Set up Cursor Cloud dev environment

AGENTS.md

@@ -0,0 +1,51 @@
+# AGENTS.md
+
+## Cursor Cloud specific instructions
+
+`fvp` is a **Flutter plugin** (a `video_player` implementation + backend player API) backed by
+the native `libmdk`/`mdk-sdk` C/C++ SDK via Dart FFI. There is **no backend server, database, or
+listening port** — "running" the product means running the demo app in `example/`.
+
+### Environment already provisioned (by the startup update script + one-off setup)
+- Flutter SDK (stable) is installed at `/opt/flutter` and symlinked onto `PATH` via
+  `/usr/local/bin/flutter` and `/usr/local/bin/dart`, so `flutter`/`dart` work in any shell
+  (no PATH export needed). Linux desktop is enabled (`flutter config --enable-linux-desktop`).
+- Linux native build toolchain is installed: `cmake`, `clang`, `ninja-build`, `pkg-config`,
+  `libgtk-3-dev`, `libpulse-dev`. Note `libstdc++-14-dev` is required (not just `-13`): clang 18
+  selects the GCC 14 toolchain, and without `libstdc++-14-dev` the C++ link step fails with
+  `cannot find -lstdc++`.
+- The update script runs `flutter pub get` for the plugin and `example/`.
+
+### Running / building the example app (dev mode)
+Run from `example/` with an X display (the VM provides `DISPLAY=:1`):
+```
+cd example
+DISPLAY=:1 flutter run -d linux      # dev mode (hot reload)
+flutter build linux --debug          # build only
+```
+Standard test/lint commands (see `.github/workflows/build.yml`):
+```
+flutter analyze          # lint (run from repo root)
+cd example && flutter test
+```
+
+### Non-obvious gotchas
+- **First native build downloads `mdk-sdk`**: on the first `flutter build/run linux`, `cmake/deps.cmake`
+  downloads the native SDK archive from SourceForge (needs outbound network). It is cached under
+  `example/linux/flutter/ephemeral/.../mdk-sdk` afterward. Use `FVP_DEPS_URL` + `FVP_DEPS_SHA256`
+  (or `FVP_DEPS_LATEST=1`) to pin/override the SDK source.
+- **Never reuse a broken CMake cache**: the Flutter Linux `CMakeLists.txt` only forces
+  `CMAKE_INSTALL_PREFIX` to the bundle dir when `CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT` is
+  true (i.e. the *first* configure). If a first configure fails partway (e.g. missing toolchain)
+  and you fix the toolchain and re-run, the stale cache keeps `CMAKE_INSTALL_PREFIX=/usr/local` and
+  the build fails with `Permission denied` copying to `/usr/local/fvp_example`. Fix: delete
+  `example/build/linux` and rebuild clean.
+- **Harmless runtime warnings** on this headless-GPU VM: `libEGL warning: DRI3 error`,
+  `Failed to open VDPAU backend libvdpau_nvidia.so`, and `Unable to access driver information using
+  'eglinfo'` in `flutter doctor`. Rendering falls back to software and video still plays.
+- **Android toolchain is not installed** (`flutter doctor` shows Android as missing). Only the
+  Linux desktop / web targets are set up here.
+- **Pre-existing stale test**: `example/test/player_test.dart` fails on a clean checkout — it
+  expects `VideoPlayerPlatform.instance` to be `MdkVideoPlayer`, but the registered instance is
+  `MdkVideoPlayerPlatform` (and `MdkVideoPlayer` extends `mdk.Player`, not `VideoPlayerPlatform`).
+  This is a bug in the test, unrelated to environment setup.