feat: restore composer drafts across channel and DM switches

Save on leave and background, reload on enter, clear after send, and
wipe drafts during panic clear.

bitchat/ViewModels/ChatViewModel.swift

@@ -1637,6 +1637,7 @@ final class ChatViewModel: ObservableObject, BitchatDelegate, SynchronousMessage
         MeshSightingsTracker.shared.clear()
         MeshEchoSettings.reset()
         NotificationPrivacySettings.reset()
+        ComposerDraftStore.reset()
         // A hand-added relay names an operator someone chose to route through,
         // which is the kind of trace a wipe should not leave behind.
         NostrRelaySettings.reset()

bitchat/Views/ContentView.swift

@@ -98,6 +98,9 @@ struct ContentView: View {
 
     @StateObject private var voiceRecordingVM = VoiceRecordingViewModel()
     @State private var messageText = ""
+    /// Conversation the current `messageText` belongs to, so a channel switch
+    /// can save under the previous key before loading the next draft.
+    @State private var activeDraftKey: ComposerDraftStore.Key = .mesh
     @FocusState private var isTextFieldFocused: Bool
     @Environment(\.colorScheme) var colorScheme
     @Environment(\.appTheme) private var appTheme
@@ -241,6 +244,11 @@ struct ContentView: View {
                 }
                 #endif
                 sharedContentImportModel.updateDestination(sharedContentDestination)
+                activeDraftKey = ComposerDraftStore.Key.from(
+                    peerID: selectedPrivatePeerID,
+                    channel: locationChannelsModel.selectedChannel
+                )
+                messageText = ComposerDraftStore.load(activeDraftKey)
             }
             .onChange(of: colorScheme) { newValue in
                 conversationUIModel.setCurrentColorScheme(newValue)
@@ -258,9 +266,26 @@ struct ContentView: View {
                 showSidebar = true
             }
             sharedContentImportModel.updateDestination(sharedContentDestination)
+            switchComposerDraft(to: ComposerDraftStore.Key.from(
+                peerID: newValue,
+                channel: locationChannelsModel.selectedChannel
+            ))
         }
-        .onChange(of: locationChannelsModel.selectedChannel) { _ in
+        .onChange(of: locationChannelsModel.selectedChannel) { newChannel in
             sharedContentImportModel.updateDestination(sharedContentDestination)
+            // Private drafts are keyed by peer; only public channel switches
+            // need a draft swap while no DM is open.
+            if selectedPrivatePeerID == nil {
+                switchComposerDraft(to: ComposerDraftStore.Key.from(
+                    peerID: nil,
+                    channel: newChannel
+                ))
+            }
+        }
+        .onChange(of: scenePhase) { phase in
+            if phase == .background || phase == .inactive {
+                ComposerDraftStore.save(messageText, for: activeDraftKey)
+            }
         }
         .sheet(
             isPresented: Binding(
@@ -541,9 +566,17 @@ struct ContentView: View {
         guard let trimmed = messageText.trimmedOrNilIfEmpty else { return }
 
         messageText = ""
+        ComposerDraftStore.save("", for: activeDraftKey)
 
         DispatchQueue.main.async {
             self.conversationUIModel.sendMessage(trimmed)
         }
     }
+
+    private func switchComposerDraft(to newKey: ComposerDraftStore.Key) {
+        guard newKey != activeDraftKey else { return }
+        ComposerDraftStore.save(messageText, for: activeDraftKey)
+        activeDraftKey = newKey
+        messageText = ComposerDraftStore.load(newKey)
+    }
 }