docs: 增加 AGENTS.md

AGENTS.md

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+# AGENTS.md
+
+C# source loader for the Hosihikari Framework. It compiles `.cs` files with Roslyn at load and runs
+the result in a collectible assembly load context.
+
+## Repository map
+
+- `src/` — loader implementation and cache.
+- `host/` — assertion host for compilation, caching, isolation, and unload.
+- `test/` — fixture packages and private dependencies.
+- `pack.ps1` — build the `hosihikari-csharp` lip package.
+- `tooth.json` — lip package metadata.
+
+## Build and verify
+
+```bash
+dotnet run --project host/Hosihikari.PluginLoader.CSharp.Host.csproj -c Release --nologo
+pwsh ./pack.ps1 -Version 1.0.0 -OutputRoot artifacts
+```
+
+The host expects sibling `PluginManager`, `Plugin.Abstractions`, and
+`Hosihikari.McMaster.NETCore.Plugins` checkouts. `pack.ps1` calls the core packer and needs the same
+`PluginManager` checkout.
+
+## Invariants
+
+- The loader package is named `hosihikari-csharp`; it routes on `extraInfo.loader: assembly` with
+  entry `Hosihikari.PluginLoader.CSharp.dll`. Source packages it handles use
+  `extraInfo.loader: csharp` and entry `main.cs`.
+- Compile-time references follow the runtime order: framework shared layer, package-local DLLs,
+  then trusted platform assemblies.
+- Cache keys cover source text, package-local DLLs, Roslyn version, and runtime version. Keep the
+  checksum check in sync.
+- A failed load releases its ALC; one package exposes exactly one `IPlugin` type.
+- Public default branches are protected. Work on a branch, open a pull request, and squash merge.
+
+## Context
+
+- [Design record](https://github.com/HosihikariFramework/Design) — GLOSSARY and ADRs.
+- [C# plugin guide](https://hf.srcz.one/authoring-csharp/).