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+# Android Vulkan Extension Survey
+
+Pre-Lume-Pad reference. Lists every Vulkan device extension the runtime
++ test app request at session bring-up, and predicts what's present on
+the emulator (swiftshader-via-gfxstream) vs Lume Pad's Adreno GPU.
+
+The point: when you plug in Lume Pad and run `scripts/android-smoketest.sh`,
+**you should know in advance which `xrCreate*` step is expected to advance
+past the emulator wall and which steps will be the first to touch
+hardware-specific behavior**. If anything else fails, that's a bug worth
+investigating.
+
+## Lume Pad 2 GPU baseline
+
+| | |
+|---|---|
+| SoC | Snapdragon 845 (Adreno 630, Lume Pad 1) or 888 (Adreno 660, Lume Pad 2) |
+| Vulkan driver | Qualcomm Adreno Vulkan ICD (system, signed) |
+| Vulkan API version | 1.1 minimum, 1.3 typical for Adreno 660+ |
+| Source of truth | `vulkan.gpuinfo.org` reports for the exact device model |
+
+## Required device extensions (xrCreateVulkanDeviceKHR side)
+
+The runtime appends these to whatever the test app already requests.
+Source: `src/xrt/state_trackers/oxr/oxr_vulkan.c::required_vk_device_extensions[]`
+on Android (`XRT_GRAPHICS_BUFFER_HANDLE_IS_AHARDWAREBUFFER` +
+`XRT_GRAPHICS_SYNC_HANDLE_IS_FD`).
+
+| # | Extension | Adreno 6xx/7xx | Emulator (swiftshader) | Notes |
+|---|---|:---:|:---:|---|
+| 1 | `VK_KHR_dedicated_allocation` | ✅ | ✅ | Core in 1.1 |
+| 2 | `VK_KHR_external_fence` | ✅ | ✅ | Core in 1.1 |
+| 3 | `VK_KHR_external_memory` | ✅ | ✅ | Core in 1.1 |
+| 4 | `VK_KHR_external_semaphore` | ✅ | ✅ | Core in 1.1 |
+| 5 | `VK_KHR_get_memory_requirements2` | ✅ | ✅ | Core in 1.1 |
+| 6 | `VK_ANDROID_external_memory_android_hardware_buffer` | ✅ | ❌ | Android-only. **First likely emulator-wall** |
+| 7 | `VK_KHR_sampler_ycbcr_conversion` | ✅ | ⚠️ | Required by #6; transitively missing on emulator |
+| 8 | `VK_KHR_maintenance1` | ✅ | ✅ | Core in 1.1 |
+| 9 | `VK_KHR_bind_memory2` | ✅ | ✅ | Core in 1.1 |
+| 10 | `VK_EXT_queue_family_foreign` | ✅ | ❌ | Required by #6; tied to AHardwareBuffer |
+
+**Emulator failure mode (today, captured 2026-05-27):** at session bring-up,
+`null_compositor_create_system_with_dims` calls `vk_create_device` and gets
+`VK_ERROR_EXTENSION_NOT_PRESENT`. The runtime gracefully degrades and lets
+`xrCreateInstance` succeed (sentinel fires). The test app's own
+`xrCreateVulkanDeviceKHR` then fails with the same error a few calls later
+once it tries to enable an extension swiftshader doesn't have. Both fails
+are the same root cause: **extensions #6/#7/#10 are AHardwareBuffer-related
+and swiftshader doesn't implement them.**
+
+**Lume Pad prediction:** all 10 required extensions present. Both
+`null_compositor`'s VK device AND the test app's VK device should succeed.
+
+## Optional device extensions (silently skipped if missing)
+
+Source: `src/xrt/state_trackers/oxr/oxr_vulkan.c::optional_device_extensions[]`
+on Android.
+
+| Extension | Adreno 6xx/7xx | Emulator | Notes |
+|---|:---:|:---:|---|
+| `VK_KHR_external_semaphore_fd` | ✅ | ✅ | Used for cross-process sync |
+| `VK_KHR_external_fence_fd` | ✅ | ✅ | Used for cross-process sync |
+| `VK_KHR_image_format_list` | ✅ | ✅ | Swapchain image format optimisation |
+| `VK_KHR_timeline_semaphore` | ✅ | ⚠️ | Adreno added in 2020 drivers; older devices may miss |
+
+## Null compositor's separate VK device
+
+The runtime's null compositor builds its own VkDevice (the "internal"
+device, separate from the app-facing one). Same list as above plus
+`VK_KHR_swapchain` (line 90 of `null_compositor.c`). On Android the null
+compositor doesn't need a present surface, so swapchain is harmless if
+present but **its absence won't break headless operation** (only the
+internal device init logs a WARN and the runtime falls through to the
+fallback path).
+
+## CNSDK plug-in's VK requirements
+
+The CNSDK plug-in does NOT create its own VkDevice — it uses the device
+the runtime hands it via the DP `create_dp_vk` factory. So all CNSDK VK
+calls go through the test-app-created device, which already has the full
+required-extension set above.
+
+CNSDK's `leia_interlacer_vulkan_initialize` will fail at runtime if the
+device is missing any of the extensions CNSDK uses internally. The CNSDK
+0.7.28 source isn't fully transparent on this; check the published
+`vulkaninfo` for Adreno 6xx and confirm at first session if the
+interlacer errors out.
+
+## Step-by-step expectation at first Lume Pad bring-up
+
+Walk through these in order — the column heading is what should appear
+in logcat at each milestone.
+
+| Step | Log line | Emulator | Lume Pad expected |
+|---|---|:---:|:---:|
+| Loader init | `xrInitializeLoaderKHR -> XR_SUCCESS` | ✅ | ✅ |
+| Broker resolves runtime | `OpenXR-Loader: Got runtime: package: …` | ✅ | ✅ |
+| Plug-in dlopen | `plugin loader: active plug-in: id=leia-cnsdk …` | ✅ | ✅ |
+| **Null compositor VK device** | `monado.create_device: VK_ERROR_EXTENSION_NOT_PRESENT` | ❌ (expected) | ✅ (no error log) |
+| Instance creation | `ANDROID_POC_SENTINEL xrCreateInstance=XR_SUCCESS` | ✅ | ✅ |
+| `xrGetSystem` | `System: "DisplayXR: Leia CNSDK (Android)"` | ✅ | ✅ |
+| `xrGetVulkanGraphicsRequirements2KHR` | `Vulkan API: min=1.0.0 max=…` | ✅ | ✅ |
+| `xrCreateVulkanInstanceKHR` | `xrCreateVulkanInstanceKHR -> XR_SUCCESS` | ✅ | ✅ |
+| `xrGetVulkanGraphicsDevice2KHR` | `xrGetVulkanGraphicsDevice2KHR -> XR_SUCCESS` | ✅ | ✅ |
+| **`xrCreateVulkanDeviceKHR`** | `xrCreateVulkanDeviceKHR -> XR_SUCCESS` (no `vk_result=-7`) | ❌ vk_result=-7 (expected) | ✅ first-touch hardware step |
+| `xrCreateSession` | `xrBeginSession returned XR_SUCCESS` | (unreached) | ✅ |
+| `leia_interlacer_vulkan_initialize` | DP creation log | (unreached) | ✅ if all CNSDK-needed exts present |
+| First frame | `Atlas blit: view_count=2, hardware_3d=1` | (unreached) | ✅ |
+
+## What to grep for if Lume Pad fails
+
+```bash
+# Which extension exactly is missing (Adreno driver will spell it out):
+adb logcat | grep -i 'extension not found\|extension not supported\|VK_ERROR_EXTENSION_NOT_PRESENT'
+
+# What Adreno actually reports:
+adb logcat | grep -i 'vulkan' | grep -i 'apiVersion\|driverName\|deviceName'
+
+# All Vulkan-related WARN+ERROR from the runtime:
+adb logcat | grep -E 'monado\.(create_device|vk_|comp_)' | grep -E 'ERROR|WARN'
+```
+
+## How to update this doc
+
+If Lume Pad reveals an extension we got wrong here:
+
+1. Capture the exact error: `adb logcat | grep -A2 VK_ERROR_EXTENSION_NOT_PRESENT`
+2. Look up the device's actual extension list at `vulkan.gpuinfo.org`.
+3. Update the matching row's "Adreno" column with ❌ + a note on which Adreno gen lost support.
+4. If the runtime needs to make the extension optional, change it in `src/xrt/state_trackers/oxr/oxr_vulkan.c` (move from `required_vk_device_extensions[]` to `optional_device_extensions[]`).