diff --git a/CHANGELOG.md b/CHANGELOG.md
index ca213521b7..9fdd062e85 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,7 @@
 ## 0.51.1 — Unreleased
 
 ### Fixed
+- Mission Control: stop the lifecycle keepalive window from participating as a floating all-Spaces window on macOS 27 (#2955). Thanks @phuchong89 for the diagnostics!
 - Cost history chart: localize the Projects, Conversations, session, and standard/fast mode labels that previously stayed English for all 23 app languages (#2983). Thanks @Yuxin-Qiao!
 ### Added
 - Usage & Spend: aggregate per-project spend into ranked, window-scoped rows and carry project/session breakdowns through the cached Codex prefill so the dashboard and the menu chart agree on project data (#2984). Thanks @Yuxin-Qiao!
diff --git a/Sources/CodexBar/HiddenWindowView.swift b/Sources/CodexBar/HiddenWindowView.swift
index 489e17e2e8..ec48e24f25 100644
--- a/Sources/CodexBar/HiddenWindowView.swift
+++ b/Sources/CodexBar/HiddenWindowView.swift
@@ -105,11 +105,11 @@ final class KeepaliveWindowConfiguratorView: NSView {
         guard let window = self.windowProvider(self) else { return }
 
         window.identifier = NSUserInterfaceItemIdentifier("CodexBarLifecycleKeepalive")
-        // Make the keepalive window truly invisible and non-interactive.
+        // Keep the live SwiftUI scene inert without projecting it across Spaces.
         window.styleMask = [.borderless]
-        window.collectionBehavior = [.auxiliary, .ignoresCycle, .transient, .canJoinAllSpaces]
+        window.collectionBehavior = [.auxiliary, .ignoresCycle, .transient]
         window.isExcludedFromWindowsMenu = true
-        window.level = .floating
+        window.level = .normal
         window.isOpaque = false
         window.alphaValue = 0
         window.backgroundColor = .clear
diff --git a/Tests/CodexBarTests/SettingsWindowOpeningTests.swift b/Tests/CodexBarTests/SettingsWindowOpeningTests.swift
index 2e937c91cf..e895624316 100644
--- a/Tests/CodexBarTests/SettingsWindowOpeningTests.swift
+++ b/Tests/CodexBarTests/SettingsWindowOpeningTests.swift
@@ -5,7 +5,7 @@ import Testing
 @MainActor
 struct SettingsWindowOpeningTests {
     @Test
-    func `recreated keepalive shell is configured and missing relay invokes settings fallback`() {
+    func `keepalive shell stays invisible and inert to Mission Control`() {
         let keepaliveShell = NSWindow(
             contentRect: NSRect(x: 0, y: 0, width: 500, height: 500),
             styleMask: [.titled],
@@ -16,14 +16,27 @@ struct SettingsWindowOpeningTests {
 
         #expect(keepaliveShell.identifier?.rawValue == "CodexBarLifecycleKeepalive")
         #expect(keepaliveShell.styleMask == [.borderless])
+        #expect(keepaliveShell.level == .normal)
+        #expect(keepaliveShell.collectionBehavior == [.auxiliary, .ignoresCycle, .transient])
+        #expect(!keepaliveShell.collectionBehavior.contains(.canJoinAllSpaces))
+        #expect(keepaliveShell.isExcludedFromWindowsMenu)
+        #expect(!keepaliveShell.isOpaque)
         #expect(keepaliveShell.alphaValue == 0)
+        #expect(!keepaliveShell.hasShadow)
+        #expect(keepaliveShell.ignoresMouseEvents)
+        #expect(!keepaliveShell.canHide)
         #expect(keepaliveShell.frame.size == NSSize(width: 1, height: 1))
+        #expect(keepaliveShell.frame.origin == NSPoint(x: -5000, y: -5000))
+    }
 
+    @Test
+    func `missing keepalive relay invokes settings fallback`() {
         let settingsWindow = NSWindow(
             contentRect: NSRect(x: 0, y: 0, width: 640, height: 480),
             styleMask: [.titled],
             backing: .buffered,
             defer: false)
+
         var presentedWindow: NSWindow?
         var prepareCount = 0
         let opener = SettingsWindowOpener(