fix: show sidebar update banner from background checks

Sources/AppDelegate.swift

@@ -2221,8 +2221,7 @@ final class AppDelegate: NSObject, NSApplicationDelegate, UNUserNotificationCent
             configureUserNotifications()
             installMenuBarVisibilityObserver()
             syncMenuBarExtraVisibility()
-            // Sparkle updater is started lazily on first manual check. This avoids any
-            // first-launch permission prompts and keeps cmux aligned with the update pill UI.
+            updateController.startUpdaterIfNeeded()
         }
         titlebarAccessoryController.start()
         windowDecorationsController.start()

Sources/ContentView.swift

@@ -7789,6 +7789,10 @@ struct VerticalTabsSidebar: View {
                         Spacer()
                             .frame(height: trafficLightPadding)
 
+                        SidebarUpdateBanner(updateViewModel: updateViewModel)
+                            .padding(.horizontal, 8)
+                            .padding(.top, 8)
+
                         LazyVStack(spacing: tabRowSpacing) {
                             ForEach(Array(tabManager.tabs.enumerated()), id: \.element.id) { index, tab in
                                 TabItemView(
@@ -8719,6 +8723,107 @@ private final class SidebarShortcutHintModifierMonitor: ObservableObject {
     }
 }
 
+private struct SidebarUpdateBanner: View {
+    @ObservedObject var updateViewModel: UpdateViewModel
+
+    private var bannerVersion: String? {
+        if let detectedUpdateVersion = updateViewModel.detectedUpdateVersion {
+            return detectedUpdateVersion
+        }
+        if case .updateAvailable(let update) = updateViewModel.effectiveState {
+            return UpdateViewModel.normalizedDetectedUpdateVersion(from: update.appcastItem.displayVersionString)
+        }
+        return nil
+    }
+
+    private var titleText: String {
+        guard let bannerVersion else {
+            return String(localized: "update.available.short", defaultValue: "Update Available")
+        }
+        return String(localized: "update.available.withVersion", defaultValue: "Update Available: \(bannerVersion)")
+    }
+
+    private var messageText: String {
+        if case .updateAvailable = updateViewModel.effectiveState {
+            let message = updateViewModel.description
+            if !message.isEmpty {
+                return message
+            }
+        }
+        return String(localized: "update.downloadAndInstall", defaultValue: "Download and install the latest version")
+    }
+
+    private var actionDisabled: Bool {
+        switch updateViewModel.effectiveState {
+        case .checking, .downloading, .extracting, .installing:
+            return true
+        default:
+            return false
+        }
+    }
+
+    var body: some View {
+        if bannerVersion != nil {
+            VStack(alignment: .leading, spacing: 10) {
+                HStack(alignment: .top, spacing: 10) {
+                    Image(systemName: "shippingbox.fill")
+                        .font(.system(size: 13, weight: .semibold))
+                        .foregroundStyle(cmuxAccentColor())
+                        .padding(.top, 1)
+
+                    VStack(alignment: .leading, spacing: 4) {
+                        Text(titleText)
+                            .font(.system(size: 12, weight: .semibold))
+                            .foregroundColor(.primary)
+                            .accessibilityIdentifier("SidebarUpdateBannerTitle")
+                        Text(messageText)
+                            .font(.system(size: 11))
+                            .foregroundColor(.secondary)
+                            .fixedSize(horizontal: false, vertical: true)
+                    }
+
+                    Spacer(minLength: 0)
+                }
+
+                HStack {
+                    Spacer(minLength: 0)
+                    Button(String(localized: "common.installAndRelaunch", defaultValue: "Install and Relaunch")) {
+                        installDetectedUpdate()
+                    }
+                    .buttonStyle(.borderedProminent)
+                    .controlSize(.small)
+                    .disabled(actionDisabled)
+                    .accessibilityIdentifier("SidebarUpdateBannerAction")
+                }
+            }
+            .padding(12)
+            .frame(maxWidth: .infinity, alignment: .leading)
+            .background(
+                RoundedRectangle(cornerRadius: 12, style: .continuous)
+                    .fill(cmuxAccentColor().opacity(0.12))
+            )
+            .overlay(
+                RoundedRectangle(cornerRadius: 12, style: .continuous)
+                    .stroke(cmuxAccentColor().opacity(0.28), lineWidth: 1)
+            )
+            .contentShape(RoundedRectangle(cornerRadius: 12, style: .continuous))
+            .accessibilityIdentifier("SidebarUpdateBanner")
+        }
+    }
+
+    private func installDetectedUpdate() {
+        if case .updateAvailable(let update) = updateViewModel.effectiveState {
+            update.reply(.install)
+            return
+        }
+        if updateViewModel.effectiveState.isInstallable {
+            updateViewModel.effectiveState.confirm()
+            return
+        }
+        AppDelegate.shared?.attemptUpdate(nil)
+    }
+}
+
 private struct SidebarFooter: View {
     @ObservedObject var updateViewModel: UpdateViewModel
     let onSendFeedback: () -> Void

Sources/Update/UpdateController.swift

@@ -27,10 +27,10 @@ class UpdateController {
     }
 
     init() {
-        // Default to manual update checks. This also prevents Sparkle from prompting at startup.
+        // cmux checks for updates in the background, but keeps automatic download and
+        // profile submission disabled so all install intent stays user-driven.
         let defaults = UserDefaults.standard
         defaults.register(defaults: [
-            "SUEnableAutomaticChecks": false,
             "SUSendProfileInfo": false,
             "SUAutomaticallyUpdate": false,
         ])
@@ -59,8 +59,8 @@ class UpdateController {
         guard !didStartUpdater else { return }
         ensureSparkleInstallationCache()
 #if DEBUG
-        // UI tests need to exercise Sparkle's permission request deterministically.
-        // Clearing these defaults causes Sparkle to re-request permission on next start.
+        // Keep the permission-related defaults resettable for UI tests even though the
+        // delegate now suppresses Sparkle's permission UI entirely.
         if ProcessInfo.processInfo.environment["CMUX_UI_TEST_RESET_SPARKLE_PERMISSION"] == "1" {
             let defaults = UserDefaults.standard
             defaults.removeObject(forKey: "SUEnableAutomaticChecks")
@@ -71,13 +71,9 @@ class UpdateController {
         }
 #endif
         do {
-            // cmux never enables automatic update checks; we rely on the in-app update pill.
-            // Sparkle reads these from defaults, but set them explicitly before starting.
-            let defaults = UserDefaults.standard
-            defaults.set(false, forKey: "SUEnableAutomaticChecks")
-            defaults.set(false, forKey: "SUSendProfileInfo")
-            defaults.set(false, forKey: "SUAutomaticallyUpdate")
-
+            updater.automaticallyChecksForUpdates = true
+            updater.automaticallyDownloadsUpdates = false
+            updater.sendsSystemProfile = false
             try updater.start()
             didStartUpdater = true
         } catch {
@@ -201,7 +197,7 @@ class UpdateController {
     /// Validate the check for updates menu item.
     func validateMenuItem(_ item: NSMenuItem) -> Bool {
         if item.action == #selector(checkForUpdates) {
-            // Always allow user-initiated checks; we start Sparkle lazily on first use.
+            // Always allow user-initiated checks; Sparkle can safely surface current progress.
             return true
         }
         return true

Sources/Update/UpdateDelegate.swift

@@ -13,6 +13,10 @@ enum UpdateFeedResolver {
 }
 
 extension UpdateDriver: SPUUpdaterDelegate {
+    func updaterShouldPromptForPermissionToCheck(forUpdates _: SPUUpdater) -> Bool {
+        false
+    }
+
     func feedURLString(for updater: SPUUpdater) -> String? {
 #if DEBUG
         let env = ProcessInfo.processInfo.environment
@@ -35,6 +39,7 @@ extension UpdateDriver: SPUUpdaterDelegate {
     /// Called when an update is scheduled to install silently,
     /// which occurs when automatic download is enabled.
     func updater(_ updater: SPUUpdater, willInstallUpdateOnQuit item: SUAppcastItem, immediateInstallationBlock immediateInstallHandler: @escaping () -> Void) -> Bool {
+        viewModel.clearDetectedUpdate()
         viewModel.state = .installing(.init(
             isAutoUpdate: true,
             retryTerminatingApplication: immediateInstallHandler,
@@ -56,6 +61,7 @@ extension UpdateDriver: SPUUpdaterDelegate {
     }
 
     func updater(_ updater: SPUUpdater, didFindValidUpdate item: SUAppcastItem) {
+        viewModel.recordDetectedUpdate(item)
         let version = item.displayVersionString
         let fileURL = item.fileURL?.absoluteString ?? ""
         if fileURL.isEmpty {
@@ -66,6 +72,7 @@ extension UpdateDriver: SPUUpdaterDelegate {
     }
 
     func updaterDidNotFindUpdate(_ updater: SPUUpdater, error: Error) {
+        viewModel.clearDetectedUpdate()
         let nsError = error as NSError
         let reasonValue = (nsError.userInfo[SPUNoUpdateFoundReasonKey] as? NSNumber)?.intValue
         let reason = reasonValue.map { SPUNoUpdateFoundReason(rawValue: OSStatus($0)) } ?? nil
@@ -80,13 +87,18 @@ extension UpdateDriver: SPUUpdaterDelegate {
         }
     }
 
-    @MainActor
+    func updater(_ updater: SPUUpdater, userDidMake _: SPUUserUpdateChoice, forUpdate _: SUAppcastItem, state _: SPUUserUpdateState) {
+        viewModel.clearDetectedUpdate()
+    }
+
     func updaterWillRelaunchApplication(_ updater: SPUUpdater) {
-        AppDelegate.shared?.persistSessionForUpdateRelaunch()
-        TerminalController.shared.stop()
-        NSApp.invalidateRestorableState()
-        for window in NSApp.windows {
-            window.invalidateRestorableState()
+        Task { @MainActor in
+            AppDelegate.shared?.persistSessionForUpdateRelaunch()
+            TerminalController.shared.stop()
+            NSApp.invalidateRestorableState()
+            for window in NSApp.windows {
+                window.invalidateRestorableState()
+            }
         }
     }
 }

Sources/Update/UpdateTestSupport.swift

@@ -6,6 +6,14 @@ enum UpdateTestSupport {
     static func applyIfNeeded(to viewModel: UpdateViewModel) {
         let env = ProcessInfo.processInfo.environment
         guard env["CMUX_UI_TEST_MODE"] == "1" else { return }
+
+        if let detectedVersion = env["CMUX_UI_TEST_DETECTED_UPDATE_VERSION"],
+           !detectedVersion.isEmpty {
+            DispatchQueue.main.async {
+                viewModel.detectedUpdateVersion = UpdateViewModel.normalizedDetectedUpdateVersion(from: detectedVersion)
+            }
+        }
+
         guard let state = env["CMUX_UI_TEST_UPDATE_STATE"] else { return }
 
         DispatchQueue.main.async {

Sources/Update/UpdateViewModel.swift

@@ -6,6 +6,7 @@ import Sparkle
 class UpdateViewModel: ObservableObject {
     @Published var state: UpdateState = .idle
     @Published var overrideState: UpdateState?
+    @Published var detectedUpdateVersion: String?
     #if DEBUG
     @Published var debugOverrideText: String?
     #endif
@@ -14,6 +15,14 @@ class UpdateViewModel: ObservableObject {
         overrideState ?? state
     }
 
+    func recordDetectedUpdate(_ item: SUAppcastItem) {
+        detectedUpdateVersion = Self.normalizedDetectedUpdateVersion(from: item.displayVersionString)
+    }
+
+    func clearDetectedUpdate() {
+        detectedUpdateVersion = nil
+    }
+
     var text: String {
         #if DEBUG
         if let debugOverrideText { return debugOverrideText }
@@ -334,6 +343,11 @@ class UpdateViewModel: ObservableObject {
             return nil
         }
     }
+
+    static func normalizedDetectedUpdateVersion(from version: String) -> String? {
+        let trimmed = version.trimmingCharacters(in: .whitespacesAndNewlines)
+        return trimmed.isEmpty ? nil : trimmed
+    }
 }
 
 enum UpdateState: Equatable {

cmuxUITests/UpdatePillUITests.swift

@@ -124,6 +124,19 @@ final class UpdatePillUITests: XCTestCase {
         assertVisibleSize(noUpdatePill)
     }
 
+    func testSidebarUpdateBannerShowsForBackgroundDetectedUpdate() {
+        let systemSettings = XCUIApplication(bundleIdentifier: "com.apple.systempreferences")
+        systemSettings.terminate()
+        let app = XCUIApplication()
+        app.launchEnvironment["CMUX_UI_TEST_MODE"] = "1"
+        app.launchEnvironment["CMUX_UI_TEST_DETECTED_UPDATE_VERSION"] = "9.9.9"
+        launchAndActivate(app)
+
+        XCTAssertTrue(app.otherElements["SidebarUpdateBanner"].waitForExistence(timeout: 6.0))
+        XCTAssertTrue(app.staticTexts["Update Available: 9.9.9"].waitForExistence(timeout: 2.0))
+        XCTAssertTrue(app.buttons["SidebarUpdateBannerAction"].waitForExistence(timeout: 2.0))
+    }
+
     func testNoSparklePermissionDialogIsShown() {
         let systemSettings = XCUIApplication(bundleIdentifier: "com.apple.systempreferences")
         systemSettings.terminate()