Extract BLE packet handlers and migrate coordinators to narrow contexts

BLEService's per-packet-type orchestration moves into owned, tested
components (BLEAnnounceHandler, BLEPublicMessageHandler,
BLENoisePacketHandler, BLEFileTransferHandler, BLEFragmentHandler),
each taking an environment struct of closures so every queue hop stays
in BLEService and the handlers are synchronously testable. Behavior is
preserved verbatim, including Noise session recovery on decrypt failure
and single-block UI event ordering. handleLeave/handleRequestSync stay
in place as already-thin delegations. BLEService drops to 3393 lines.

Four coordinators (delivery, private conversation, Nostr, public
conversation) drop their unowned/weak ChatViewModel back-references for
narrow @MainActor context protocols, with ChatViewModel conformances as
single shared witnesses for overlapping members. Their true coupling is
now an explicit, reviewable surface, and each gains a mock-context test
suite covering flows previously testable only through the full view
model. Delivery/read acks now also clear the router's retained-send
outbox via the delivery context.

New LargeTopologyTests exercise production-shaped meshes with the
in-memory harness: an 8-peer relay chain with per-hop TTL decay, a
14-peer cyclic mesh with exactly-once delivery, partition/heal, and
topology churn.

App-layer runtime/model files updated alongside.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

bitchat/ViewModels/ChatViewModel.swift

@@ -152,11 +152,11 @@ final class ChatViewModel: ObservableObject, BitchatDelegate, TransportEventDele
     private lazy var peerListCoordinator = ChatPeerListCoordinator(viewModel: self)
     private lazy var messageFormatter = ChatMessageFormatter(viewModel: self)
     lazy var peerIdentityCoordinator = ChatPeerIdentityCoordinator(viewModel: self)
-    lazy var deliveryCoordinator = ChatDeliveryCoordinator(viewModel: self)
+    lazy var deliveryCoordinator = ChatDeliveryCoordinator(context: self)
     lazy var composerCoordinator = ChatComposerCoordinator(viewModel: self)
-    lazy var publicConversationCoordinator = ChatPublicConversationCoordinator(viewModel: self)
-    lazy var privateConversationCoordinator = ChatPrivateConversationCoordinator(viewModel: self)
-    lazy var nostrCoordinator = ChatNostrCoordinator(viewModel: self)
+    lazy var publicConversationCoordinator = ChatPublicConversationCoordinator(context: self)
+    lazy var privateConversationCoordinator = ChatPrivateConversationCoordinator(context: self)
+    lazy var nostrCoordinator = ChatNostrCoordinator(context: self)
     lazy var mediaTransferCoordinator = ChatMediaTransferCoordinator(viewModel: self)
     lazy var verificationCoordinator = ChatVerificationCoordinator(viewModel: self)
 
@@ -168,7 +168,7 @@ final class ChatViewModel: ObservableObject, BitchatDelegate, TransportEventDele
         get { privateChatManager.privateChats }
         set {
             privateChatManager.privateChats = newValue
-            synchronizePrivateConversationStore()
+            schedulePrivateConversationStoreSynchronization()
         }
     }
     var selectedPrivateChatPeer: PeerID? {
@@ -187,7 +187,7 @@ final class ChatViewModel: ObservableObject, BitchatDelegate, TransportEventDele
         get { privateChatManager.unreadMessages }
         set {
             privateChatManager.unreadMessages = newValue
-            synchronizePrivateConversationStore()
+            schedulePrivateConversationStoreSynchronization()
         }
     }
 
@@ -372,6 +372,7 @@ final class ChatViewModel: ObservableObject, BitchatDelegate, TransportEventDele
     // MARK: - Message Delivery Tracking
 
     var cancellables = Set<AnyCancellable>()
+    private var pendingPrivateConversationStoreSyncTask: Task<Void, Never>?
 
     var transferIdToMessageIDs: [String: [String]] {
         mediaTransferCoordinator.transferIdToMessageIDs
@@ -967,6 +968,17 @@ final class ChatViewModel: ObservableObject, BitchatDelegate, TransportEventDele
         publicConversationCoordinator.synchronizeAllPublicConversationStores()
     }
 
+    @MainActor
+    func schedulePrivateConversationStoreSynchronization() {
+        guard pendingPrivateConversationStoreSyncTask == nil else { return }
+        pendingPrivateConversationStoreSyncTask = Task { @MainActor [weak self] in
+            await Task.yield()
+            guard let self else { return }
+            self.pendingPrivateConversationStoreSyncTask = nil
+            self.synchronizePrivateConversationStore()
+        }
+    }
+
     @MainActor
     func synchronizePrivateConversationStore() {
         conversationStore.synchronizePrivateChats(