Fix native fullscreen unreachable on the main window (#5933)

Sources/App/CmuxMainWindow.swift

@@ -69,6 +69,58 @@ final class CmuxMainWindow: NSWindow {
         return frame
     }
 
+    /// cmux creates its main window programmatically (never from a nib), so it
+    /// cannot inherit fullscreen capability from Interface Builder and instead
+    /// relied on AppKit *implicitly* granting `.fullScreenPrimary` to a
+    /// resizable, titled window. That implicit grant is not reliable across
+    /// macOS versions / display arrangements: on macOS 26 (Tahoe) a
+    /// freshly-created window reports an empty collection behavior
+    /// (`rawValue == 0`) and AppKit does not treat it as fullscreen-capable, so
+    /// Toggle Full Screen / ⌃⌘F / the green traffic-light button all fail to
+    /// enter a native fullscreen Space — the green button only zooms (#5933).
+    ///
+    /// Declaring `.fullScreenPrimary` here makes native fullscreen reachable
+    /// regardless of the OS's implicit default. It is idempotent where AppKit
+    /// would have granted it anyway, and composes with the temporary
+    /// `.fullScreenDisallowsTiling` opt-out the window factory applies when
+    /// spawning a window out of an existing fullscreen Space.
+    override init(
+        contentRect: NSRect,
+        styleMask: NSWindow.StyleMask,
+        backing: NSWindow.BackingStoreType,
+        defer flag: Bool
+    ) {
+        super.init(
+            contentRect: contentRect,
+            styleMask: styleMask,
+            backing: backing,
+            defer: flag
+        )
+        collectionBehavior = Self.canonicalCollectionBehavior(collectionBehavior)
+    }
+
+    @available(*, unavailable)
+    required init?(coder: NSCoder) {
+        fatalError("init(coder:) has not been implemented")
+    }
+
+    /// Returns `base` guaranteed to carry `.fullScreenPrimary` (and never
+    /// `.fullScreenNone`) so a cmux main window can always enter a native
+    /// fullscreen Space. Pure and `nonisolated` so it can be unit-tested
+    /// without constructing a window; see ``init(contentRect:styleMask:backing:defer:)``
+    /// for why declaring the capability explicitly is required.
+    nonisolated static func canonicalCollectionBehavior(
+        _ base: NSWindow.CollectionBehavior
+    ) -> NSWindow.CollectionBehavior {
+        var behavior = base
+        // `.fullScreenNone` and `.fullScreenPrimary` are mutually exclusive;
+        // drop any stale "none" before declaring primary so fullscreen is not
+        // suppressed.
+        behavior.remove(.fullScreenNone)
+        behavior.insert(.fullScreenPrimary)
+        return behavior
+    }
+
     private var isSoftHiddenForVisibilityController = false
 
     func setSoftHiddenForVisibilityController(_ isSoftHidden: Bool) {

cmux.xcodeproj/project.pbxproj

@@ -302,6 +302,7 @@
 		E7E00000000000000000000B /* CmuxLifecycleEventPublishing.swift in Sources */ = {isa = PBXBuildFile; fileRef = E7E00000000000000000000C /* CmuxLifecycleEventPublishing.swift */; };
 		2F0C07000000000000000002 /* CmuxMainWindow.swift in Sources */ = {isa = PBXBuildFile; fileRef = 2F0C07000000000000000001 /* CmuxMainWindow.swift */; };
 		D36090010000000000000005 /* CmuxMainWindowConstrainFrameTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = D36090010000000000000006 /* CmuxMainWindowConstrainFrameTests.swift */; };
+		D36090020000000000000005 /* CmuxMainWindowFullScreenCapabilityTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = D36090020000000000000006 /* CmuxMainWindowFullScreenCapabilityTests.swift */; };
 		799F1BEF876006EEB8CD1035 /* CMUXMobileCore in Frameworks */ = {isa = PBXBuildFile; productRef = EFB18E3B3099DFE2ECA3C263 /* CMUXMobileCore */; };
 		EFB18E3C0000000000000001 /* CMUXMobileCore in Frameworks */ = {isa = PBXBuildFile; productRef = EFB18E3B3099DFE2ECA3C263 /* CMUXMobileCore */; };
 		CA1F0A01CA1F0A01CA1F0A01 /* CmuxModalAlertPresentation.swift in Sources */ = {isa = PBXBuildFile; fileRef = CA1F0A02CA1F0A02CA1F0A02 /* CmuxModalAlertPresentation.swift */; };
@@ -1450,6 +1451,7 @@
 		E7E00000000000000000000C /* CmuxLifecycleEventPublishing.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = CmuxLifecycleEventPublishing.swift; sourceTree = "<group>"; };
 		2F0C07000000000000000001 /* CmuxMainWindow.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = App/CmuxMainWindow.swift; sourceTree = "<group>"; };
 		D36090010000000000000006 /* CmuxMainWindowConstrainFrameTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = CmuxMainWindowConstrainFrameTests.swift; sourceTree = "<group>"; };
+		D36090020000000000000006 /* CmuxMainWindowFullScreenCapabilityTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = CmuxMainWindowFullScreenCapabilityTests.swift; sourceTree = "<group>"; };
 		CA1F0A02CA1F0A02CA1F0A02 /* CmuxModalAlertPresentation.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = CmuxModalAlertPresentation.swift; sourceTree = "<group>"; };
 		C0DE31390000000000000102 /* CMUXOpenCommandTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = CMUXOpenCommandTests.swift; sourceTree = "<group>"; };
 		C0DE31390000000000000112 /* CMUXOpenHTMLFocusTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = CMUXOpenHTMLFocusTests.swift; sourceTree = "<group>"; };
@@ -3235,6 +3237,7 @@
 				A50019B3 /* SettingsSearchIndexTests.swift */,
 				D36090010000000000000004 /* SettingsWindowPresenterTests.swift */,
 				D36090010000000000000006 /* CmuxMainWindowConstrainFrameTests.swift */,
+				D36090020000000000000006 /* CmuxMainWindowFullScreenCapabilityTests.swift */,
 				970226F3C99D0D937CD00539 /* BrowserConfigTests.swift */,
 				BABA25000000000000000006 /* BrowserHTTPBasicAuthPromptCoordinatorTests.swift */,
 				BABA25000000000000000004 /* BrowserHTTPBasicAuthPromptTests.swift */,
@@ -4693,6 +4696,7 @@
 				C1A2B3C4D5E6F70800000001 /* CmuxConfigTests.swift in Sources */,
 				E7E000000000000000000003 /* CmuxEventBusTests.swift in Sources */,
 				D36090010000000000000005 /* CmuxMainWindowConstrainFrameTests.swift in Sources */,
+				D36090020000000000000005 /* CmuxMainWindowFullScreenCapabilityTests.swift in Sources */,
 				C0DE31390000000000000101 /* CMUXOpenCommandTests.swift in Sources */,
 				C0DE31390000000000000111 /* CMUXOpenHTMLFocusTests.swift in Sources */,
 				C3677001000000000000001 /* CmuxSSHURLRequestTests.swift in Sources */,

cmuxTests/CmuxMainWindowFullScreenCapabilityTests.swift

@@ -0,0 +1,79 @@
+import AppKit
+import Testing
+
+#if canImport(cmux_DEV)
+@testable import cmux_DEV
+#elseif canImport(cmux)
+@testable import cmux
+#endif
+
+@MainActor
+@Suite("CmuxMainWindow native fullscreen capability")
+struct CmuxMainWindowFullScreenCapabilityTests {
+    // cmux creates its main window programmatically and never loaded fullscreen
+    // capability from a nib, so it historically relied on AppKit *implicitly*
+    // granting `.fullScreenPrimary` to a resizable, titled window. That implicit
+    // grant is not reliable across macOS versions / display arrangements: on
+    // macOS 26 (Tahoe) a freshly-created CmuxMainWindow reports an empty
+    // collection behavior (`rawValue == 0`) and AppKit does NOT treat it as
+    // fullscreen-capable — so `toggleFullScreen(_:)`, ⌃⌘F, and the green
+    // traffic-light button all fail to enter a native fullscreen Space (the
+    // green button only zooms). See issue #5933.
+    //
+    // A CmuxMainWindow must therefore *declare* `.fullScreenPrimary` itself so
+    // native fullscreen is reachable regardless of the OS's implicit default.
+    @Test func mainWindowDeclaresFullScreenPrimaryCapability() {
+        let window = CmuxMainWindow(
+            contentRect: NSRect(x: 0, y: 0, width: 800, height: 600),
+            styleMask: [.titled, .closable, .miniaturizable, .resizable, .fullSizeContentView],
+            backing: .buffered,
+            defer: false
+        )
+        window.isReleasedWhenClosed = false
+        defer {
+            window.orderOut(nil)
+            window.close()
+        }
+
+        #expect(
+            window.collectionBehavior.contains(.fullScreenPrimary),
+            "Main window must declare .fullScreenPrimary so native fullscreen is reachable"
+        )
+        #expect(
+            !window.collectionBehavior.contains(.fullScreenNone),
+            "Main window must never carry .fullScreenNone, which suppresses native fullscreen"
+        )
+    }
+
+    // The capability decision is a pure, screen-agnostic transform so it runs
+    // deterministically on CI regardless of the test host's display setup.
+
+    @Test func canonicalBehaviorAddsFullScreenPrimaryToEmptyBehavior() {
+        let result = CmuxMainWindow.canonicalCollectionBehavior([])
+        #expect(result.contains(.fullScreenPrimary))
+        #expect(!result.contains(.fullScreenNone))
+    }
+
+    @Test func canonicalBehaviorDropsStaleFullScreenNone() {
+        let result = CmuxMainWindow.canonicalCollectionBehavior([.fullScreenNone])
+        #expect(result.contains(.fullScreenPrimary))
+        #expect(!result.contains(.fullScreenNone))
+    }
+
+    @Test func canonicalBehaviorPreservesUnrelatedBehaviorBits() {
+        // The window factory may layer `.fullScreenDisallowsTiling` on top when
+        // spawning out of an existing fullscreen Space; canonicalization must
+        // not clobber that (or any other unrelated bit).
+        let base: NSWindow.CollectionBehavior = [.fullScreenDisallowsTiling, .moveToActiveSpace]
+        let result = CmuxMainWindow.canonicalCollectionBehavior(base)
+        #expect(result.contains(.fullScreenPrimary))
+        #expect(result.contains(.fullScreenDisallowsTiling))
+        #expect(result.contains(.moveToActiveSpace))
+    }
+
+    @Test func canonicalBehaviorIsIdempotent() {
+        let once = CmuxMainWindow.canonicalCollectionBehavior([])
+        let twice = CmuxMainWindow.canonicalCollectionBehavior(once)
+        #expect(once == twice)
+    }
+}