Refactor code structure for improved readability and maintainability

SocialIO/Sources/App/AppViewModel.swift

@@ -13,6 +13,7 @@ final class AppViewModel {
     var composeDraft = ComposeDraft()
     var threads: [MailThread] = []
     var isLoading = false
+    var isSending = false
     var errorMessage: String?
     var mailboxNavigationToken = UUID()
     var threadNavigationToken = UUID()
@@ -158,6 +159,7 @@ final class AppViewModel {
     func beginBackendControl() async {
         guard !isListeningForBackendCommands else { return }
         isListeningForBackendCommands = true
+        defer { isListeningForBackendCommands = false }
 
         for await command in controlService.commands() {
             apply(command: command)
@@ -206,17 +208,23 @@ final class AppViewModel {
         }
     }
 
-    func sendCurrentDraft() async {
+    func sendCurrentDraft() async -> Bool {
+        guard !isSending else { return false }
+
         let draft = composeDraft
-        isComposing = false
+        isSending = true
+        defer { isSending = false }
 
         do {
             let sentThread = try await service.send(draft: draft)
             threads.insert(sentThread, at: 0)
             selectedMailbox = .sent
             openThread(withID: sentThread.id)
+            isComposing = false
+            return true
         } catch {
             errorMessage = "Unable to send message."
+            return false
         }
     }