Keep update popover primary buttons legible when the popover is not key

Packages/macOS/CmuxUpdaterUI/Sources/CmuxUpdaterUI/UpdateErrorView.swift

@@ -51,7 +51,7 @@ struct UpdateErrorView: View {
                     }
                     .frame(maxWidth: .infinity)
                 }
-                .buttonStyle(.borderedProminent)
+                .updatePrimaryButtonStyle()
                 .controlSize(.small)
             }
 

Packages/macOS/CmuxUpdaterUI/Sources/CmuxUpdaterUI/UpdatePopoverView.swift

@@ -169,7 +169,7 @@ private struct DetectedBackgroundUpdateView: View {
                         dismiss()
                     }
                     .keyboardShortcut(.defaultAction)
-                    .buttonStyle(.borderedProminent)
+                    .updatePrimaryButtonStyle()
                     .controlSize(.small)
                 }
             }
@@ -248,7 +248,7 @@ private struct PermissionRequestView: View {
                     dismiss()
                 }
                 .keyboardShortcut(.defaultAction)
-                .buttonStyle(.borderedProminent)
+                .updatePrimaryButtonStyle()
             }
         }
         .padding(16)
@@ -323,7 +323,7 @@ private struct UpdateAvailableView: View {
                         dismiss()
                     }
                     .keyboardShortcut(.defaultAction)
-                    .buttonStyle(.borderedProminent)
+                    .updatePrimaryButtonStyle()
                     .controlSize(.small)
                 }
             }
@@ -425,7 +425,7 @@ private struct InstallingView: View {
                     dismiss()
                 }
                 .keyboardShortcut(.defaultAction)
-                .buttonStyle(.borderedProminent)
+                .updatePrimaryButtonStyle()
                 .controlSize(.small)
             }
         }

Packages/macOS/CmuxUpdaterUI/Sources/CmuxUpdaterUI/View+UpdatePrimaryButton.swift

@@ -0,0 +1,14 @@
+import SwiftUI
+
+extension View {
+    /// `.borderedProminent` that keeps its accent bezel and label when the popover's window is not key.
+    ///
+    /// The update popover usually opens without becoming the key window, so SwiftUI reports an
+    /// inactive control state. AppKit then draws the inactive gray bezel under the prominent
+    /// label and the primary action ("Install and Relaunch") shows as an empty gray box (#18687).
+    /// Same treatment as the Cloud enablement buttons (`cloudProminentButtonStyle`).
+    func updatePrimaryButtonStyle() -> some View {
+        buttonStyle(.borderedProminent)
+            .environment(\.controlActiveState, .key)
+    }
+}

Packages/macOS/CmuxUpdaterUI/Tests/CmuxUpdaterUITests/UpdatePrimaryButtonStyleTests.swift

@@ -0,0 +1,74 @@
+import AppKit
+import SwiftUI
+import Testing
+@testable import CmuxUpdaterUI
+
+@MainActor
+@Suite("Update primary button style", .serialized)
+struct UpdatePrimaryButtonStyleTests {
+    @Test("Primary update actions draw as key while the popover window is inactive (#18687)")
+    func primaryButtonIgnoresInactiveWindowState() {
+        let recorder = ControlActiveStateRecorder()
+        let window = host(
+            ControlActiveStateProbe(recorder: recorder)
+                .updatePrimaryButtonStyle()
+                .environment(\.controlActiveState, .inactive)
+        )
+        defer { window.orderOut(nil) }
+        pump { !recorder.states.isEmpty }
+
+        #expect(!recorder.states.isEmpty, "the probe must render")
+        #expect(recorder.states.allSatisfy { $0 == .key })
+    }
+
+    @Test("The probe sees the inactive state without the primary style")
+    func probeObservesInactiveStateWithoutPrimaryStyle() {
+        let recorder = ControlActiveStateRecorder()
+        let window = host(
+            ControlActiveStateProbe(recorder: recorder)
+                .environment(\.controlActiveState, .inactive)
+        )
+        defer { window.orderOut(nil) }
+        pump { !recorder.states.isEmpty }
+
+        #expect(recorder.states.last == .inactive)
+    }
+
+    private func host(_ view: some View) -> NSWindow {
+        let hosting = NSHostingView(rootView: view)
+        hosting.frame = NSRect(x: 0, y: 0, width: 120, height: 40)
+        let window = NSWindow(
+            contentRect: NSRect(x: -4000, y: -4000, width: 120, height: 40),
+            styleMask: [.borderless],
+            backing: .buffered,
+            defer: false
+        )
+        window.contentView = hosting
+        window.orderBack(nil)
+        hosting.layoutSubtreeIfNeeded()
+        return window
+    }
+
+    /// Pumps the main run loop until `condition` or a bounded deadline (test scaffolding only).
+    private func pump(until condition: () -> Bool) {
+        let deadline = ContinuousClock.now.advanced(by: .seconds(3))
+        while !condition(), ContinuousClock.now < deadline {
+            RunLoop.main.run(until: Date().addingTimeInterval(0.02))
+        }
+    }
+}
+
+@MainActor
+private final class ControlActiveStateRecorder {
+    var states: [ControlActiveState] = []
+}
+
+private struct ControlActiveStateProbe: View {
+    let recorder: ControlActiveStateRecorder
+    @Environment(\.controlActiveState) private var controlActiveState
+
+    var body: some View {
+        recorder.states.append(controlActiveState)
+        return Color.clear.frame(width: 10, height: 10)
+    }
+}