Add AGENTS.md for Cursor Cloud development environment setup

AGENTS.md

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+# AGENTS.md
+
+## Cursor Cloud specific instructions
+
+This is the **mParticle Dotnet Server Events SDK** — a .NET library for sending event data to the mParticle platform via their server-side Events API.
+
+### Project structure
+
+- `src/mParticle.Sdk/` — SDK library (targets `netstandard2.1`)
+- `src/mParticle.Sdk.Test/` — xUnit test project (targets `net6.0`)
+- `mParticle.sln` — Visual Studio solution file
+
+### Prerequisites
+
+.NET 6.0 SDK is required. It is installed to `$HOME/.dotnet` with `DOTNET_ROOT` and `PATH` configured in `~/.bashrc`.
+
+### Key commands
+
+See `.github/workflows/test.yml` for the CI commands. Summary:
+
+- **Restore:** `dotnet restore`
+- **Build:** `dotnet build --configuration Release --no-restore`
+- **Test:** `dotnet test --no-restore --verbosity normal`
+
+All 642 unit tests use dummy API credentials and do not require a live mParticle API connection. Some tests make HTTP calls that return `Forbidden` — this is expected and tests still pass.
+
+### Caveats
+
+- No linter is configured in this repo (no `.editorconfig` enforcement, no `dotnet format` in CI). The CI only runs build + test.
+- No Docker, database, or external service dependencies.
+- The `bump-version.sh` script is for release version management, not for development setup.