fix double sync race: remove duplicate syncNow calls, add sync guard

- connectAccount() and loadExistingAccount() no longer call syncNow() —
  the .task modifier on mailView handles initial sync + periodic sync
- add isSyncing guard to prevent concurrent syncNow() calls that race
  on the IMAP connection and cause "Previous command interrupted"
- reload mailboxes after each sync (needed on first sync when DB is empty)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Apps/MagnumOpus/ContentView.swift

@@ -165,11 +165,10 @@ struct ContentView: View {
 			try viewModel.setup(config: config, credentials: credentials)
 			try KeychainService.saveCredentials(credentials, for: config.id)
 			Self.saveAccountConfig(config)
+			// syncNow + startPeriodicSync happen via .task on mailView — don't duplicate
 			Task {
-				await viewModel.syncNow()
 				await viewModel.loadMailboxes(accountId: config.id)
 				viewModel.startObservingThreads(accountId: config.id)
-				viewModel.startPeriodicSync()
 			}
 		} catch {
 			accountSetup.errorMessage = error.localizedDescription
@@ -182,11 +181,10 @@ struct ContentView: View {
 		else { return }
 		do {
 			try viewModel.setup(config: config, credentials: credentials)
+			// syncNow + startPeriodicSync happen via .task on mailView — don't duplicate
 			Task {
 				await viewModel.loadMailboxes(accountId: config.id)
 				viewModel.startObservingThreads(accountId: config.id)
-				await viewModel.syncNow()
-				viewModel.startPeriodicSync()
 			}
 		} catch {
 			// Account config exists but setup failed — show account setup

Apps/MagnumOpus/ViewModels/MailViewModel.swift

@@ -201,11 +201,19 @@ final class MailViewModel {
 		}
 	}
 
+	private var isSyncing = false
+
 	func syncNow() async {
-		guard let coordinator else { return }
+		guard let coordinator, !isSyncing else { return }
+		isSyncing = true
+		defer { isSyncing = false }
 		do {
 			try await coordinator.syncNow()
 			syncState = coordinator.syncState
+			// Reload mailboxes after sync (they may have been created on first sync)
+			if let accountConfig {
+				await loadMailboxes(accountId: accountConfig.id)
+			}
 		} catch {
 			let desc = "\(error)"
 			print("[MailViewModel] syncNow failed: \(desc)")