Fix spatial mode on macOS Tahoe + remove gyro yaw drift

[alexiscrocilla]

Three independent fixes for issues reported by users (spatial mode invisible on macOS Tahoe + chronic gyro drift). Split across three commits so each can be reviewed and reverted independently if needed.

1. fix(spatial): route output window to glasses on macOS Tahoe

The borderless NSWindow used for spatial output was failing to display on the XReal Air on macOS 26 Tahoe in two ways:

• canBecomeKeyWindow defaults to false for borderless windows. On Tahoe this stops MTKView's display link from delivering active draw callbacks — the first frame renders then the renderer idles, panel goes black.
• .screenSaver window level was demoted by the Tahoe window server, so a window at negative Cocoa coordinates (where the XReal Air sits in a typical desk arrangement) gets clamped onto the built-in display as a thin strip.

Fix: subclass NSWindow as KeyableBorderlessWindow (override canBecomeKey/canBecomeMain → true), raise window level to CGShieldingWindowLevel + 1, and call setFrame(_:display:) after orderFront(_:) to defeat Tahoe's post-creation clamp.

2. fix(imu): apply factory calibration from glasses flash to remove gyro drift

device_imu_open already streams the per-unit calibration JSON blob from on-device flash via the GET_CAL_DATA_LENGTH (0x14) / CAL_DATA_GET_NEXT_SEGMENT (0x15) HID message pair, but the bytes were being discarded with the comment "json-c calibration helpers removed". As a result, every unit fell back to identity calibration, leaving ~1°/s of residual gyro yaw bias — the visible head-locked drift users report.

Fix: accumulate the streamed segments into a malloc'd buffer (1 MiB sanity cap), parse with a small hand-rolled string-scanner (~140 LOC, no new dependencies) targeting only the ~10 keys we consume, and populate device->calibration. apply_calibration() already handles unit conversion (rad/s → deg/s for gyro, m/s² → g for accel), so no math changes downstream. Falls back silently to identity if parsing fails — never worse than before.

For empirical verification of the on-wire JSON format, set ULTRAXREAL_DUMP_CAL=/path/to/cal.json before launch and the raw blob is dumped on success.

3. feat(spatial): cursor warp on activation + grey fallback for empty canvas

Two UX improvements:

• Cursor warp. Spatial mode unmirrors the XReal Air and takes the panel directly, so the OS cursor stays on the built-in display where the user can't see it. Auto-warp it onto the centre of the virtual display when spatial activates, and expose ⌘⇧M / "Move Cursor to Virtual Display" in the menu so it can be re-invoked if the user clicks back to the built-in display.
• Grey clearColor when no real frame yet. SCK delivers status-only sample buffers (.idle/.blank/.suspended) when the captured content isn't changing. An empty virtual display produces only those, so the renderer used to early-return on every callback and MTKView never painted — solid black on the glasses, indistinguishable from a broken renderer. Now: skip non-.complete buffers, and when no real frame has arrived yet, render a dark-grey (#1a1a1a) clear pass so the user knows the renderer is alive and the canvas is just empty.

Testing

• M4 MacBook Pro 14" 2024 / macOS Tahoe 26.2 (25C56) / XReal Air gen 1
• Spatial mode appears on glasses immediately on activation
• 30s head-still test shows no visible drift (was ~10° before the calibration fix)
• Static (ultrawide) mode unaffected

Caveats

• The calibration JSON parser heuristic-matches key names (acc/accelerometer, bias/offset, scale/sensitivity, misalignment/alignment). If XReal ever changes their JSON schema we may need to add variants — the ULTRAXREAL_DUMP_CAL env var helps diagnose this.
• A note in the README about needing to refresh the Screen Recording TCC toggle after upgrading the app would help — SCStream.startCapture() silently fails with -3801 if the new cdhash doesn't match the cached permission. Happy to add this in a follow-up PR if you prefer.