Document minimum Android API 28 in README and CLAUDE.md

posix_spawn* (used by mtmd-helper.cpp via subprocess.h) is only declared
in NDK headers when __ANDROID_API__ >= 28, making Android 9.0 Pie the
minimum supported version. Add an explicit note to the README [!NOTE]
block, the "Importing in Android" section, and a new CLAUDE.md section
that mirrors the CUDA version pattern with upgrade instructions.

https://claude.ai/code/session_01RcJfwgM2cfjd3n5A8JrGqe

Author: claude

CLAUDE.md

@@ -38,6 +38,20 @@ git add .github/build_cuda_linux.sh pom.xml CLAUDE.md
 git commit -m "Upgrade CUDA from 13.2 to 13.3"
 ```
 
+## Android minimum API level
+
+Current Android minimum API level: **28** (Android 9.0 Pie)
+
+To change the minimum API level, update the following **three** places:
+
+1. **`CMakeLists.txt`** — the `add_compile_definitions(__ANDROID_API__=28)` line (controls which NDK header symbols are exposed).
+2. **`.github/workflows/publish.yml`** — `-DANDROID_PLATFORM=android-28` in both the `crosscompile-android-aarch64` and `crosscompile-android-aarch64-opencl` job steps.
+3. **`CLAUDE.md`** (this file) — the "Current Android minimum API level" line above and the `-DANDROID_PLATFORM` values in the local sanity-build examples.
+
+Also update the minimum-API note in **`README.md`** (the `[!NOTE]` block near the Android classifier entries and the "Importing in Android" section).
+
+**Why API 28?** `mtmd-helper.cpp` (part of the upstream llama.cpp `mtmd` multimodal library) includes `vendor/sheredom/subprocess.h`, which calls `posix_spawn`, `posix_spawnp`, and `posix_spawn_file_actions_*`. The Android NDK headers only expose those declarations when `__ANDROID_API__ >= 28`. The symbols exist in `libc.so` at all API levels; the define only gates their header visibility.
+
 ## OpenCL / Adreno backend on Android
 
 A second Android arm64 artifact is built with the OpenCL backend enabled and

README.md

@@ -202,6 +202,9 @@ Pick at most one — they are mutually exclusive.
 > by the released artifacts; building from source via the
 > `.github/dockcross/dockcross-android-arm` toolchain is possible but not
 > wired into CI.
+>
+> The minimum required Android version is **API 28 (Android 9.0 Pie)**.
+> Devices running Android 8.1 (API 27) or earlier are not supported.
 
 ### Setup required
 
@@ -506,6 +509,10 @@ The `LogLevel` enum values passed to the callback correspond to the native llama
 
 ## Importing in Android
 
+> [!IMPORTANT]
+> **Minimum Android version: API 28 (Android 9.0 Pie).** Devices running
+> Android 8.1 (API 27) or earlier are not supported.
+
 You can use this library in Android project.
 1. Add java-llama.cpp as a submodule in your an droid `app` project directory
 ```shell