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/ChatMediaTransferCoordinator.swift

@@ -34,11 +34,11 @@ final class ChatMediaTransferCoordinator {
         let transferId = makeTransferID(messageID: messageID)
 
         Task.detached(priority: .userInitiated) { [weak self] in
-            guard let self else { return }
             do {
                 let packet = try ChatMediaPreparation.prepareVoiceNotePacket(at: url)
 
-                await MainActor.run {
+                await MainActor.run { [weak self] in
+                    guard let self else { return }
                     self.registerTransfer(transferId: transferId, messageID: messageID)
                     if let peerID = targetPeer {
                         self.viewModel.meshService.sendFilePrivate(packet, to: peerID, transferId: transferId)
@@ -49,12 +49,14 @@ final class ChatMediaTransferCoordinator {
             } catch ChatMediaPreparationError.voiceNoteTooLarge(let size) {
                 SecureLogger.warning("Voice note exceeds size limit (\(size) bytes)", category: .session)
                 try? FileManager.default.removeItem(at: url)
-                await MainActor.run {
+                await MainActor.run { [weak self] in
+                    guard let self else { return }
                     self.handleMediaSendFailure(messageID: messageID, reason: "Voice note too large")
                 }
             } catch {
                 SecureLogger.error("Voice note send failed: \(error)", category: .session)
-                await MainActor.run {
+                await MainActor.run { [weak self] in
+                    guard let self else { return }
                     self.handleMediaSendFailure(messageID: messageID, reason: "Failed to send voice note")
                 }
             }
@@ -65,10 +67,10 @@ final class ChatMediaTransferCoordinator {
     func processThenSendImage(_ image: UIImage?) {
         guard let image else { return }
         Task.detached { [weak self] in
-            guard let self else { return }
             do {
                 let processedURL = try ImageUtils.processImage(image)
-                await MainActor.run {
+                await MainActor.run { [weak self] in
+                    guard let self else { return }
                     self.sendImage(from: processedURL)
                 }
             } catch {
@@ -80,10 +82,10 @@ final class ChatMediaTransferCoordinator {
     func processThenSendImage(from url: URL?) {
         guard let url else { return }
         Task.detached { [weak self] in
-            guard let self else { return }
             do {
                 let processedURL = try ImageUtils.processImage(at: url)
-                await MainActor.run {
+                await MainActor.run { [weak self] in
+                    guard let self else { return }
                     self.sendImage(from: processedURL)
                 }
             } catch {
@@ -112,11 +114,11 @@ final class ChatMediaTransferCoordinator {
         }
 
         Task.detached(priority: .userInitiated) { [weak self] in
-            guard let self else { return }
             do {
                 let prepared = try ChatMediaPreparation.prepareImagePacket(from: sourceURL)
 
-                await MainActor.run {
+                await MainActor.run { [weak self] in
+                    guard let self else { return }
                     let message = self.enqueueMediaMessage(
                         content: "\(MimeType.Category.image.messagePrefix)\(prepared.outputURL.lastPathComponent)",
                         targetPeer: targetPeer
@@ -132,12 +134,14 @@ final class ChatMediaTransferCoordinator {
                 }
             } catch ChatMediaPreparationError.imageTooLarge(let size) {
                 SecureLogger.warning("Processed image exceeds size limit (\(size) bytes)", category: .session)
-                await MainActor.run {
+                await MainActor.run { [weak self] in
+                    guard let self else { return }
                     self.viewModel.addSystemMessage("Image is too large to send.")
                 }
             } catch {
                 SecureLogger.error("Image send preparation failed: \(error)", category: .session)
-                await MainActor.run {
+                await MainActor.run { [weak self] in
+                    guard let self else { return }
                     self.viewModel.addSystemMessage("Failed to prepare image for sending.")
                 }
             }