Add GitHub Copilot instructions / AGENTS.md (#1289)

Author: lbussell

AGENTS.md

@@ -0,0 +1,71 @@
+# Coding Agent Instructions for dotnet-framework-docker
+
+This repository contains the official Docker images for .NET Framework, published to Microsoft Container Registry (mcr.microsoft.com).
+
+## Build and Test Commands
+
+```powershell
+# Build and test all images for a specific .NET version
+./build-and-test.ps1 -Version 4.8
+
+# Build only (no tests) for specific version and OS
+./build-and-test.ps1 -Version 4.8 -OS windowsservercore-ltsc2019 -Mode Build
+
+# Test only
+./build-and-test.ps1 -Version 4.8 -Mode Test
+
+# Build/test specific image variants: runtime, sdk, aspnet, wcf
+./build-and-test.ps1 -Repos sdk -Version 4.8.1
+
+# Run a single test by filter
+./tests/run-tests.ps1 -TestCategories sdk
+dotnet test tests/Microsoft.DotNet.Framework.Docker.Tests --filter "Category=sdk"
+```
+
+## Architecture
+
+### Image Hierarchy
+
+Images build on each other: `runtime` → `aspnet` → `wcf`, with `sdk` building on `runtime`. Each variant supports multiple .NET Framework versions (4.8, 4.8.1) across Windows Server Core versions (ltsc2016, ltsc2019, ltsc2022, ltsc2025).
+
+### Generated Files (Do Not Edit Directly)
+
+- **Dockerfiles in `src/`**: Generated from [Cottle templates](https://cottle.readthedocs.io/en/stable/) in `eng/dockerfile-templates/`
+- **README files**: Generated from templates in `eng/readme-templates/`
+
+To modify Dockerfiles or READMEs, edit the templates and regenerate:
+
+```powershell
+# Regenerate Dockerfiles
+./eng/dockerfile-templates/Get-GeneratedDockerfiles.ps1
+
+# Regenerate READMEs
+./eng/readme-templates/Get-GeneratedReadmes.ps1
+
+# Validate without regenerating
+./eng/dockerfile-templates/Get-GeneratedDockerfiles.ps1 -Validate
+```
+
+### Key Configuration Files
+
+- `manifest.json`: Defines all images, tags, and build configuration for the infrastructure
+- `manifest.versions.json`: Product versions (NuGet, Visual Studio, patches) referenced by Dockerfile templates
+- `manifest.datestamps.json`: Date-based tags for image versioning
+
+## Conventions
+
+### Dockerfile Template Variables
+
+Templates use Cottle syntax with variables from `manifest.versions.json`:
+
+- `VARIABLES[cat("kb|", OS_VERSION_NUMBER, "|", PRODUCT_VERSION)]` - Windows KB patches
+- `VARIABLES[cat(PRODUCT_VERSION, "|url")]` - .NET Framework installer URLs
+- `OS_VERSION_NUMBER`, `PRODUCT_VERSION` - Context variables for the build
+
+### Test Categories
+
+Tests are categorized by image type: `runtime`, `sdk`, `aspnet`, `wcf`, `pre-build`. Tests validate both static image state (environment variables) and runtime scenarios.
+
+### Updating Product Versions
+
+Update `manifest.versions.json` then regenerate Dockerfiles. This is typically done by automation.

eng/pipelines/dotnet-framework-pr.yml

@@ -8,6 +8,7 @@ pr:
     exclude:
     - .github/*
     - README*
+    - AGENTS*
     - samples/*
 
 resources: