Android: setprop-tunable calibration knobs (face axes + UV flip)

[leaiss]

Summary

Stacked on #14 (bundle-transitive). Wires the symptom→fix table in docs/cnsdk-android-calibration.md into runtime debug.dxr.leia.* system properties so post-Lume-Pad calibration iteration doesn't need a rebuild + reinstall + relaunch cycle — just `setprop` + `am force-stop` + restart.

Knobs

Property	Default	Effect
`debug.dxr.leia.flip_uv`	1	Pass false to leia_interlacer_set_flip_input_uv_vertical
`debug.dxr.leia.face_flip_x`	0	Negate out_x
`debug.dxr.leia.face_flip_y`	0	Negate out_y
`debug.dxr.leia.face_flip_z`	0	Negate out_z
`debug.dxr.leia.face_swap_xy`	0	Swap out_x ↔ out_y (before flips)

Tile-to-eye swap (B17) intentionally out of scope — the current atlas mode has no CNSDK-side swap parameter; that needs a runtime-side atlas blit change.

Implementation notes

• Values cached at first plug-in call (std::atomic<bool> g_calib_loaded). Re-reading mid-session would race in-flight frames, and __system_property_get isn't free per-frame.
• Logged once via U_LOG_W at first read so values land in logcat at every session start — visible even when CNSDK init never completes (e.g. emulator).
• Hooked from leia_plugin_android_probe() (runs at xrCreateInstance time) via new C-callable leia_cnsdk_log_calibration_knobs(), so emulator validation can confirm the plumbing even though CNSDK init can't complete there.

Verification

Run `scripts/android-smoketest.sh` from the runtime repo (validated against the new plug-in build):

```

Defaults:

W monado.ensure_calibration_loaded: HW_DBG_CNSDK calibration: flip_uv=1 face_flip_xyz=000 face_swap_xy=0

After: adb shell setprop debug.dxr.leia.{flip_uv 0,face_flip_x 1,face_swap_xy 1}

+ adb shell am force-stop ...

+ adb shell am start ...

W monado.ensure_calibration_loaded: HW_DBG_CNSDK calibration: flip_uv=0 face_flip_xyz=100 face_swap_xy=1
```

Why

Without this, every calibration iteration on Lume Pad costs:

1. Edit constant in `leia_cnsdk.cpp`
2. Rebuild plug-in (~30s)
3. `install-runtime-jnilibs` (~5s)
4. Rebuild runtime APK (~2m)
5. Adb install (~10s)
6. Relaunch + test

≈ 3 minutes per flip. With 5 binary knobs there are 32 combinations to potentially test; this collapses to 5 seconds per knob via setprop.

Stacking

Based on plug-in #14. Rebase onto main once #14 lands.

🤖 Generated with Claude Code