diff --git a/docs/TESTING.md b/docs/TESTING.md
index 3249b96..17a711a 100644
--- a/docs/TESTING.md
+++ b/docs/TESTING.md
@@ -623,3 +623,76 @@ launch, window placement, click alignment and edge panning before rollout.
 
 After installing the tested X11 and CoreGraphics binaries locally, the user
 reported that everything was working (2026-10-16). Fullscreen policy was unchanged.
+
+## VRR presentation regression (#46)
+
+```sh
+python3 -m unittest discover -s tests -p 'test_x11_vrr.py'
+```
+
+The host fixtures exercise the patched eligibility, X11 property updates and
+EGL surface ownership transitions. They cover hidden/titled/partial views,
+multiple views, parent recreation, child fallback and current-context handling.
+
+Build `build-riot-coregraphics-runtime.py`, `build-riot-x11-runtime.py` and
+`build-riot-metal-presentation.py` together. Stage all three updated frameworks
+(CoreGraphics, AppKit's X11 backend, QuartzCore) when testing isolated binaries.
+Run `riot-metal-presentation-check` with `RIOT_PRESENTATION_PARENT=1` to create
+an owned borderless game-like window. It verifies the parent drawable is
+borrowed. Add `RIOT_PRESENTATION_RESIZE=1` to verify fallback to a child at
+half width and borrowing the parent again when restored. Add
+`RIOT_PRESENTATION_NESTED=1` for nested layers.
+The default probe still exercises the independent child-window path.
+
+For physical VRR validation, enable adaptive sync in the monitor and desktop,
+then manually test fullscreen and borderless League with a frame cap inside
+the monitor's VRR range (for example 157 FPS on a 165 Hz display), with VSync
+off. Check the monitor's live refresh display as well as the game FPS counter.
+Also test leaving fullscreen, restoring it, resizing, and alt-tab. Report GPU,
+driver, compositor and session type. A stable FPS counter or the X11 property
+alone does not prove that the monitor is using variable refresh.
+
+Local native validation on 2026-10-19 passed all three modes (child, parent
+with resize, nested parent with resize), including Vulkan-to-GL pixel readback
+and ten presentations per mode, using staged frameworks in a private prefix.
+Physical VRR and in-game performance on the reporter's Mutter setup remain
+unverified.
+
+## Metal VSync regression (#46)
+
+```sh
+python3 -m unittest discover -s tests -p 'test_metal_vsync.py'
+```
+
+These host checks compile the patched layer-tree policy, flush body and CGL
+swap methods against inert fixtures. They cover nested layers, VSync toggles,
+shared-window requests, independent contexts, late attachment and failed
+context/interval changes. They do not measure physical display refresh.
+
+For manual validation after updating with the clients closed, compare the
+same scene with in-game VSync on and off. With VSync on, presentation should
+follow the display/compositor cadence; with it off, the game's frame cap
+should continue to work. Record monitor refresh, compositor, X11/Xwayland,
+GPU/driver and window mode. The window presentation probe above checks the
+API wiring; an in-game/compositor timing comparison remains necessary.
+
+## Combined VSync and VRR testing
+
+The `test/vsync-vrr` branch combines PRs #81 and #88, resolving their shared
+compositor-patch and presentation-probe changes. The probe toggles
+`displaySyncEnabled` and checks the CGL interval in child, parent and nested
+parent modes; the parent modes also support resize fallback/restoration.
+All three native modes passed locally in a private prefix, together with ten
+host regression checks and validation of all 31 component patches.
+
+After closing the game and both clients:
+
+```sh
+git fetch origin
+git switch --track origin/test/vsync-vrr
+./scripts/update.sh
+```
+
+Test VSync with desktop VRR disabled, then test VRR with VSync off and a cap
+inside the monitor's adaptive range. Finally test both enabled. Report game
+FPS and the monitor's live refresh reading separately.
diff --git a/docs/TROUBLESHOOTING.md b/docs/TROUBLESHOOTING.md
index 3574291..a655648 100644
--- a/docs/TROUBLESHOOTING.md
+++ b/docs/TROUBLESHOOTING.md
@@ -541,3 +541,40 @@ Recovery requires every matching client to be at least 60 seconds old and a
 complete Hyprland window record (`class`, `title`, `mapped`, `hidden`). A second
 process scan after window inspection must find the same client identities and
 no game. Missing information or shutdown failure leaves normal launch in charge.
+
+## Variable refresh rate (VRR)
+
+Full-window borderless game layers now use the opaque managed X11 parent
+surface for presentation. Previously they swapped an independent child while
+the managed parent remained static. Using one surface lets the compositor
+track the game's updates for VRR and avoids scanning out an empty parent.
+Partial views, titled windows and other applications retain child drawables.
+The child fallback retains the compositor-bypass prohibition that prevents
+black screens. The fullscreen parent path advertises `_VARIABLE_REFRESH=1`;
+leaving fullscreen clears that request. Desktop/driver policy still decides
+whether to enable adaptive sync.
+
+With the game and both clients closed, rebuild with `./scripts/update.sh`;
+CoreGraphics, QuartzCore and the X11 backend must be updated together. Enable
+VRR in the desktop and monitor, and compare the monitor's live refresh reading
+to a frame cap below its maximum refresh, initially with VSync off. VRR and
+VSync are separate: this change does not implement an in-game frame limiter.
+See [the VRR probe and manual checks](TESTING.md#vrr-presentation-regression-46).
+
+Standalone child, parent and nested-parent presentation probes passed locally;
+monitor-level VRR and the reporter's in-game behavior still need confirmation.
+
+## VSync and frame caps (#46)
+
+The Metal layer's `displaySyncEnabled` property previously had no effect on
+the window swap interval. A game that delegates pacing to VSync could run
+uncapped when VSync was enabled. The compositor now applies that property to
+the window before swapping, including nested Metal layers and setting changes.
+If several Metal layers share a window, any layer requesting VSync enables it
+for that window. Other windows retain independent swap settings.
+
+Exit the game and both clients, then run `./scripts/update.sh` to rebuild and
+install the QuartzCore and OpenGL changes. Until updated, disable in-game
+VSync to use the game's frame cap, as the issue reporter confirmed. Physical
+scanout timing still depends on the driver and desktop compositor; the fix
+has standalone regression coverage but needs an in-game timing retest.
diff --git a/patches/cocotron.patch b/patches/cocotron.patch
index 85aa08f..cc6452b 100644
--- a/patches/cocotron.patch
+++ b/patches/cocotron.patch
@@ -5031,7 +5031,7 @@ index 0000000..31fa646
 +
 +#endif
 diff --git a/AppKit/X11.backend/X11Window.h b/AppKit/X11.backend/X11Window.h
-index bfe3839a..48cfac4c 100644
+index bfe3839a..bc592711 100644
 --- a/AppKit/X11.backend/X11Window.h
 +++ b/AppKit/X11.backend/X11Window.h
 @@ -26,7 +26,7 @@
@@ -5043,7 +5043,7 @@ index bfe3839a..48cfac4c 100644
  
  @interface X11Window : CGWindow {
      int _level; // TODO: care about this value
-@@ -47,8 +47,32 @@
+@@ -47,8 +47,33 @@
      BOOL _mapped;
      CGPoint _lastMotionPos;
      BOOL _isModal;
@@ -5053,6 +5053,7 @@ index bfe3839a..48cfac4c 100644
 +    BOOL _hasAlpha; // created with the 32-bit ARGB visual
 +    BOOL _wasMapped; // the visual is settled at the first map
      BOOL _hasShadow;
++    id _layerDrawableOwner;
 +    NSTimer *_remoteFrameTimer;
 +    Window _remoteFrameWindow;
 +    GC _remoteFrameGC;
@@ -5076,19 +5077,22 @@ index bfe3839a..48cfac4c 100644
  
  @public
      XIC _xic;
-@@ -60,9 +84,9 @@
+@@ -60,9 +85,12 @@
  - (Visual *) visual;
  - (Drawable) drawable;
  - (NSPoint) transformPoint: (NSPoint) pos;
 -- (O2Rect) transformFrame: (O2Rect) frame;
  
  - (Window) windowHandle;
++- (void *) layerDrawableFor: (id) owner;
++- (void) acquireLayerDrawable: (id) owner;
++- (void) releaseLayerDrawable: (id) owner;
 +- (BOOL) handleRemoteFrameExpose: (Window) window;
  
  - (void) frameChanged;
  - (void) setLastKnownCursorPosition: (CGPoint) point;
 diff --git a/AppKit/X11.backend/X11Window.m b/AppKit/X11.backend/X11Window.m
-index f4925b66..e458d96f 100644
+index f4925b6..b565b91 100644
 --- a/AppKit/X11.backend/X11Window.m
 +++ b/AppKit/X11.backend/X11Window.m
 @@ -18,11 +18,14 @@
@@ -5455,7 +5459,7 @@ index f4925b66..e458d96f 100644
  }
  
  - (void) dealloc {
-@@ -279,24 +498,30 @@ static NSData *makeWindowIcon() {
+@@ -279,24 +498,59 @@ static NSData *makeWindowIcon() {
      return _styleMask;
  }
  
@@ -5492,6 +5496,35 @@ index f4925b66..e458d96f 100644
      }
 +    return NO;
 +}
++
++/* Keep the game on one opaque managed surface. Mutter's VRR frame clock
++ * follows that surface's repaint events, not an independently swapped child.
++ * _VARIABLE_REFRESH also advertises eligibility to X11 drivers that use it. */
++- (void) updateLayerPresentationHints: (BOOL) fullscreen {
++    if (!X11IsLeagueGameWindow(_display, _window, _delegate)) return;
++    unsigned long adaptive = fullscreen && _layerDrawableOwner != nil;
++    unsigned long bypass = fullscreen && !_layerDrawableOwner ? 2 : 0;
++    XChangeProperty(_display, _window, XInternAtom(_display, "_VARIABLE_REFRESH", False),
++                    XA_CARDINAL, 32, PropModeReplace, (unsigned char *)&adaptive, 1);
++    XChangeProperty(_display, _window, XInternAtom(_display, "_NET_WM_BYPASS_COMPOSITOR", False),
++                    XA_CARDINAL, 32, PropModeReplace, (unsigned char *)&bypass, 1);
++}
++
++- (void *) layerDrawableFor: (id) owner {
++    return (!_layerDrawableOwner || _layerDrawableOwner == owner) && !_hasAlpha && X11IsLeagueGameWindow(_display, _window, _delegate) ? _cglWindow : NULL;
++}
++
++- (void) acquireLayerDrawable: (id) owner {
++    if (_layerDrawableOwner && _layerDrawableOwner != owner) return;
++    _layerDrawableOwner = owner;
++    [self updateLayerPresentationHints: _fullscreenRequested];
++}
++
++- (void) releaseLayerDrawable: (id) owner {
++    if (_layerDrawableOwner != owner) return;
++    _layerDrawableOwner = nil;
++    [self updateLayerPresentationHints: _fullscreenRequested];
++}
  
 +- (void) requestFullscreen: (BOOL) fullscreen force: (BOOL) force {
 +    if (fullscreen) {
@@ -5502,7 +5535,7 @@ index f4925b66..e458d96f 100644
      if (!_mapped) {
          long states[2];
          int states_cnt = 0;
-@@ -304,7 +529,7 @@ static NSData *makeWindowIcon() {
+@@ -304,7 +558,7 @@ static NSData *makeWindowIcon() {
              states[states_cnt++] =
                      (long) XInternAtom(_display, "_NET_WM_STATE_MODAL", False);
          }
@@ -5511,7 +5544,7 @@ index f4925b66..e458d96f 100644
              states[states_cnt++] = (long) XInternAtom(
                      _display, "_NET_WM_STATE_FULLSCREEN", False);
          }
-@@ -312,14 +537,13 @@ static NSData *makeWindowIcon() {
+@@ -312,14 +566,13 @@ static NSData *makeWindowIcon() {
                          XInternAtom(_display, "_NET_WM_STATE", False), XA_ATOM,
                          32, PropModeReplace, (const unsigned char *) states,
                          states_cnt);
@@ -5528,11 +5561,12 @@ index f4925b66..e458d96f 100644
          event.data.l[1] =
                  (long) XInternAtom(_display, "_NET_WM_STATE_FULLSCREEN", False);
          event.data.l[3] = 1;
-@@ -327,6 +551,47 @@ static NSData *makeWindowIcon() {
+@@ -327,6 +580,48 @@ static NSData *makeWindowIcon() {
                     SubstructureNotifyMask | SubstructureRedirectMask,
                     (XEvent *) &event);
      }
 +    _fullscreenRequested = fullscreen;
++    [self updateLayerPresentationHints: fullscreen];
 +    XFlush(_display);
 +}
 +
@@ -5576,7 +5610,7 @@ index f4925b66..e458d96f 100644
  }
  
  - (void) setStyleMask: (NSUInteger) mask {
-@@ -338,7 +603,6 @@ static NSData *makeWindowIcon() {
+@@ -338,7 +633,6 @@ static NSData *makeWindowIcon() {
  }
  
  + (void) removeDecorationForWindow: (Window) w onDisplay: (Display *) dpy {
@@ -5584,7 +5618,7 @@ index f4925b66..e458d96f 100644
      struct {
          unsigned long flags;
          unsigned long functions;
-@@ -356,11 +620,25 @@ static NSData *makeWindowIcon() {
+@@ -356,11 +650,25 @@ static NSData *makeWindowIcon() {
  
  - (void) ensureMapped {
      if (!_mapped) {
@@ -5610,7 +5644,7 @@ index f4925b66..e458d96f 100644
  - (void) showWindowWithoutActivation {
      [self ensureMapped];
  }
-@@ -377,15 +655,27 @@ static NSData *makeWindowIcon() {
+@@ -377,15 +685,27 @@ static NSData *makeWindowIcon() {
  - (void) syncDelegateProperties {
      long mask = KeyPressMask | KeyReleaseMask | ExposureMask |
                  StructureNotifyMask | EnterWindowMask | LeaveWindowMask |
@@ -5643,7 +5677,7 @@ index f4925b66..e458d96f 100644
      // TODO: background color
  }
  
-@@ -393,6 +683,28 @@ static NSData *makeWindowIcon() {
+@@ -393,6 +713,28 @@ static NSData *makeWindowIcon() {
      // This is essentially dealloc; we release our contexts
      // and windows, but unlike dealloc, this method can be called
      // several times, so set everything to nil/NULL/0.
@@ -5672,7 +5706,7 @@ index f4925b66..e458d96f 100644
      [_context release];
      _context = nil;
  
-@@ -421,6 +733,392 @@ static NSData *makeWindowIcon() {
+@@ -421,6 +763,392 @@ static NSData *makeWindowIcon() {
      }
  }
  
@@ -6065,7 +6099,7 @@ index f4925b66..e458d96f 100644
  - (Window) windowHandle {
      return _window;
  }
-@@ -470,14 +1168,32 @@ static NSData *makeWindowIcon() {
+@@ -470,14 +1198,32 @@ static NSData *makeWindowIcon() {
      const char *text = [title cString];
      XStringListToTextProperty((char **) &text, 1, &prop);
      XSetWMName(_display, _window, &prop);
@@ -6099,7 +6133,7 @@ index f4925b66..e458d96f 100644
  }
  
  - (void) setHasShadow: (BOOL) value {
-@@ -488,6 +1204,25 @@ static NSData *makeWindowIcon() {
+@@ -488,6 +1234,25 @@ static NSData *makeWindowIcon() {
      _level = value;
  }
  
@@ -6125,7 +6159,7 @@ index f4925b66..e458d96f 100644
  - (void) setOpaque: (BOOL) value {
      _isOpaque = value;
  }
-@@ -518,7 +1253,7 @@ static NSData *makeWindowIcon() {
+@@ -518,7 +1283,7 @@ static NSData *makeWindowIcon() {
  
  - (void) placeAboveWindow: (NSInteger) otherNumber {
      X11Window *other = [X11Window windowWithWindowNumber: otherNumber];
@@ -6134,7 +6168,7 @@ index f4925b66..e458d96f 100644
  
      if (!other) {
          XRaiseWindow(_display, _window);
-@@ -530,7 +1265,7 @@ static NSData *makeWindowIcon() {
+@@ -530,7 +1295,7 @@ static NSData *makeWindowIcon() {
  
  - (void) placeBelowWindow: (NSInteger) otherNumber {
      X11Window *other = [X11Window windowWithWindowNumber: otherNumber];
@@ -6143,7 +6177,7 @@ index f4925b66..e458d96f 100644
  
      if (!other) {
          XLowerWindow(_display, _window);
-@@ -541,8 +1276,23 @@ static NSData *makeWindowIcon() {
+@@ -541,8 +1306,23 @@ static NSData *makeWindowIcon() {
  }
  
  - (void) makeKey {
@@ -6168,7 +6202,7 @@ index f4925b66..e458d96f 100644
  }
  
  - (void) makeMain {
-@@ -559,7 +1309,29 @@ static NSData *makeWindowIcon() {
+@@ -559,7 +1339,29 @@ static NSData *makeWindowIcon() {
      XRaiseWindow(_display, _window);
  }
  
@@ -6198,7 +6232,7 @@ index f4925b66..e458d96f 100644
      Atom wmState = XInternAtom(_display, "_NET_WM_STATE", FALSE);
      Atom hiddenState = XInternAtom(_display, "_NET_WM_STATE_HIDDEN", FALSE);
  
-@@ -593,8 +1365,10 @@ static NSData *makeWindowIcon() {
+@@ -593,8 +1395,10 @@ static NSData *makeWindowIcon() {
      if (_cglContext == NULL) {
          CGLError error;
  
@@ -6211,10 +6245,12 @@ index f4925b66..e458d96f 100644
              NSLog(@"CGLCreateContext failed at %s %d with error %d", __FILE__,
                    __LINE__, error);
  
-@@ -615,6 +1389,12 @@ static NSData *makeWindowIcon() {
+@@ -615,6 +1419,14 @@ static NSData *makeWindowIcon() {
  }
  
  - (void) openGLFlushBuffer {
++    // QuartzCore owns presentation while a full-window game layer borrows it.
++    if (_layerDrawableOwner) return;
 +    /* A remote compositor surface owns this drawable while it is present.
 +     * Swapping the local Onyx surface would erase it until the next timer
 +     * tick. Keep local presentation for windows without a usable remote frame. */
@@ -6224,7 +6260,7 @@ index f4925b66..e458d96f 100644
      CGLError error;
  
      CGLContextObj prevContext = CGLGetCurrentContext();
-@@ -652,7 +1432,7 @@ static NSData *makeWindowIcon() {
+@@ -652,7 +1464,7 @@ static NSData *makeWindowIcon() {
  }
  
  - (O2Rect) frame {
@@ -6233,7 +6269,7 @@ index f4925b66..e458d96f 100644
  }
  
  static int ignoreBadWindow(Display *display, XErrorEvent *errorEvent) {
-@@ -666,6 +1446,7 @@ static int ignoreBadWindow(Display *display, XErrorEvent *errorEvent) {
+@@ -666,6 +1478,7 @@ static int ignoreBadWindow(Display *display, XErrorEvent *errorEvent) {
  }
  
  - (void) frameChanged {
@@ -6241,7 +6277,7 @@ index f4925b66..e458d96f 100644
      XErrorHandler previousHandler = XSetErrorHandler(ignoreBadWindow);
      @try {
          Window root, parent;
-@@ -710,19 +1491,13 @@ static int ignoreBadWindow(Display *display, XErrorEvent *errorEvent) {
+@@ -710,19 +1523,13 @@ static int ignoreBadWindow(Display *display, XErrorEvent *errorEvent) {
      [_deviceDictionary addEntriesFromDictionary: entries];
  }
  
@@ -9629,13 +9665,13 @@ index 5dcac115..5de4f03f 100644
 +
  @end
 diff --git a/QuartzCore/CALayerContext.m b/QuartzCore/CALayerContext.m
-index 5dce8c5..3a7f937 100644
 --- a/QuartzCore/CALayerContext.m
 +++ b/QuartzCore/CALayerContext.m
-@@ -1,47 +1,77 @@
+@@ -1,47 +1,89 @@
  #import <Foundation/NSString.h>
 +#import <Foundation/NSMutableArray.h>
  #import <QuartzCore/CALayer.h>
++#import <QuartzCore/CAMetalLayer.h>
  #import <QuartzCore/CALayerContext.h>
  #import <QuartzCore/CARenderer.h>
  #import "CALayerInternal.h"
@@ -9657,6 +9693,17 @@ index 5dce8c5..3a7f937 100644
 +    return NO;
 +}
 +
++static GLint metalSwapInterval(CALayer *layer) {
++    GLint interval = -1;
++    if ([[layer class] isSubclassOfClass: [CAMetalLayerInternal class]])
++        interval = [(CAMetalLayer *)layer displaySyncEnabled] ? 1 : 0;
++    for (CALayer *child in layer.sublayers) {
++        GLint childInterval = metalSwapInterval(child);
++        if (childInterval > interval) interval = childInterval;
++    }
++    return interval;
++}
++
 +/* The X11 transport presents Chromium's flattened full-window surface.
 + * Avoid uploading and compositing that same window again into a covered GL
 + * child. Restrict this to the explicitly configured native presentation path. */
@@ -9700,10 +9747,11 @@ index 5dce8c5..3a7f937 100644
 -        kCGLNoError)
 -        NSLog(@"CGLCreateContext failed with %d in %s %d", error, __FILE__,
 -              __LINE__);
+-
 +    self = [super init];
 +    if (self == nil)
 +        return nil;
- 
++
 +    _deleteTextureIds = [[NSMutableArray alloc] init];
      _frame = rect;
 -
@@ -9722,14 +9770,15 @@ index 5dce8c5..3a7f937 100644
 +    [_deleteTextureIds release];
      [_renderer release];
      CGLReleaseContext(_glContext);
+-    CGLDestroyWindow(_cglWindow);
 +    CGLReleasePixelFormat(_pixelFormat);
-     CGLDestroyWindow(_cglWindow);
++    if (_ownsCglWindow) CGLDestroyWindow(_cglWindow);
      [_subwindow release];
 -    [_layer release];
      [super dealloc];
  }
  
-@@ -51,12 +81,22 @@
+@@ -51,12 +93,22 @@
  }
  
  - (void) setLayer: (CALayer *) layer {
@@ -9752,12 +9801,18 @@ index 5dce8c5..3a7f937 100644
  }
  
  - (void) setSubwindow: (CGSubWindow*) subwindow
-@@ -68,16 +108,50 @@
+@@ -64,20 +116,55 @@
+     CGSubWindow* oldSubwindow = _subwindow;
+ 
+     if (_cglWindow) {
+-        CGLDestroyWindow(_cglWindow);
++        if (_ownsCglWindow) CGLDestroyWindow(_cglWindow);
      }
  
      _subwindow = [subwindow retain];
 -    _cglWindow = CGLGetWindow([_subwindow nativeWindow]);
 +    _cglWindow = NULL;
++    _ownsCglWindow = NO;
 +    if (_subwindow != nil) {
 +        if (_glContext == NULL) {
 +            CGLPixelFormatAttribute attributes[] = { 0 };
@@ -9776,7 +9831,7 @@ index 5dce8c5..3a7f937 100644
 +            }
 +        }
 +        if (_glContext != NULL)
-+            _cglWindow = CGLGetWindow([_subwindow nativeWindow]);
++            [self updateDrawable];
 +    }
  
      [_subwindow show];
@@ -9804,7 +9859,7 @@ index 5dce8c5..3a7f937 100644
  }
  
  - (void) assignTextureIdsToLayerTree: (CALayer *) layer {
-@@ -93,8 +167,27 @@
+@@ -93,8 +180,43 @@
          [self assignTextureIdsToLayerTree: child];
  }
  
@@ -9821,6 +9876,22 @@ index 5dce8c5..3a7f937 100644
 +    for (CALayer *child in layer.sublayers)
 +        [self prepareMetalLayers: child];
 +}
++
++- (void) updateDrawable {
++    if (!_subwindow || !_glContext) return;
++    [_subwindow setAllowsParentDrawable: hasMetalLayer(_layer)];
++    void *shared = [_subwindow sharedCGLWindow];
++    if (shared && shared == _cglWindow && !_ownsCglWindow) return;
++    if (!shared && _cglWindow && _ownsCglWindow) return;
++    CGLContextObj previous = CGLGetCurrentContext();
++    if (previous == _glContext) CGLSetCurrentContext(NULL);
++    if (_ownsCglWindow) CGLDestroyWindow(_cglWindow);
++    _cglWindow = shared ? shared : CGLGetWindow([_subwindow nativeWindow]);
++    _ownsCglWindow = !shared && _cglWindow != NULL;
++    // Update CGL's surface binding even when another context was current.
++    CGLContextMakeCurrentAndAttachToWindow(_glContext, _cglWindow);
++    if (previous != _glContext) CGLSetCurrentContext(previous);
++}
 +
  - (void) renderLayer: (CALayer *) layer {
 +    CFTimeInterval renderLayerStart = CACurrentMediaTime();
@@ -9832,28 +9903,31 @@ index 5dce8c5..3a7f937 100644
  
      glEnable(GL_DEPTH_TEST);
      glShadeModel(GL_SMOOTH);
-@@ -118,27 +211,62 @@
+@@ -118,27 +240,63 @@
  
      [_deleteTextureIds removeAllObjects];
  
 +    CFTimeInterval assignStart = CACurrentMediaTime();
 +    darlingQCTiming("renderLayerSetup", assignStart - renderLayerStart);
      [self assignTextureIdsToLayerTree: layer];
-+    darlingQCTiming("assignTextureIds", CACurrentMediaTime() - assignStart);
- 
+-
 -    // this is where the Metal layer renders to an internal texture for us to use
 -    if ([[layer class] isSubclassOfClass: [CAMetalLayerInternal class]]) {
 -        CAMetalLayerInternal* mtl = (CAMetalLayerInternal*)layer;
 -        [mtl prepareRender];
 -    }
+-
++    darlingQCTiming("assignTextureIds", CACurrentMediaTime() - assignStart);
++
 +    [self prepareMetalLayers: layer];
- 
++
 +    CFTimeInterval rendererStart = CACurrentMediaTime();
      [_renderer render];
 +    darlingQCTiming("rendererRender", CACurrentMediaTime() - rendererStart);
  }
  
  - (void) render {
++    [self updateDrawable];
 +    if (_cglWindow == NULL || _layer == nil)
 +        return;
 +    if(skipLocalRender(_layer, _frame.size))return;
@@ -9900,7 +9974,7 @@ index 5dce8c5..3a7f937 100644
  }
  
  - (void) startTimerIfNeeded {
-@@ -147,7 +275,7 @@
+@@ -147,7 +305,7 @@
                                                     target: self
                                                   selector: @selector(timer:)
                                                   userInfo: nil
@@ -9909,14 +9983,25 @@ index 5dce8c5..3a7f937 100644
  }
  
  - (void) deleteTextureId: (NSNumber *) textureId {
-@@ -155,7 +283,9 @@
+@@ -155,7 +313,20 @@
  }
  
  - (void) flush {
 -    CGLFlushDrawable(_glContext);
 +    if(skipLocalRender(_layer, _frame.size))return;
-+    if (_glContext != NULL && _cglWindow != NULL)
++    if (_glContext != NULL && _cglWindow != NULL) {
++        CGLContextObj previous = CGLGetCurrentContext();
++        // EGL applies the interval to the current draw surface, so attach this
++        // window before setting it (including after late window attachment).
++        if (CGLContextMakeCurrentAndAttachToWindow(_glContext, _cglWindow) != kCGLNoError)
++            return;
++        GLint interval = metalSwapInterval(_layer);
++        if (interval >= 0)
++            CGLSetParameter(_glContext, kCGLCPSwapInterval, &interval);
 +        CGLFlushDrawable(_glContext);
++        if (previous != _glContext)
++            CGLSetCurrentContext(previous);
++    }
  }
  
  @end
@@ -11242,10 +11327,14 @@ index 49b03483..5ebbf535 100644
  - (void) display;
  - (void) displayIfNeeded;
 diff --git a/QuartzCore/include/QuartzCore/CALayerContext.h b/QuartzCore/include/QuartzCore/CALayerContext.h
-index e4b0c342..d61c37ba 100644
+index e4b0c342..69b39250 100644
 --- a/QuartzCore/include/QuartzCore/CALayerContext.h
 +++ b/QuartzCore/include/QuartzCore/CALayerContext.h
-@@ -20,6 +20,7 @@
+@@ -17,9 +17,11 @@
+     NSTimer *_timer;
+     CGSubWindow* _subwindow;
+     void* _cglWindow;
++    BOOL _ownsCglWindow;
  }
  
  @property(readonly) CGLContextObj glContext;
@@ -11510,3 +11599,124 @@ index 53bacc46..3c6adfb7 100644
  - (void) beginSheetForDirectory: (NSString *) path
                             file: (NSString *) name
                   modalForWindow: (NSWindow *) docWindow
+diff --git a/CoreGraphics/CGSubWindow.m b/CoreGraphics/CGSubWindow.m
+index 008ccd74..6692deb5 100644
+--- a/CoreGraphics/CGSubWindow.m
++++ b/CoreGraphics/CGSubWindow.m
+@@ -8,6 +8,10 @@
+     return NULL;
+ }
+ 
++// Backends may lend an existing EGL surface for full-window layer rendering.
++- (void *) sharedCGLWindow { return NULL; }
++- (void) setAllowsParentDrawable: (BOOL) allowed {}
++
+ - (void) show {
+     O2InvalidAbstractInvocation();
+ }
+diff --git a/CoreGraphics/include/CoreGraphics/CGSubWindow.h b/CoreGraphics/include/CoreGraphics/CGSubWindow.h
+index de7a3496..79ee0d31 100644
+--- a/CoreGraphics/include/CoreGraphics/CGSubWindow.h
++++ b/CoreGraphics/include/CoreGraphics/CGSubWindow.h
+@@ -6,6 +6,9 @@
+ @interface CGSubWindow : NSObject
+ 
+ - (void *) nativeWindow;
++// Borrowed surface; the subwindow/backend retains ownership.
++- (void *) sharedCGLWindow;
++- (void) setAllowsParentDrawable: (BOOL) allowed;
+ 
+ - (void) show;
+ - (void) hide;
+diff --git a/AppKit/X11.backend/X11SubWindow.m b/AppKit/X11.backend/X11SubWindow.m
+index 738ab457..6596dab5 100644
+--- a/AppKit/X11.backend/X11SubWindow.m
++++ b/AppKit/X11.backend/X11SubWindow.m
+@@ -1,6 +1,7 @@
+ #import "X11SubWindow.h"
+ #import "X11Display.h"
+ #import "X11Window.h"
++#import <AppKit/NSWindow.h>
+ 
+ @implementation X11SubWindow
+ 
+@@ -15,8 +16,9 @@
+ }
+ 
+ - (id) initWithParentWindow: (X11Window *) parent frame: (CGRect) frame {
+-    _parent = parent;
++    _parent = [parent retain];
+     frame = [self convertFrame: frame];
++    _drawableFrame = frame;
+ 
+     _display = [(X11Display *) [NSDisplay currentDisplay] display];
+ 
+@@ -31,7 +33,9 @@
+ }
+ 
+ - (void) dealloc {
++    if (_usingParentDrawable) [_parent releaseLayerDrawable: self];
+     XDestroyWindow(_display, _window);
++    [_parent release];
+     [super dealloc];
+ }
+ 
+@@ -39,16 +43,41 @@
+     return (void *) _window;
+ }
+ 
++- (void) setAllowsParentDrawable: (BOOL) allowed {
++    _allowsParentDrawable = allowed;
++}
++
++- (void *) sharedCGLWindow {
++    // Only a full-window borderless game view may draw into the managed parent.
++    // Other views keep independent child drawables and their own coordinates.
++    CGRect parentFrame = [_parent frame];
++    BOOL coversParent = _allowsParentDrawable && _visible && !([_parent styleMask] & NSTitledWindowMask) &&
++        CGRectEqualToRect(_drawableFrame, CGRectMake(0, 0, parentFrame.size.width, parentFrame.size.height));
++    void *surface = coversParent ? [_parent layerDrawableFor: self] : NULL;
++    BOOL usingParent = surface != NULL;
++    if (usingParent != _usingParentDrawable) {
++        if (usingParent) [_parent acquireLayerDrawable: self];
++        else [_parent releaseLayerDrawable: self];
++        _usingParentDrawable = usingParent;
++    }
++    if (_visible && !usingParent) XMapWindow(_display, _window);
++    else XUnmapWindow(_display, _window);
++    return surface;
++}
++
+ - (void) show {
+-    XMapWindow(_display, _window);
++    _visible = YES;
++    [self sharedCGLWindow];
+ }
+ 
+ - (void) hide {
+-    XUnmapWindow(_display, _window);
++    _visible = NO;
++    [self sharedCGLWindow];
+ }
+ 
+ - (void) setFrame: (CGRect) frame {
+     frame = [self convertFrame: frame];
++    _drawableFrame = frame;
+ 
+     XMoveResizeWindow(_display, _window, frame.origin.x, frame.origin.y,
+                       frame.size.width, frame.size.height);
+diff --git a/AppKit/X11.backend/X11SubWindow.h b/AppKit/X11.backend/X11SubWindow.h
+index 65b63a3e..e5b913b1 100644
+--- a/AppKit/X11.backend/X11SubWindow.h
++++ b/AppKit/X11.backend/X11SubWindow.h
+@@ -7,6 +7,10 @@
+     X11Window *_parent;
+     Display *_display;
+     Window _window;
++    CGRect _drawableFrame;
++    BOOL _visible;
++    BOOL _allowsParentDrawable;
++    BOOL _usingParentDrawable;
+ }
+ 
+ - initWithParentWindow: (X11Window *) parent frame: (CGRect) frame;
diff --git a/patches/darling.patch b/patches/darling.patch
index ae2cfd8..a4d2178 100644
--- a/patches/darling.patch
+++ b/patches/darling.patch
@@ -6765,7 +6765,7 @@ index deca16b87..d75d5e22d 100644
  
  set_property(TARGET OpenGL APPEND_STRING PROPERTY LINK_FLAGS
 diff --git a/src/frameworks/OpenGL/OpenGL.c b/src/frameworks/OpenGL/OpenGL.c
-index ffd7fe054..f25fd9aa5 100644
+index ffd7fe054..a40a634d3 100644
 --- a/src/frameworks/OpenGL/OpenGL.c
 +++ b/src/frameworks/OpenGL/OpenGL.c
 @@ -2,11 +2,22 @@
@@ -6866,7 +6866,7 @@ index ffd7fe054..f25fd9aa5 100644
  static EGLConfig config;
  static int num_config;
  
-@@ -48,10 +124,18 @@ struct _CGLContextObj {
+@@ -48,10 +124,19 @@ struct _CGLContextObj {
      GLuint retain_count;
      pthread_mutex_t lock;
      EGLContext egl_context;
@@ -6876,6 +6876,7 @@ index ffd7fe054..f25fd9aa5 100644
      // EGL has no function for getting the current swap interval,
      // so we need to save the last set value. The default is 1.
      int swap_interval;
++    int swap_interval_requested;
 +    EGLSurface native_present_surface;
 +    EGLContext native_present_context;
 +    DarlingNativePresentTarget *native_present_target;
@@ -6885,7 +6886,7 @@ index ffd7fe054..f25fd9aa5 100644
  };
  
  struct _CGLPixelFormatObj {
-@@ -59,6 +143,24 @@ struct _CGLPixelFormatObj {
+@@ -59,6 +144,24 @@ struct _CGLPixelFormatObj {
      CGLPixelFormatAttribute *attributes;
  };
  
@@ -6910,7 +6911,7 @@ index ffd7fe054..f25fd9aa5 100644
  static inline int attribute_has_argument(CGLPixelFormatAttribute attr) {
      switch (attr) {
      case kCGLPFAAuxBuffers:
-@@ -69,6 +171,9 @@ static inline int attribute_has_argument(CGLPixelFormatAttribute attr) {
+@@ -69,6 +172,9 @@ static inline int attribute_has_argument(CGLPixelFormatAttribute attr) {
      case kCGLPFAAccumSize:
      case kCGLPFARendererID:
      case kCGLPFADisplayMask:
@@ -6920,7 +6921,7 @@ index ffd7fe054..f25fd9aa5 100644
          return 1;
      default:
          return 0;
-@@ -78,6 +183,7 @@ static inline int attribute_has_argument(CGLPixelFormatAttribute attr) {
+@@ -78,6 +184,7 @@ static inline int attribute_has_argument(CGLPixelFormatAttribute attr) {
  __attribute__((constructor))
  static void _CGLInitialize(void)
  {
@@ -6928,7 +6929,7 @@ index ffd7fe054..f25fd9aa5 100644
      g_displays = CFDictionaryCreateMutable(NULL, 0, NULL, NULL);
  }
  
-@@ -93,41 +199,71 @@ static int attributes_count(const CGLPixelFormatAttribute *attrs) {
+@@ -93,41 +200,71 @@ static int attributes_count(const CGLPixelFormatAttribute *attrs) {
  
  CGLError CGLRegisterNativeDisplay(void *native_display) {
  
@@ -7008,7 +7009,7 @@ index ffd7fe054..f25fd9aa5 100644
  
          pthread_mutex_lock(&g_displaysMutex);
          CFDictionaryAddValue(g_displays, (const void*)(unsigned long) cid, rv);
-@@ -139,6 +275,8 @@ static struct _CGLDisplay* getCGLDisplay(CGSConnectionID cid)
+@@ -139,6 +276,8 @@ static struct _CGLDisplay* getCGLDisplay(CGSConnectionID cid)
  
  CGLError CGLSetSurface(CGLContextObj gl, CGSConnectionID cid, CGSWindowID wid, CGSSurfaceID sid)
  {
@@ -7017,7 +7018,7 @@ index ffd7fe054..f25fd9aa5 100644
      struct _CGLDisplay* disp = getCGLDisplay(cid);
      if (!disp)
          return kCGLBadConnection;
-@@ -152,7 +290,7 @@ CGLError CGLSetSurface(CGLContextObj gl, CGSConnectionID cid, CGSWindowID wid, C
+@@ -152,7 +291,7 @@ CGLError CGLSetSurface(CGLContextObj gl, CGSConnectionID cid, CGSWindowID wid, C
      if (!window)
          return kCGLBadWindow;
  
@@ -7026,7 +7027,7 @@ index ffd7fe054..f25fd9aa5 100644
      if (gl->egl_surface == EGL_NO_SURFACE)
          return kCGLBadState;
      return kCGLNoError;
-@@ -161,7 +299,7 @@ CGLError CGLSetSurface(CGLContextObj gl, CGSConnectionID cid, CGSWindowID wid, C
+@@ -161,7 +300,7 @@ CGLError CGLSetSurface(CGLContextObj gl, CGSConnectionID cid, CGSWindowID wid, C
  CGLWindowRef CGLGetWindow(void *native_window) {
  
      EGLNativeWindowType window = (EGLNativeWindowType) native_window;
@@ -7035,7 +7036,7 @@ index ffd7fe054..f25fd9aa5 100644
  
      if (surface == EGL_NO_SURFACE) {
          return NULL;
-@@ -170,15 +308,53 @@ CGLWindowRef CGLGetWindow(void *native_window) {
+@@ -170,15 +309,53 @@ CGLWindowRef CGLGetWindow(void *native_window) {
      return (CGLWindowRef) surface;
  }
  
@@ -7091,7 +7092,7 @@ index ffd7fe054..f25fd9aa5 100644
  }
  
  static pthread_key_t current_context_key;
-@@ -198,18 +374,42 @@ CGLContextObj CGLGetCurrentContext(void) {
+@@ -198,18 +375,42 @@ CGLContextObj CGLGetCurrentContext(void) {
      return pthread_getspecific(key);
  }
  
@@ -7139,7 +7140,7 @@ index ffd7fe054..f25fd9aa5 100644
  }
  
  CGLError CGLSetFullScreen(CGLContextObj ctx) {
-@@ -223,11 +423,13 @@ CGLError CGLChoosePixelFormat(
+@@ -223,11 +424,13 @@ CGLError CGLChoosePixelFormat(
      CGLPixelFormatObj *result,
      GLint *number_of_screens
  ) {
@@ -7154,7 +7155,7 @@ index ffd7fe054..f25fd9aa5 100644
      for (int i = 0; i < count; i++) {
          format->attributes[i] = attrs[i];
      }
-@@ -251,6 +453,10 @@ CGLError CGLDescribePixelFormat(
+@@ -251,6 +454,10 @@ CGLError CGLDescribePixelFormat(
      CGLPixelFormatAttribute attr,
      GLint *value
  ) {
@@ -7165,7 +7166,7 @@ index ffd7fe054..f25fd9aa5 100644
      for (int i = 0; format->attributes[i] != 0; i++) {
          int has_arg = attribute_has_argument(format->attributes[i]);
  
-@@ -303,37 +509,98 @@ GLuint CGLGetPixelFormatRetainCount(CGLPixelFormatObj pixelFormat) {
+@@ -303,37 +510,99 @@ GLuint CGLGetPixelFormatRetainCount(CGLPixelFormatObj pixelFormat) {
      return pixelFormat->retain_count;
  }
  
@@ -7227,6 +7228,7 @@ index ffd7fe054..f25fd9aa5 100644
 +    context->egl_config = contextConfig;
      context->egl_surface = NULL;
      context->swap_interval = 1;
++    context->swap_interval_requested = 0;
 +    context->native_present_surface=EGL_NO_SURFACE;
 +    context->native_present_context=EGL_NO_CONTEXT;
 +    context->native_present_target=NULL;
@@ -7267,7 +7269,7 @@ index ffd7fe054..f25fd9aa5 100644
      return context;
  }
  
-@@ -342,11 +609,17 @@ void CGLReleaseContext(CGLContextObj context) {
+@@ -342,11 +611,17 @@ void CGLReleaseContext(CGLContextObj context) {
          return;
      }
  
@@ -7288,7 +7290,7 @@ index ffd7fe054..f25fd9aa5 100644
  
      if (CGLGetCurrentContext() == context) {
          CGLSetCurrentContext(NULL);
-@@ -354,7 +627,11 @@ void CGLReleaseContext(CGLContextObj context) {
+@@ -354,7 +629,11 @@ void CGLReleaseContext(CGLContextObj context) {
  
      pthread_mutex_destroy(&(context->lock));
  
@@ -7301,12 +7303,9 @@ index ffd7fe054..f25fd9aa5 100644
  
      free(context);
  }
-@@ -383,9 +660,330 @@ CGLError CGLUnlockContext(CGLContextObj context) {
-     return kCGLNoError;
+@@ -384,8 +663,325 @@ CGLError CGLUnlockContext(CGLContextObj context) {
  }
  
-+static int swapIntervalRequested;
-+
  CGLError CGLFlushDrawable(CGLContextObj context) {
 -    eglSwapBuffers(display,context->egl_surface);
 -    return kCGLNoError;
@@ -7315,11 +7314,9 @@ index ffd7fe054..f25fd9aa5 100644
 +    /* darling-lol: EGL defaults to a swap interval of 1. When the window is covered or the compositor throttles it
 +     * (Xwayland answers about once a second), every swap blocks that long and the game's frame rate collapses to ~1 fps.
 +     * macOS apps get an unthrottled flush unless they ask for vsync through kCGLCPSwapInterval, which is handled in
-+     * CGLSetParameter; apply "no vsync" once per context here, while it is current. */
-+    static CGLContextObj swapIntervalContext;
-+    if (!swapIntervalRequested && context != swapIntervalContext && p_eglSwapInterval && CGLGetCurrentContext() == context) {
++     * CGLSetParameter; apply "no vsync" to unconfigured contexts while current. */
++    if (!context->swap_interval_requested && p_eglSwapInterval && CGLGetCurrentContext() == context) {
 +        p_eglSwapInterval(context->egl_display, 0);
-+        swapIntervalContext = context;
 +    }
 +    return p_eglSwapBuffers(context->egl_display, context->egl_surface) ? kCGLNoError : kCGLBadState;
 +}
@@ -7634,18 +7631,21 @@ index ffd7fe054..f25fd9aa5 100644
  }
  
  CGLError CGLSetParameter(CGLContextObj context, CGLContextParameter parameter, const GLint *value) {
-@@ -394,8 +992,9 @@ CGLError CGLSetParameter(CGLContextObj context, CGLContextParameter parameter, c
- 
+@@ -395,9 +991,11 @@ CGLError CGLSetParameter(CGLContextObj context, CGLContextParameter parameter, c
      if (parameter == kCGLCPSwapInterval)
      {
-+        swapIntervalRequested = 1;
          GLint v = *value;
 -        EGLBoolean success = eglSwapInterval(display, v);
+-        if (success)
 +        EGLBoolean success = p_eglSwapInterval(display, v);
-         if (success)
++        if (success) {
              context->swap_interval = v;
++            context->swap_interval_requested = 1;
++        }
          return success ? kCGLNoError : kCGLBadValue;
-@@ -417,14 +1016,19 @@ CGLError CGLGetParameter(CGLContextObj context, CGLContextParameter parameter, G
+     }
+     fprintf(stderr, "CGLSetParameter unimplemented for parameter %d\n", parameter);
+@@ -417,14 +1015,19 @@ CGLError CGLGetParameter(CGLContextObj context, CGLContextParameter parameter, G
      return kCGLNoError;
  }
  
diff --git a/tests/test_metal_vsync.py b/tests/test_metal_vsync.py
new file mode 100644
index 0000000..49bba1d
--- /dev/null
+++ b/tests/test_metal_vsync.py
@@ -0,0 +1,139 @@
+"""Exercise the patched presentation policy and CGL call order without a GPU."""
+from pathlib import Path
+import shutil
+import subprocess
+import tempfile
+import unittest
+import test_runtime_compatibility as sources
+
+
+@unittest.skipUnless(shutil.which('c++'), 'C++ compiler required')
+class MetalVSyncChecks(unittest.TestCase):
+    patched = sources.CompatibilityChecks.patched
+
+    def test_explicit_vsync_is_scoped_to_each_cgl_context(self):
+        source = self.patched('darling', 'src/frameworks/OpenGL/OpenGL.c')
+        methods = '\n'.join(sources.function(source, name) for name in ('CGLFlushDrawable', 'CGLSetParameter'))
+        fixture = r'''
+#include <cassert>
+#include <cstdio>
+using GLint=int;
+using CGLError=int;
+using CGLContextParameter=int;
+using EGLBoolean=int;
+constexpr int kCGLNoError=0, kCGLBadContext=1, kCGLBadState=2, kCGLBadAddress=3, kCGLBadValue=4;
+constexpr int kCGLCPSwapInterval=1;
+struct Context { int egl_display=1, egl_surface=1, swap_interval=1, swap_interval_requested=0; };
+using CGLContextObj=Context*;
+static Context* current;
+static int display=1, applied=-1;
+static bool fail=false;
+static int swapInterval(int, int value) { if(fail) return 0; applied=value; return 1; }
+static auto p_eglSwapInterval=swapInterval;
+static int p_eglSwapBuffers(int,int) { return 1; }
+static Context* CGLGetCurrentContext() { return current; }
+''' + methods + r'''
+int main() {
+    Context a, b;
+    current=&a;
+    int interval=1;
+    assert(CGLSetParameter(&a,kCGLCPSwapInterval,&interval)==0 && applied==1);
+    CGLFlushDrawable(&a); assert(applied==1);
+    current=&b;
+    CGLFlushDrawable(&b); assert(applied==0); // Another window retains its default.
+    current=&a;
+    interval=0;
+    assert(CGLSetParameter(&a,kCGLCPSwapInterval,&interval)==0 && applied==0);
+    interval=1;
+    assert(CGLSetParameter(&a,kCGLCPSwapInterval,&interval)==0 && applied==1);
+    current=&b; fail=true;
+    assert(CGLSetParameter(&b,kCGLCPSwapInterval,&interval)==kCGLBadValue);
+    assert(!b.swap_interval_requested); // Failed requests must not change policy.
+    fail=false; CGLFlushDrawable(&b); assert(applied==0);
+    assert(CGLFlushDrawable(nullptr)==kCGLBadContext);
+}
+'''
+        self.run_cpp(fixture)
+
+    def test_nested_layers_toggles_windows_and_context_failures(self):
+        source = self.patched('cocotron', 'QuartzCore/CALayerContext.m')
+        policy = sources.function(source, 'metalSwapInterval')
+        # Translate only Objective-C message/iteration syntax; compile the actual
+        # policy and flush body against inert layer and CGL fixtures.
+        policy = policy.replace('[[layer class] isSubclassOfClass: [CAMetalLayerInternal class]]', 'layer->metal')
+        policy = policy.replace('[(CAMetalLayer *)layer displaySyncEnabled]', 'layer->sync')
+        policy = policy.replace('for (CALayer *child in layer.sublayers)', 'for (CALayer *child : layer->children)')
+        flush = source.split('- (void) flush {', 1)[1].split('\n}\n', 1)[0]
+        fixture = r'''
+#include <cassert>
+#include <vector>
+using GLint = int;
+using CGLContextObj = int;
+constexpr int kCGLNoError = 0, kCGLCPSwapInterval = 1;
+constexpr int NULL_CONTEXT = 0;
+struct CALayer { bool metal=false, sync=true; std::vector<CALayer*> children; };
+struct Context { int interval=-2, swaps=0; } contexts[3];
+static int current=2, attached=0;
+static bool fail=false, skip=false;
+static int CGLGetCurrentContext() { return current; }
+static int CGLSetCurrentContext(int context) { current=context; return 0; }
+static int CGLContextMakeCurrentAndAttachToWindow(int context, int window) {
+    if(fail) return 1;
+    current=context; attached=window; return 0;
+}
+static int CGLSetParameter(int context, int parameter, const int* interval) {
+    assert(current==context && attached==context && parameter==kCGLCPSwapInterval);
+    contexts[context].interval=*interval; return 0;
+}
+static int CGLFlushDrawable(int context) {
+    assert(current==context && attached==context);
+    ++contexts[context].swaps; return 0;
+}
+static bool skipLocalRender(CALayer*, int) { return skip; }
+'''
+        fixture += policy
+        fixture += '\nstruct Window { int _glContext=1, _cglWindow=1, _frame=0; CALayer* _layer; void flush() {'
+        fixture += flush.replace('NULL', 'NULL_CONTEXT').replace('_frame.size', '_frame') + '\n} };\n'
+        fixture += r'''
+int main() {
+    CALayer root, container, metal, other;
+    metal.metal=other.metal=true;
+    root.children={&container}; container.children={&metal};
+    assert(metalSwapInterval(&root)==1);
+    Window a{1,1,0,&root};
+    a.flush(); assert(contexts[1].interval==1 && current==2);
+    metal.sync=false;
+    a.flush(); assert(contexts[1].interval==0 && current==2);
+    container.children.push_back(&other);
+    a.flush(); assert(contexts[1].interval==1);
+    other.sync=false;
+    a.flush(); assert(contexts[1].interval==0);
+    CALayer plain;
+    assert(metalSwapInterval(&plain)==-1);
+    Window b{2,2,0,&plain};
+    b.flush(); assert(contexts[2].interval==-2);
+    other.sync=true;
+    a.flush(); assert(contexts[1].interval==1 && contexts[2].interval==-2);
+    a._cglWindow=0;
+    int swaps=contexts[1].swaps;
+    a.flush(); assert(contexts[1].swaps==swaps);
+    a._cglWindow=1; fail=true;
+    a.flush(); assert(contexts[1].swaps==swaps && current==2);
+    fail=false; skip=true;
+    a.flush(); assert(contexts[1].swaps==swaps);
+    skip=false; current=0;
+    a.flush(); assert(current==0);
+    current=1; a.flush(); assert(current==1);
+    root.children.clear();
+    assert(metalSwapInterval(&root)==-1);
+}
+'''
+        self.run_cpp(fixture)
+
+    def run_cpp(self, fixture):
+        with tempfile.TemporaryDirectory() as directory:
+            path = Path(directory)
+            (path/'check.cpp').write_text(fixture)
+            result = subprocess.run(['c++', '-std=c++17', str(path/'check.cpp'), '-o', str(path/'check')], capture_output=True, text=True)
+            self.assertEqual(result.returncode, 0, result.stderr)
+            subprocess.run([str(path/'check')], check=True, timeout=10)
diff --git a/tests/test_x11_vrr.py b/tests/test_x11_vrr.py
new file mode 100644
index 0000000..267a995
--- /dev/null
+++ b/tests/test_x11_vrr.py
@@ -0,0 +1,164 @@
+"""Compile the patched VRR eligibility and drawable ownership methods with inert fixtures."""
+from pathlib import Path
+import shutil
+import subprocess
+import tempfile
+import unittest
+import test_runtime_compatibility as sources
+
+
+def body(source, signature):
+    return source.split(signature + ' {', 1)[1].split('\n}', 1)[0]
+
+
+@unittest.skipUnless(shutil.which('c++'), 'C++ compiler required')
+class VrrChecks(unittest.TestCase):
+    patched = sources.CompatibilityChecks.patched
+
+    def run_cpp(self, source):
+        with tempfile.TemporaryDirectory() as directory:
+            path = Path(directory)
+            (path/'check.cpp').write_text('#include <cstddef>\n' + source)
+            result = subprocess.run(['c++', '-std=c++17', str(path/'check.cpp'), '-o', str(path/'check')], capture_output=True, text=True)
+            self.assertEqual(result.returncode, 0, result.stderr)
+            subprocess.run([str(path/'check')], check=True, timeout=10)
+
+    def test_hints_only_allow_vrr_for_fullscreen_parent_presentation(self):
+        source = self.patched('cocotron', 'AppKit/X11.backend/X11Window.m')
+        method = body(source, '- (void) updateLayerPresentationHints: (BOOL) fullscreen')
+        getter = body(source, '- (void *) layerDrawableFor: (id) owner')
+        acquire = body(source, '- (void) acquireLayerDrawable: (id) owner').replace('[self updateLayerPresentationHints: _fullscreenRequested]', 'hints(_fullscreenRequested)')
+        release = body(source, '- (void) releaseLayerDrawable: (id) owner').replace('[self updateLayerPresentationHints: _fullscreenRequested]', 'hints(_fullscreenRequested)')
+        self.run_cpp(r'''
+#include <cassert>
+#include <cstring>
+using BOOL=bool;
+constexpr auto nil=nullptr;
+constexpr int False=0, XA_CARDINAL=6, PropModeReplace=0;
+static bool game=true;
+static int adaptive=-1,bypass=-1,calls=0;
+static bool X11IsLeagueGameWindow(int,int,int) { return game; }
+static const char* XInternAtom(int,const char* name,int) { return name; }
+static int XChangeProperty(int,int,const char* name,int type,int bits,int mode,unsigned char* data,int count) {
+    assert(type==XA_CARDINAL && bits==32 && mode==PropModeReplace && count==1);
+    int value=*(unsigned long*)data; ++calls;
+    if(!strcmp(name,"_VARIABLE_REFRESH")) adaptive=value;
+    else { assert(!strcmp(name,"_NET_WM_BYPASS_COMPOSITOR")); bypass=value; }
+    return 0;
+}
+struct Window {
+ int _display=1,_window=1,_delegate=1;
+ void* _layerDrawableOwner=nullptr;
+ void* _cglWindow=(void*)3; bool _hasAlpha=false,_fullscreenRequested=true;
+ void hints(BOOL fullscreen) {
+''' + method + '\n }\n void* drawable(void* owner) {' + getter + '\n}\n void acquire(void* owner) {' + acquire + '\n}\n void release(void* owner) {' + release + r'''
+ }
+};
+int main() {
+ Window w;
+ w.hints(true); assert(adaptive==0 && bypass==2);
+ w._layerDrawableOwner=&w;
+ w.hints(true); assert(adaptive==1 && bypass==0);
+ w.hints(false); assert(adaptive==0 && bypass==0);
+ w._layerDrawableOwner=nullptr;
+ w.hints(true); assert(adaptive==0 && bypass==2);
+ int before=calls; game=false; w.hints(true); assert(calls==before);
+ assert(!w.drawable(&w)); game=true;
+ int a,b;
+ assert(w.drawable(&a)==(void*)3);
+ w.acquire(&a); assert(w.drawable(&a)==(void*)3 && !w.drawable(&b));
+ w.acquire(&b); assert(w._layerDrawableOwner==&a);
+ w.release(&b); assert(w._layerDrawableOwner==&a);
+ w.release(&a); assert(!w._layerDrawableOwner && w.drawable(&b)==(void*)3);
+ w._hasAlpha=true; assert(!w.drawable(&a));
+}
+''')
+
+    def test_subwindows_borrow_only_when_visible_borderless_and_covering_parent(self):
+        source = self.patched('cocotron', 'AppKit/X11.backend/X11SubWindow.m')
+        method = body(source, '- (void *) sharedCGLWindow')
+        replacements = {'[_parent frame]':'_parent->frame', '[_parent styleMask]':'_parent->style',
+                        '[_parent layerDrawableFor: self]':'_parent->drawable(this)',
+                        '[_parent acquireLayerDrawable: self]':'_parent->acquire(this)',
+                        '[_parent releaseLayerDrawable: self]':'_parent->release(this)'}
+        for old,new in replacements.items():
+            method=method.replace(old,new)
+        self.run_cpp(r'''
+#include <cassert>
+using BOOL=bool;
+struct CGRect { struct {double x,y;} origin; struct {double width,height;} size; };
+static CGRect CGRectMake(double x,double y,double w,double h) {return {{x,y},{w,h}};}
+static bool CGRectEqualToRect(CGRect a,CGRect b) {return a.origin.x==b.origin.x && a.origin.y==b.origin.y && a.size.width==b.size.width && a.size.height==b.size.height;}
+constexpr int NSTitledWindowMask=1;
+static bool mapped;
+static void XMapWindow(int,int) {mapped=true;}
+static void XUnmapWindow(int,int) {mapped=false;}
+struct Parent {
+ CGRect frame=CGRectMake(0,0,800,600); int style=0; bool eligible=true;
+ void* owner=nullptr; void* surface=this;
+ void* drawable(void* requester) {return eligible && (!owner || owner==requester) ? surface : nullptr;}
+ void acquire(void* requester) {assert(!owner); owner=requester;}
+ void release(void* requester) {assert(owner==requester); owner=nullptr;}
+};
+struct Child {
+ Parent* _parent; CGRect _drawableFrame=CGRectMake(0,0,800,600);
+ BOOL _visible=true,_usingParentDrawable=false,_allowsParentDrawable=true; int _display=1,_window=2;
+ void* shared() {
+''' + method + r'''
+ }
+};
+int main() {
+ Parent p; Child a{&p}; Child b{&p};
+ assert(a.shared()==p.surface && !mapped && p.owner==&a);
+ assert(a.shared()==p.surface); // Repeated lookup does not reacquire.
+ assert(b.shared()==nullptr && mapped); // A second view cannot share ownership.
+ a._visible=false; assert(!a.shared() && !mapped && !p.owner);
+ a._visible=true; assert(a.shared()==p.surface);
+ a._drawableFrame.size.width=400;
+ assert(!a.shared() && mapped && !p.owner);
+ a._drawableFrame=CGRectMake(0,0,800,600); p.style=NSTitledWindowMask;
+ assert(!a.shared() && mapped);
+ p.style=0; p.eligible=false; assert(!a.shared() && mapped);
+ p.eligible=true; a._allowsParentDrawable=false; assert(!a.shared() && mapped);
+ a._allowsParentDrawable=true; a._drawableFrame.origin.x=1; assert(!a.shared() && mapped);
+ a._drawableFrame.origin.x=0; assert(a.shared()==p.surface && !mapped);
+}
+''')
+
+    def test_switching_surfaces_destroys_only_owned_child_drawables(self):
+        source = self.patched('cocotron', 'QuartzCore/CALayerContext.m')
+        method = body(source, '- (void) updateDrawable')
+        method=method.replace('[_subwindow setAllowsParentDrawable: hasMetalLayer(_layer)]', '_subwindow->allow(hasMetalLayer(_layer))')
+        method=method.replace('[_subwindow sharedCGLWindow]', '_subwindow->shared').replace('[_subwindow nativeWindow]', '_subwindow->native')
+        self.run_cpp(r'''
+#include <cassert>
+using BOOL=bool;
+using CGLContextObj=int;
+static int current=0,destroyed=0,created=0;
+static void* destroyedSurface;
+static int CGLGetCurrentContext() {return current;}
+static void CGLSetCurrentContext(int c) {current=c;}
+static void CGLDestroyWindow(void* surface) {assert(surface==(void*)10); destroyedSurface=surface; ++destroyed;}
+static void* CGLGetWindow(void*) {++created; return (void*)10;}
+static void CGLContextMakeCurrentAndAttachToWindow(int c,void*) {current=c;}
+static bool hasMetalLayer(int layer) {return layer!=0;}
+struct Subwindow {void* shared=nullptr; void* native=(void*)2; void allow(bool enabled) {assert(enabled);} };
+struct Context {
+ Subwindow* _subwindow; int _layer=1; int _glContext=1; void* _cglWindow=nullptr; bool _ownsCglWindow=false;
+ void update() {
+''' + method.replace('CGLSetCurrentContext(NULL)', 'CGLSetCurrentContext(0)') + r'''
+ }
+};
+int main() {
+ Subwindow sub; Context c{&sub};
+ c.update(); assert(created==1 && c._ownsCglWindow); // Ordinary clients still get a child.
+ c.update(); assert(created==1 && destroyed==0);
+ current=1; sub.shared=(void*)20;
+ c.update(); assert(destroyed==1 && destroyedSurface==(void*)10 && !c._ownsCglWindow && current==1);
+ c.update(); assert(destroyed==1);
+ sub.shared=(void*)30; c.update(); assert(destroyed==1 && c._cglWindow==(void*)30);
+ sub.shared=nullptr; c.update(); assert(created==2 && destroyed==1 && c._ownsCglWindow);
+ current=2; sub.shared=(void*)20; c.update(); assert(current==2 && destroyed==2);
+ c._subwindow=nullptr; c.update(); assert(destroyed==2);
+}
+''')
diff --git a/tools/build-riot-coregraphics-runtime.py b/tools/build-riot-coregraphics-runtime.py
index 8c5e72d..e00ff20 100644
--- a/tools/build-riot-coregraphics-runtime.py
+++ b/tools/build-riot-coregraphics-runtime.py
@@ -10,12 +10,13 @@ for line in (folder / 'CMakeFiles/CoreGraphics.dir/flags.make').read_text().spli
     if line.startswith('C_') and ' = ' in line:
         key, value = line.split(' = ', 1)
         flags[key] = shlex.split(value)
-obj = root / 'build/riot-CGDirectDisplay.o'
-subprocess.run(['clang', *flags['C_DEFINES'], *flags['C_INCLUDES'], *flags['C_FLAGS'],
-                '-O2', '-Wno-macro-redefined', '-c',
-                str(root / 'build/darling-src/src/external/cocotron/CoreGraphics/CGDirectDisplay.m'),
-                '-o', str(obj)], check=True)
 link = shlex.split((folder / 'CMakeFiles/CoreGraphics.dir/link.txt').read_text())
-link[link.index('CMakeFiles/CoreGraphics.dir/CGDirectDisplay.m.o')] = str(obj)
+for name in ('CGDirectDisplay', 'CGSubWindow'):
+    obj = root / f'build/riot-{name}.o'
+    subprocess.run(['clang', *flags['C_DEFINES'], *flags['C_INCLUDES'], *flags['C_FLAGS'],
+                    '-O2', '-Wno-macro-redefined', '-c',
+                    str(root / f'build/darling-src/src/external/cocotron/CoreGraphics/{name}.m'),
+                    '-o', str(obj)], check=True)
+    link[link.index(f'CMakeFiles/CoreGraphics.dir/{name}.m.o')] = str(obj)
 link[link.index('-o') + 1] = str(root / 'build/riot-CoreGraphics')
 subprocess.run(link, cwd=folder, check=True)
diff --git a/tools/build-riot-x11-runtime.py b/tools/build-riot-x11-runtime.py
index 192d9f3..9c3d173 100644
--- a/tools/build-riot-x11-runtime.py
+++ b/tools/build-riot-x11-runtime.py
@@ -14,7 +14,7 @@ for line in (framework / 'CMakeFiles/X11_backend.dir/flags.make').read_text().sp
         key, value = line.split(' = ', 1)
         flags[key] = shlex.split(value)
 link = shlex.split((framework / 'CMakeFiles/X11_backend.dir/link.txt').read_text())
-for name in ('X11Display', 'X11Window'):
+for name in ('X11Display', 'X11Window', 'X11SubWindow'):
     obj = project / f'build/riot-{name}.o'
     subprocess.run(['clang', *flags['C_DEFINES'], *flags['C_INCLUDES'], *flags['C_FLAGS'], '-O3', '-march=native', '-mtune=generic', '-Wno-macro-redefined', '-c', str(project / f'build/darling-src/src/external/cocotron/AppKit/X11.backend/{name}.m'), '-o', str(obj)], check=True)
     link[link.index(f'CMakeFiles/X11_backend.dir/X11.backend/{name}.m.o')] = str(obj)
diff --git a/tools/riot-metal-presentation-check.mm b/tools/riot-metal-presentation-check.mm
index 5266d8d..65f281f 100644
--- a/tools/riot-metal-presentation-check.mm
+++ b/tools/riot-metal-presentation-check.mm
@@ -8,6 +8,14 @@
 #import <OpenGL/gl.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <unistd.h>
+extern "C" void _dispatch_main_queue_callback_4CF(void *);
+
+@interface PresentationCheckWindow : NSWindow
+@end
+@implementation PresentationCheckWindow
+- (BOOL)canBecomeKeyWindow { return YES; }
+@end
 
 static void verifyPresentation(bool value, const char* message) {
     if (!value) { fprintf(stderr, "FAIL: %s\n", message); exit(1); }
@@ -18,7 +26,12 @@ static void pump(NSApplication* app) {
         NSEvent* event = [app nextEventMatchingMask:NSAnyEventMask untilDate:[NSDate distantPast]
                                             inMode:NSDefaultRunLoopMode dequeue:YES];
         if (event) [app sendEvent:event];
-        [[NSRunLoop currentRunLoop] runUntilDate:[NSDate dateWithTimeIntervalSinceNow:0.005]];
+        // A timed NSRunLoop wait can miss its deadline on Darling when the
+        // X connection is quiet. Parent presentation no longer supplies child
+        // Expose events to wake it; service sources without a blocking wait.
+        CFRunLoopRunInMode(kCFRunLoopDefaultMode, 0.0, true);
+        _dispatch_main_queue_callback_4CF(nullptr);
+        usleep(1000);
     }
 }
 int main() {
@@ -35,6 +48,7 @@ int main() {
         id<MTLDevice> device = MTLCreateSystemDefaultDevice();
         verifyPresentation(device != nil, "device");
         CAMetalLayer* layer = [CAMetalLayer layer];
+        verifyPresentation(layer.displaySyncEnabled == YES, "VSync enabled by default");
         layer.device = device;
         layer.drawableSize = CGSizeMake(160,96);
         layer.frame = CGRectMake(0,0,160,96);
@@ -52,12 +66,17 @@ int main() {
         } else {
             view.layer = layer;
         }
-        NSWindow* window = [[NSWindow alloc] initWithContentRect:NSMakeRect(50,50,160,96)
-          styleMask:NSTitledWindowMask backing:NSBackingStoreBuffered defer:NO];
-        window.title = @"Metal presentation check";
+        const bool parentDrawable = getenv("RIOT_PRESENTATION_PARENT") != nullptr;
+        NSWindow* window = [[PresentationCheckWindow alloc] initWithContentRect:NSMakeRect(50,50,160,96)
+          styleMask:(parentDrawable ? NSBorderlessWindowMask : NSTitledWindowMask) backing:NSBackingStoreBuffered defer:parentDrawable];
+        window.title = parentDrawable ? @"Presentation (TM) Client" : @"Metal presentation check";
         window.contentView = view;
         [window makeKeyAndOrderFront:nil];
         pump(app);
+        if (parentDrawable) {
+            void *borrowed = [[(CALayerContext*)[layer _context] subwindow] sharedCGLWindow];
+            verifyPresentation(borrowed != nullptr, "full-window game layer borrows managed parent drawable");
+        }
         id<MTLCommandQueue> queue = [device newCommandQueue];
         const unsigned frameCount = captureTest ? 130u : getenv("RIOT_PRESENTATION_STRESS") ? 120u : 10u;
         for (unsigned frame = 0; frame < frameCount; ++frame) {
@@ -66,6 +85,7 @@ int main() {
                 verifyPresentation(flag != nullptr, "request second bounded capture");
                 fclose(flag);
             }
+            layer.displaySyncEnabled = (frame % 3) != 1;
             @autoreleasepool {
                 id<CAMetalDrawable> drawable = [layer nextDrawable];
                 verifyPresentation(drawable != nil, "drawable after late window/context attachment");
@@ -82,6 +102,23 @@ int main() {
                 [commands commit];
                 [commands waitUntilCompleted];
                 pump(app);
+                GLint interval = -1;
+                CGLGetParameter([(CALayerContext*)[layer _context] glContext], kCGLCPSwapInterval, &interval);
+                verifyPresentation(interval == (layer.displaySyncEnabled ? 1 : 0), "Metal VSync reaches window swap interval");
+                if (parentDrawable) {
+                    void *borrowed = [[(CALayerContext*)[layer _context] subwindow] sharedCGLWindow];
+                    verifyPresentation(borrowed != nullptr, "parent drawable remains borrowed");
+                    if (frame == 3 && getenv("RIOT_PRESENTATION_RESIZE")) {
+                        CALayerContext* context = (CALayerContext*)[layer _context];
+                        CGRect original = [view frame];
+                        [context setFrame:CGRectMake(0,0,original.size.width / 2,original.size.height)];
+                        [context render]; [context flush];
+                        verifyPresentation([[context subwindow] sharedCGLWindow] == nullptr, "partial view falls back to child drawable");
+                        [context setFrame:original];
+                        [context render]; [context flush];
+                        verifyPresentation([[context subwindow] sharedCGLWindow] != nullptr, "restored view borrows parent drawable again");
+                    }
+                }
             }
         }
         CGLContextObj previous = CGLGetCurrentContext();
diff --git a/upstream/manifest.json b/upstream/manifest.json
index 1dd1cac..60fbbb8 100644
--- a/upstream/manifest.json
+++ b/upstream/manifest.json
@@ -57,7 +57,7 @@
       "revision": "c8d38d16a9f613d300157bebbab2b9501bc0c274",
       "repository": "https://github.com/darlinghq/darling-cocotron.git",
       "patch": "patches/cocotron.patch",
-      "modified_files": 104,
+      "modified_files": 115,
       "new_files": [
         "QuartzCore/include/QuartzCore/CATransformLayer.h",
         "AppKit/NSGeometryTrace.h"