docs(release): document Windows nightly package

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

3 files changed, 15 insertions, 9 deletions

diff --git a/AGENTS/ARCH.md b/AGENTS/ARCH.md
index 85df6cb..f48fbb1 100644
--- a/AGENTS/ARCH.md
+++ b/AGENTS/ARCH.md
@@ -193,13 +193,19 @@ deletes the release and preserves its tag, title and notes. GitHub's generated
 source downloads remain available.
 
 The Linux compiler and plugin jobs use Ubuntu 24.04 x86_64; the macOS compiler
-job uses a macOS 15 arm64 runner. All three check out the push SHA and run
-independently after cleanup. Both compiler jobs use LLVM/Clang 23, Release and
-EMBEDDED settings, Pandoc, and the existing `release` target. Linux obtains its
-toolchain from apt.llvm.org; macOS uses Homebrew's LLVM 23. Each job extracts
-and checks its archive, then runs a small OUTPUT program with the packaged
-binary. The macOS check also verifies arm64 and rejects non-system dynamic
-libraries. The plugin uses Node.js 22, `npm ci --ignore-scripts` and
+job uses a macOS 15 arm64 runner, and Windows uses Windows Server 2025 x86_64.
+All four check out the push SHA and run independently after cleanup. All three
+compiler jobs use LLVM/Clang 23, Release and EMBEDDED settings, Pandoc, and the
+existing `release` target. Linux obtains its toolchain from apt.llvm.org; macOS
+uses Homebrew's LLVM 23. Windows uses `msys2/setup-msys2@v2` with MINGW64,
+MSYS2 LLVM/Clang packages, explicit native compiler and LLVM paths, and the
+MinGW Makefiles generator. It downloads the official Pandoc 3.12.1 Windows
+x86_64 ZIP into `build/deps/packages/` for CMake to extract. Each compiler job
+extracts and checks its archive, then runs a small OUTPUT program with the
+packaged binary. Windows checks its ZIP in PowerShell with PATH limited to
+Windows system directories, excluding MSYS2 and LLVM. The macOS check also
+verifies arm64 and rejects non-system dynamic libraries. The plugin uses
+Node.js 22, `npm ci --ignore-scripts` and
 `npm run package`, then checks VSIX contents. Each job uploads directly after
 its own checks pass; failure in one does not block the others. No Actions
 artifacts are uploaded.
diff --git a/README.md b/README.md
index 2956124..5081e7d 100644
--- a/README.md
+++ b/README.md
@@ -4,7 +4,7 @@ A compiler for CIE Pseudocode (A Level 9618 Computer Science)
 
 [Usage quick reference](doc/cpsc.1.md) · [Build guide](doc/build.md) · [Installation and releases](doc/install.md)
 
-Download the Linux x86_64 or macOS 15+ Apple Silicon compiler package and VS Code extension from [Nightly Build](https://github.com/ovfor4/cie-pseudocode-compiler/releases/tag/nightly-build). The compiler uses EMBEDDED mode and needs no LLVM installation. Each push to `main` removes the previous attachments before rebuilding all three packages; each package appears when its build and checks finish.
+Download the Linux x86_64, Windows x86_64 or macOS 15+ Apple Silicon compiler package and VS Code extension from [Nightly Build](https://github.com/ovfor4/cie-pseudocode-compiler/releases/tag/nightly-build). The compiler uses EMBEDDED mode and needs no LLVM installation. Each push to `main` removes the previous attachments before rebuilding all four packages; each package appears when its build and checks finish.
 
 Details can be found here: [Pseudocode Guide for Teachers](https://www.cambridgeinternational.org/Images/697401-2026-pseudocode-guide-for-teachers.pdf)
 
diff --git a/doc/install.md b/doc/install.md
index b734f77..a8e8a2e 100644
--- a/doc/install.md
+++ b/doc/install.md
@@ -2,7 +2,7 @@
 
 To build from source, follow [build.md](build.md). For command-line usage, see [cpsc.1.md](cpsc.1.md). Run build commands from the project root; package installation commands run from the extracted package directory.
 
-The [Nightly Build](https://github.com/ovfor4/cie-pseudocode-compiler/releases/tag/nightly-build) provides EMBEDDED release archives for Linux x86_64 and macOS 15+ Apple Silicon, plus the VS Code extension. The macOS archive is named `cpsc-VERSION-Darwin-arm64.tar.xz`; use the Unix release package instructions below after extraction.
+The [Nightly Build](https://github.com/ovfor4/cie-pseudocode-compiler/releases/tag/nightly-build) provides EMBEDDED release archives for Linux x86_64, Windows x86_64 and macOS 15+ Apple Silicon, plus the VS Code extension. The macOS archive is named `cpsc-VERSION-Darwin-arm64.tar.xz`; use the Unix release package instructions below after extraction. For Windows, download `cpsc-VERSION-Windows-ARCH.zip` and follow the Windows release package instructions below; no LLVM or MSYS2 installation is required to run it.
 
 ## Linux installation