Mac in the headset: measure every frame, adapt to the network, separate windows

- Per-frame timing on the Mac's clock (capture, encode, network, decode,
  draw), viewer clock sync and reports, input echo, /stats and a HUD.
- scripts/macview-bench.py: repeatable runs on the real Frame, a shaping
  relay (no sudo), interleaved A/B between agent settings; results in
  bench/results/.
- Adaptive controller: ack-based send gate with jitter-aware slack, AIMD
  bitrate that knows when a stream is app-limited, fps then size tiers.
  On a 50->3->50 Mbit/s step, scroll p95 went from 4.7 s to 72 ms; no cost
  on a clean link.
- Separate mode: real AppKit event loop (HiDPI and NSScreen now work),
  cropped capture for fixed-size windows, windows kept on their display,
  graceful quit restores windows; stop/start races fixed.
- Encoder timeline clamp (no oversized frame after a pause).
- Frame Control shows each live stream's fps, delay, bitrate and tier.

Reviewed by GPT-6 Astra xhigh (read-only), 7 rounds; findings fixed.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

mac/frame-mac-view/Sources/CGVirtualDisplay.h

@@ -0,0 +1,28 @@
+// Private CoreGraphics classes for virtual displays (as used by DeskPad,
+// BetterDisplay and quest-display). Not in any SDK; see
+// docs/mac-window-separation.md.
+#import <Foundation/Foundation.h>
+#import <CoreGraphics/CoreGraphics.h>
+@interface CGVirtualDisplayDescriptor : NSObject
+@property (retain, nonatomic) dispatch_queue_t queue;
+@property (retain, nonatomic) NSString *name;
+@property (nonatomic) unsigned int maxPixelsHigh;
+@property (nonatomic) unsigned int maxPixelsWide;
+@property (nonatomic) CGSize sizeInMillimeters;
+@property (nonatomic) unsigned int serialNum;
+@property (nonatomic) unsigned int productID;
+@property (nonatomic) unsigned int vendorID;
+@property (copy, nonatomic) void (^terminationHandler)(id, id);
+@end
+@interface CGVirtualDisplayMode : NSObject
+- (instancetype)initWithWidth:(unsigned int)width height:(unsigned int)height refreshRate:(double)refreshRate;
+@end
+@interface CGVirtualDisplaySettings : NSObject
+@property (retain, nonatomic) NSArray *modes;
+@property (nonatomic) unsigned int hiDPI;
+@end
+@interface CGVirtualDisplay : NSObject
+@property (readonly, nonatomic) unsigned int displayID;
+- (instancetype)initWithDescriptor:(CGVirtualDisplayDescriptor *)descriptor;
+- (BOOL)applySettings:(CGVirtualDisplaySettings *)settings;
+@end