(
                 }
             }
 
-
-
-
             // Connected devices
             item {
                 Surface(shape = RoundedCornerShape(12.dp), color = colorScheme.surfaceVariant.copy(alpha = 0.2f)) {

app/src/test/java/com/bitchat/android/mesh/FragmentManagerTest.kt

@@ -0,0 +1,191 @@
+package com.bitchat.android.mesh
+
+import com.bitchat.android.protocol.BitchatPacket
+import com.bitchat.android.protocol.MessageType
+import com.bitchat.android.model.FragmentPayload
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNotNull
+import org.junit.Assert.assertTrue
+import org.junit.Before
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.robolectric.RobolectricTestRunner
+import java.util.Random
+
+@RunWith(RobolectricTestRunner::class)
+class FragmentManagerTest {
+
+    private lateinit var fragmentManager: FragmentManager
+    private val senderID = "1122334455667788"
+    private val recipientID = "8877665544332211"
+
+    @Before
+    fun setup() {
+        fragmentManager = FragmentManager()
+    }
+
+    @Test
+    fun `test fragmentation without route`() {
+        // Create a large payload (e.g., 1000 bytes)
+        val payload = ByteArray(1000)
+        Random().nextBytes(payload)
+
+        val packet = BitchatPacket(
+            version = 1u,
+            type = MessageType.MESSAGE.value,
+            senderID = hexStringToByteArray(senderID),
+            recipientID = hexStringToByteArray(recipientID),
+            timestamp = System.currentTimeMillis().toULong(),
+            payload = payload,
+            ttl = 7u,
+            route = null
+        )
+
+        val fragments = fragmentManager.createFragments(packet)
+
+        assertTrue("Should create multiple fragments", fragments.size > 1)
+        
+        // Verify each fragment fits in MTU (512)
+        for (fragment in fragments) {
+            val encodedSize = fragment.toBinaryData()?.size ?: 0
+            assertTrue("Fragment encoded size should be <= 512, was $encodedSize", encodedSize <= 512)
+            
+            // Inspect the payload data size
+            val fragmentPayload = FragmentPayload.decode(fragment.payload)
+            assertNotNull(fragmentPayload)
+        }
+    }
+
+    @Test
+    fun `test fragmentation with route`() {
+        // Create a large payload
+        val payload = ByteArray(1000)
+        Random().nextBytes(payload)
+        
+        // Create a fake route (3 hops)
+        val route = listOf(
+            hexStringToByteArray("AABBCCDDEEFF0011"),
+            hexStringToByteArray("1100FFEEDDCCBBAA"),
+            hexStringToByteArray("1234567890ABCDEF")
+        )
+
+        val packet = BitchatPacket(
+            version = 2u,
+            type = MessageType.MESSAGE.value,
+            senderID = hexStringToByteArray(senderID),
+            recipientID = hexStringToByteArray(recipientID),
+            timestamp = System.currentTimeMillis().toULong(),
+            payload = payload,
+            ttl = 7u,
+            route = route
+        )
+
+        val fragments = fragmentManager.createFragments(packet)
+
+        assertTrue("Should create multiple fragments", fragments.size > 1)
+
+        // Verify fragments retain the route and version 2
+        for (fragment in fragments) {
+            assertEquals("Fragment version should be 2", 2u.toUByte(), fragment.version)
+            assertEquals("Fragment should have the route", route.size, fragment.route?.size)
+            
+            val encodedSize = fragment.toBinaryData()?.size ?: 0
+            assertTrue("Fragment encoded size should be <= 512, was $encodedSize", encodedSize <= 512)
+        }
+    }
+    
+    @Test
+    fun `test fragmentation size difference with and without route`() {
+        // This test specifically checks if the dynamic calculation logic works 
+        // by observing that fragments with routes carry less data payload per fragment
+        
+        val payload = ByteArray(2000) // Large enough to ensure full fragments
+        Random().nextBytes(payload)
+        
+        // 1. Without route
+        val packetNoRoute = BitchatPacket(
+            version = 1u,
+            type = MessageType.MESSAGE.value,
+            senderID = hexStringToByteArray(senderID),
+            recipientID = hexStringToByteArray(recipientID),
+            timestamp = System.currentTimeMillis().toULong(),
+            payload = payload,
+            ttl = 7u,
+            route = null
+        )
+        val fragmentsNoRoute = fragmentManager.createFragments(packetNoRoute)
+        val firstFragPayloadNoRoute = FragmentPayload.decode(fragmentsNoRoute[0].payload)
+        val dataSizeNoRoute = firstFragPayloadNoRoute?.data?.size ?: 0
+        
+        // 2. With large route (e.g., 5 hops)
+        val route = List(5) { hexStringToByteArray("000000000000000$it") }
+        val packetWithRoute = BitchatPacket(
+            version = 2u,
+            type = MessageType.MESSAGE.value,
+            senderID = hexStringToByteArray(senderID),
+            recipientID = hexStringToByteArray(recipientID),
+            timestamp = System.currentTimeMillis().toULong(),
+            payload = payload,
+            ttl = 7u,
+            route = route
+        )
+        val fragmentsWithRoute = fragmentManager.createFragments(packetWithRoute)
+        val firstFragPayloadWithRoute = FragmentPayload.decode(fragmentsWithRoute[0].payload)
+        val dataSizeWithRoute = firstFragPayloadWithRoute?.data?.size ?: 0
+        
+        println("Data size without route: $dataSizeNoRoute")
+        println("Data size with route: $dataSizeWithRoute")
+        
+        assertTrue("Data payload should be smaller with route", dataSizeWithRoute < dataSizeNoRoute)
+        
+        // Rough verification of the math:
+        // 5 hops * 8 bytes = 40 bytes extra.
+        // Plus v2 header overhead differences.
+        // The difference should be roughly 40+ bytes.
+        assertTrue("Difference should be significant", (dataSizeNoRoute - dataSizeWithRoute) >= 40)
+    }
+
+    @Test
+    fun `test reassembly`() {
+        val originalPayload = ByteArray(1500)
+        Random().nextBytes(originalPayload)
+        
+        val originalPacket = BitchatPacket(
+            version = 1u,
+            type = MessageType.FILE_TRANSFER.value,
+            senderID = hexStringToByteArray(senderID),
+            recipientID = hexStringToByteArray(recipientID),
+            timestamp = System.currentTimeMillis().toULong(),
+            payload = originalPayload,
+            ttl = 7u
+        )
+        
+        val fragments = fragmentManager.createFragments(originalPacket)
+        
+        var reassembledPacket: BitchatPacket? = null
+        
+        // Feed fragments back into FragmentManager
+        // Note: FragmentManager stores state in incomingFragments
+        
+        for (fragment in fragments) {
+            val result = fragmentManager.handleFragment(fragment)
+            if (result != null) {
+                reassembledPacket = result
+            }
+        }
+        
+        assertNotNull("Should have reassembled packet", reassembledPacket)
+        assertEquals("Type should match", originalPacket.type, reassembledPacket!!.type)
+        assertEquals("Payload size should match", originalPacket.payload.size, reassembledPacket.payload.size)
+        assertTrue("Payload content should match", originalPacket.payload.contentEquals(reassembledPacket.payload))
+    }
+
+    private fun hexStringToByteArray(hexString: String): ByteArray {
+        val result = ByteArray(8)
+        for (i in 0 until 8) {
+            val byteStr = hexString.substring(i * 2, i * 2 + 2)
+            result[i] = byteStr.toInt(16).toByte()
+        }
+        return result
+    }
+}

app/src/test/kotlin/com/bitchat/android/mesh/PacketRelayManagerTest.kt

@@ -0,0 +1,117 @@
+
+package com.bitchat.android.mesh
+
+import com.bitchat.android.model.RoutedPacket
+import com.bitchat.android.protocol.BitchatPacket
+import com.bitchat.android.protocol.MessageType
+import com.bitchat.android.util.toHexString
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.test.runTest
+import org.junit.Before
+import org.junit.Test
+import org.mockito.kotlin.any
+import org.mockito.kotlin.mock
+import org.mockito.kotlin.never
+import org.mockito.kotlin.verify
+import org.mockito.kotlin.whenever
+
+@ExperimentalCoroutinesApi
+class PacketRelayManagerTest {
+
+    private lateinit var packetRelayManager: PacketRelayManager
+    private val delegate: PacketRelayManagerDelegate = mock()
+
+    private val myPeerID = "1111111111111111"
+    private val otherPeerID = "2222222222222222"
+    private val nextHopPeerID = "3333333333333333"
+    private val finalRecipientID = "4444444444444444"
+
+    @Before
+    fun setUp() {
+        packetRelayManager = PacketRelayManager(myPeerID)
+        packetRelayManager.delegate = delegate
+        whenever(delegate.getNetworkSize()).thenReturn(10)
+        whenever(delegate.getBroadcastRecipient()).thenReturn(byteArrayOf(0,0,0,0,0,0,0,0))
+    }
+
+    private fun createPacket(route: List<ByteArray>?, recipient: String? = null): BitchatPacket {
+        return BitchatPacket(
+            type = MessageType.MESSAGE.value,
+            senderID = hexStringToPeerBytes(otherPeerID),
+            recipientID = recipient?.let { hexStringToPeerBytes(it) },
+            timestamp = System.currentTimeMillis().toULong(),
+            payload = "hello".toByteArray(),
+            ttl = 5u,
+            route = route
+        )
+    }
+
+    @Test
+    fun `packet with duplicate hops is dropped`() = runTest {
+        val route = listOf(
+            hexStringToPeerBytes(nextHopPeerID),
+            hexStringToPeerBytes(nextHopPeerID)
+        )
+        val packet = createPacket(route)
+        val routedPacket = RoutedPacket(packet, otherPeerID)
+
+        packetRelayManager.handlePacketRelay(routedPacket)
+
+        verify(delegate, never()).sendToPeer(any(), any())
+        verify(delegate, never()).broadcastPacket(any())
+    }
+
+    @Test
+    fun `valid source-routed packet is relayed to next hop`() = runTest {
+        val route = listOf(
+            hexStringToPeerBytes(myPeerID),
+            hexStringToPeerBytes(nextHopPeerID)
+        )
+        val packet = createPacket(route, finalRecipientID)
+        val routedPacket = RoutedPacket(packet, otherPeerID)
+        whenever(delegate.sendToPeer(any(), any())).thenReturn(true)
+
+        packetRelayManager.handlePacketRelay(routedPacket)
+
+        verify(delegate).sendToPeer(org.mockito.kotlin.eq(nextHopPeerID), any())
+        verify(delegate, never()).broadcastPacket(any())
+    }
+
+    @Test
+    fun `last hop does not relay further`() = runTest {
+        val route = listOf(
+            hexStringToPeerBytes(myPeerID)
+        )
+        val packet = createPacket(route, finalRecipientID)
+        val routedPacket = RoutedPacket(packet, otherPeerID)
+        whenever(delegate.sendToPeer(any(), any())).thenReturn(true)
+
+        packetRelayManager.handlePacketRelay(routedPacket)
+
+        verify(delegate).sendToPeer(org.mockito.kotlin.eq(finalRecipientID), any())
+        verify(delegate, never()).broadcastPacket(any())
+    }
+    
+    @Test
+    fun `packet with empty route is broadcast`() = runTest {
+        val packet = createPacket(null)
+        val routedPacket = RoutedPacket(packet, otherPeerID)
+
+        packetRelayManager.handlePacketRelay(routedPacket)
+
+        verify(delegate, never()).sendToPeer(any(), any())
+        verify(delegate).broadcastPacket(any())
+    }
+
+    private fun hexStringToPeerBytes(hex: String): ByteArray {
+        val result = ByteArray(8)
+        var idx = 0
+        var out = 0
+        while (idx + 1 < hex.length && out < 8) {
+            val b = hex.substring(idx, idx + 2).toIntOrNull(16)?.toByte() ?: 0
+            result[out++] = b
+            idx += 2
+        }
+        return result
+    }
+}

docs/SOURCE_ROUTING.md

@@ -1,78 +1,142 @@
-# Source-Based Routing for BitChat Packets
+# Source-Based Routing for BitChat Packets (v2)
 
-This document specifies an optional source-based routing extension to the BitChat packet format. A sender may attach a hop-by-hop route (list of peer IDs) to instruct relays on the intended path. Relays that support this feature will try to forward to the next hop directly; otherwise, they fall back to regular broadcast relaying.
+This document specifies the Source-Based Routing extension (v2) for the BitChat protocol. This upgrade enables efficient unicast routing across the mesh by allowing senders to specify an explicit path of intermediate relays.
 
-Status: optional and backward-compatible.
+**Status:** Implemented in Android and iOS. Backward compatible (v1 clients ignore routing data).
 
-## Layering Overview
+---
 
-- Outer packet: BitChat binary packet with unchanged fixed header (version/type/ttl/timestamp/flags/payloadLength).
+## 1. Protocol Versioning & Layering
-- Flags: adds a new bit `HAS_ROUTE (0x08)`.
-- Variable sections (when present, in order):
-  1) `SenderID` (8 bytes)
-  2) `RecipientID` (8 bytes) if `HAS_RECIPIENT`
-  3) `Route` (if `HAS_ROUTE`): `count` (1 byte) + `count * 8` bytes hop IDs
-  4) `Payload` (with optional compression preamble)
-  5) `Signature` (64 bytes) if `HAS_SIGNATURE`
 
-Unknown flags are ignored by older implementations (they will simply not see a route and continue broadcasting as before).
+To support source routing and larger payloads, the packet format has been upgraded to **Version 2**.
 
-## Route Field Encoding
+*   **Version 1 (Legacy):** 2-byte payload length limit. Ignores routing flags.
+*   **Version 2 (Current):** 4-byte payload length limit. Supports Source Routing.
 
-- Presence: Signaled by the `HAS_ROUTE (0x08)` bit in `flags`.
+**Key Rule:** The `HAS_ROUTE (0x08)` flag is **only valid** if the packet `version >= 2`. Relays receiving a v1 packet must ignore this flag even if set.
-- Layout (immediately after optional `RecipientID`):
-  - `count`: 1 byte (0..255)
-  - `hops`: concatenation of `count` peer IDs, each encoded as exactly 8 bytes
-- Peer ID encoding (8 bytes): same as used elsewhere in BitChat (16 hex chars → 8 bytes; left-to-right conversion; pad with `0x00` if shorter). This matches the on‑wire `senderID`/`recipientID` encoding.
-- Size impact: `1 + 8*N` bytes, where `N = count`.
-- Empty route: `HAS_ROUTE` with `count = 0` is treated as no route (relays ignore it).
 
-## Sender Behavior
+---
 
-- Applicability: Intended for addressed packets (i.e., where `recipientID` is set and is not the broadcast ID). For broadcast packets, omit the route.
+## 2. Packet Structure Comparison
-- Path computation: Use Dijkstra’s shortest path (unit weights) on your internal mesh topology to find a route from `src` (your peerID) to `dst` (recipient peerID). The hop list SHOULD include the full path `[src, ..., dst]`.
-- Encoding: Set `HAS_ROUTE`, write `count = path.length`, then the 8‑byte hop IDs in order. Keep `count <= 255`.
-- Signing: The route is covered by the Ed25519 signature (recommended):
-  - Signature input is the canonical encoding with `signature` omitted and `ttl = 0` (TTL excluded to allow relay decrement) — same rule as base protocol.
 
-## Relay Behavior
+The following diagram illustrates the structural differences between a standard v1 packet and a source-routed v2 packet.
 
-When receiving a packet that is not addressed to you:
+### V1 Packet (Legacy)
+```text
++-------------------+---------------------------------------------------------+
+| Fixed Header (14) | Variable Sections                                       |
++-------------------+----------+-------------+------------------+-------------+
+| Ver: 1 (1B)       | SenderID | RecipientID | Payload          | Signature   |
+| Type, TTL, etc.   | (8B)     | (8B)        | (Length in Head) | (64B)       |
+| Len: 2 Bytes      |          | (Optional)  |                  | (Optional)  |
++-------------------+----------+-------------+------------------+-------------+
+```
 
-1) If `HAS_ROUTE` is not set, or the route is empty, relay using your normal broadcast logic (subject to TTL/probability policies).
+### V2 Packet (Source Routed)
-2) If `HAS_ROUTE` is set and your peer ID appears at index `i` in the hop list:
+```text
-   - If there is a next hop at `i+1`, attempt a targeted unicast to that next hop if you have a direct connection to it.
++-------------------+-----------------------------------------------------------------------------+
-     - If successful, do NOT broadcast this packet further.
+| Fixed Header (16) | Variable Sections                                                           |
-     - If not directly connected (or the send fails), fall back to broadcast relaying.
++-------------------+----------+-------------+-----------------------+------------------+-------------+
-   - If you are the last hop (no `i+1`), proceed with standard handling (e.g., if not addressed to you, do not relay further).
+| Ver: 2 (1B)       | SenderID | RecipientID | SOURCE ROUTE          | Payload          | Signature   |
+| Type, TTL, etc.   | (8B)     | (8B)        | (Variable)            | (Length in Head) | (64B)       |
+| Len: 4 Bytes      |          | (Required*) | Only if HAS_ROUTE=1   |                  | (Optional)  |
++-------------------+----------+-------------+-----------------------+------------------+-------------+
+```
 
-TTL handling remains unchanged: relays decrement TTL by 1 before forwarding (whether targeted or broadcast). If TTL reaches 0, do not relay.
+**(*) Note:** A `Route` can be attached to **any** packet type that has a `RecipientID` (flag `HAS_RECIPIENT` set).
 
-## Receiver Behavior (Destination)
+### Fixed Header Differences
 
-- This extension does not change how addressed packets are handled by the final recipient. If the packet is addressed to you (`recipientID == myPeerID`), process it normally (e.g., decrypt Noise payload, verify signatures, etc.).
+| Field | Size (v1) | Size (v2) | Description |
-- Signature verification MUST include the route field when present; route tampering will invalidate the signature.
+|---|---|---|---|
+| **Version** | 1 byte | 1 byte | `0x01` vs `0x02` |
+| **Payload Length** | **2 bytes** | **4 bytes** | `UInt32` in v2 to support large files. **Excludes** route/IDs/sig. |
+| **Total Size** | **14 bytes** | **16 bytes** | V2 header is 2 bytes larger. |
 
-## Compatibility
+---
 
-- Omission: If `HAS_ROUTE` is omitted, legacy behavior applies. Relays that don’t implement this feature will ignore the route entirely, because they won’t set or check `HAS_ROUTE`.
+## 3. Source Route Specification
-- Partial support: If any relay on the path cannot directly reach the next hop, it will fall back to broadcast relaying; delivery is still probabilistic like the base protocol.
 
-## Minimal Example (conceptual)
+The `Source Route` field is a variable-length list of **intermediate hops** that the packet must traverse.
 
-- Header (fixed 13 bytes): unchanged.
+*   **Location:** Immediately follows `RecipientID`.
-- Variable sections (ordered):
+*   **Structure:**
-  - `SenderID(8)`
+    *   `Count` (1 byte): Number of intermediate hops (`N`).
-  - `RecipientID(8)` (if present)
+    *   `Hops` (`N * 8` bytes): Sequence of Peer IDs.
-  - `HAS_ROUTE` set → `count=3`, `hops = [H0 H1 H2]` where each `Hk` is 8 bytes
-  - Payload (optionally compressed)
-  - Signature (64)
 
-Where `H0` is the sender’s peer ID, `H2` is the recipient’s peer ID, and `H1` is an intermediate relay. The receiver verifies the signature over the packet encoding (with `ttl = 0` and `signature` omitted), which includes the `hops` when `HAS_ROUTE` is set.
+### Intermediate Hops Only
+The route list MUST contain **only** the intermediate relays between the sender and the recipient.
+*   **DO NOT** include the `SenderID` (it is already in the packet).
+*   **DO NOT** include the `RecipientID` (it is already in the packet).
 
-## Operational Notes
+**Example:**
+Topology: `Alice (Sender) -> Bob -> Charlie -> Dave (Recipient)`
+*   Packet `SenderID`: Alice
+*   Packet `RecipientID`: Dave
+*   Packet `Route`: `[Bob, Charlie]` (Count = 2)
 
-- Routing optimality depends on the freshness and completeness of the topology your implementation has learned (e.g., via gossip of direct neighbors). Recompute routes as needed.
+---
-- Route length should be kept small to reduce overhead and the probability of missing a direct link at some hop.
-- Implementations may introduce policy controls (e.g., disable source routing, cap max route length).
 
+## 4. Topology Discovery (Gossip)
+
+To calculate routes, nodes need a view of the network topology. This is achieved via a **Neighbor List** extension to the `IdentityAnnouncement` packet.
+
+*   **Mechanism:** `IdentityAnnouncement` packets contain a TLV (Type-Length-Value) payload.
+*   **New TLV Type:** `0x04` (Direct Neighbors).
+*   **Content:** A list of Peer IDs that the announcing node is directly connected to.
+
+**TLV Structure (Type 0x04):**
+```text
+[Type: 0x04] [Length: 1B] [Count: 1B] [NeighborID1 (8B)] [NeighborID2 (8B)] ...
+```
+Nodes receiving this TLV update their local mesh graph, linking the sender to the listed neighbors.
+
+### Edge Verification (Two-Way Handshake)
+
+To prevent spoofing and routing through stale connections, the Mesh Graph service implements a strict two-way handshake verification:
+
+*   **Unconfirmed Edge:** If Peer A announces Peer B, but Peer B does *not* announce Peer A, the connection is treated as **unconfirmed**. Unconfirmed edges are visualized as dotted lines in debug tools but are **excluded** from route calculations.
+*   **Confirmed Edge:** An edge is only valid for routing when **both** peers explicitly announce each other in their neighbor lists. This ensures that the connection is bidirectional and currently active from both perspectives.
+
+---
+
+## 5. Fragmentation & Source Routing
+
+When a large source-routed packet (e.g., File Transfer) exceeds the MTU and requires fragmentation:
+
+1.  **Version Inheritance:** All fragments MUST be marked as **Version 2**.
+2.  **Route Inheritance:** All fragments MUST contain the **exact same Route field** as the parent packet.
+
+**Why?** If fragments were sent as v1 packets or without routes, they would fall back to flooding, negating the bandwidth benefits of source routing for large data transfers.
+
+---
+
+## 6. Security & Signing
+
+Source routing is fully secured by the existing Ed25519 signature scheme.
+
+*   **Scope:** The signature covers the **entire packet structure** (Header + Sender + Recipient + Route + Payload).
+*   **Verification:** The receiver verifies the signature against the `SenderID`'s public key.
+*   **Integrity:** Any tampering with the route list by malicious relays will invalidate the signature, causing the packet to be dropped by the destination.
+
+**Signature Input Construction:**
+Serialize the packet exactly as transmitted, but temporarily set `TTL = 0` and remove the `Signature` bytes.
+
+---
+
+## 7. Relay Logic
+
+When a node receives a packet **not** addressed to itself:
+
+1.  **Check Route:**
+    *   Is `Version >= 2`?
+    *   Is `HAS_ROUTE` flag set?
+    *   Is the route list non-empty?
+2.  **If YES (Source Routed):**
+    *   Find local Peer ID in the route list at index `i`.
+    *   **Next Hop:** The peer at `i + 1`.
+    *   **Last Hop:** If `i` is the last index, the Next Hop is the `RecipientID`.
+    *   **Action:** Attempt to unicast (`sendToPeer`) to the Next Hop.
+    *   **Fallback:** If the Next Hop is unreachable, **fall back to broadcast/flood** to ensure delivery.
+3.  **If NO (Standard):**
+    *   Flood the packet to all connected neighbors (subject to TTL and probability rules).