add IDLE monitoring to SyncCoordinator: start/stop with capability check

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

Packages/MagnumOpusCore/Sources/SyncEngine/SyncCoordinator.swift

@@ -13,7 +13,10 @@ public final class SyncCoordinator {
 	private let store: MailStore
 	private let actionQueue: ActionQueue?
 	private let taskStore: TaskStore?
+	private let credentials: Credentials?
 	private var syncTask: Task<Void, Never>?
+	private var idleClient: IMAPIdleClient?
+	private var idleActive = false
 
 	public private(set) var syncState: SyncState = .idle
 	private var eventHandlers: [(SyncEvent) -> Void] = []
@@ -23,13 +26,15 @@ public final class SyncCoordinator {
 		imapClient: any IMAPClientProtocol,
 		store: MailStore,
 		actionQueue: ActionQueue? = nil,
-		taskStore: TaskStore? = nil
+		taskStore: TaskStore? = nil,
+		credentials: Credentials? = nil
 	) {
 		self.accountConfig = accountConfig
 		self.imapClient = imapClient
 		self.store = store
 		self.actionQueue = actionQueue
 		self.taskStore = taskStore
+		self.credentials = credentials
 	}
 
 	public func onEvent(_ handler: @escaping (SyncEvent) -> Void) {
@@ -286,6 +291,49 @@ public final class SyncCoordinator {
 		}
 	}
 
+	// MARK: - IMAP IDLE
+
+	/// Check server capabilities and start IDLE monitoring if supported.
+	/// Must be called after at least one successful sync (so capabilities are cached).
+	public func startIdleMonitoring() async {
+		guard let credentials else {
+			print("[SyncCoordinator] No credentials provided, cannot start IDLE")
+			return
+		}
+
+		do {
+			let caps = try await imapClient.capabilities()
+			guard caps.contains("IDLE") else {
+				print("[SyncCoordinator] Server does not support IDLE, using periodic sync only")
+				return
+			}
+
+			let client = IMAPIdleClient(
+				host: accountConfig.imapHost,
+				port: accountConfig.imapPort,
+				credentials: credentials
+			)
+
+			idleClient = client
+			idleActive = true
+
+			try await client.startMonitoring { [weak self] in
+				Task { @MainActor [weak self] in
+					try? await self?.syncNow()
+				}
+			}
+		} catch {
+			print("[SyncCoordinator] Failed to start IDLE monitoring: \(error)")
+		}
+	}
+
+	/// Stop IDLE monitoring and clean up.
+	public func stopIdleMonitoring() async {
+		idleActive = false
+		await idleClient?.stopMonitoring()
+		idleClient = nil
+	}
+
 	// MARK: - Periodic Sync
 
 	public func startPeriodicSync(interval: Duration = .seconds(300)) {