feat(docker): add Windows cross-compilation support via Docker

Add Dockerfile.windows and build-windows.sh for cross-compiling Windows executables
in a containerized environment. Includes documentation updates in README.md with
build instructions and troubleshooting tips for Windows builds.

docker-build/Dockerfile.windows

@@ -0,0 +1,18 @@
+FROM ubuntu:20.04
+
+ENV DEBIAN_FRONTEND=noninteractive TZ=UTC
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    build-essential libtool autotools-dev automake autoconf pkg-config \
+    bsdmainutils python3 curl ca-certificates git unzip zip file rsync \
+    g++-mingw-w64-x86-64 binutils-mingw-w64-x86-64 nsis \
+ && rm -rf /var/lib/apt/lists/*
+
+RUN update-alternatives --set x86_64-w64-mingw32-g++ /usr/bin/x86_64-w64-mingw32-g++-posix || true && \
+    update-alternatives --set x86_64-w64-mingw32-gcc /usr/bin/x86_64-w64-mingw32-gcc-posix || true
+
+WORKDIR /src
+
+COPY . /src
+
+CMD ["/bin/bash"]

docker-build/README.md

@@ -63,3 +63,66 @@ docker run --rm -it -v "$(pwd)/../build/linux-x86_64":/out palladium-builder:lin
 **Docker build issues:** Ensure Docker has sufficient resources and the daemon is running
 
 **Missing dependencies:** The Dockerfile installs all required build dependencies automatically
+
+## Windows x86_64 Build
+
+### Overview
+
+This build creates Windows x86_64 executables using cross-compilation in a Docker container based on Ubuntu 20.04. The build process:
+
+1. **Builds a Docker image** (`palladium-builder:windows-ubuntu20.04`) containing MinGW-w64 cross-compilation toolchain
+2. **Copies the entire repository** into the container during image build
+3. **Cross-compiles for Windows** using the `depends` system with `x86_64-w64-mingw32` target
+4. **Outputs .exe files** to a mounted volume for host access
+
+### Quick Start
+
+```bash
+cd docker-build
+chmod +x build-windows.sh
+./build-windows.sh
+```
+
+Windows executables will be available in `../build/windows/` directory.
+
+### Prerequisites
+
+- Docker installed and running ([installation guide](https://docs.docker.com/get-docker/))
+- Sufficient disk space for the build process (at least 12 GB free)
+- Internet connection for downloading dependencies and MinGW-w64 toolchain
+
+### Produced Executables
+
+The following Windows executables are built and copied to the output directory:
+
+- `palladiumd.exe`: Main daemon
+- `palladium-cli.exe`: Command-line client
+- `palladium-tx.exe`: Transaction utility
+- `palladium-wallet.exe`: Wallet utility
+- `palladium-qt.exe`: GUI application (if Qt dependencies are available)
+
+### Output Directory
+
+Executables are placed in: `../build/windows/` (relative to the docker-build directory)
+
+### Cross-Compilation Details
+
+- **Target Triple**: `x86_64-w64-mingw32`
+- **Toolchain**: MinGW-w64 cross-compiler
+- **Dependencies**: Built using the `depends` system for Windows target
+- **Configuration**: Uses `CONFIG_SITE` for proper cross-compilation setup
+
+### Troubleshooting
+
+**Permission errors:** The build script automatically handles file permissions using host UID/GID
+
+**Build failed:** Run interactive container for debugging:
+```bash
+docker run --rm -it -v "$(pwd)/../build/windows":/out palladium-builder:windows-ubuntu20.04 bash
+```
+
+**Cross-compilation issues:** Ensure the MinGW-w64 toolchain is properly installed in the container
+
+**Missing .exe files:** Check that the configure script detected the Windows target correctly
+
+**Docker build issues:** Ensure Docker has sufficient resources and the daemon is running

docker-build/build-windows.sh

@@ -0,0 +1,63 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+IMAGE_NAME="palladium-builder:windows-ubuntu20.04"
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+REPO_DIR="$(cd "${SCRIPT_DIR}/.." && pwd)"
+OUT_DIR="${REPO_DIR}/build/windows"
+HOST_TRIPLE="x86_64-w64-mingw32"
+
+HOST_UID="$(id -u)"
+HOST_GID="$(id -g)"
+
+echo "[*] Building Docker image including the ENTIRE repository (COPY . /src)..."
+
+docker build --platform=linux/amd64 \
+  -t "$IMAGE_NAME" \
+  -f "${SCRIPT_DIR}/Dockerfile.windows" \
+  "${REPO_DIR}"
+
+mkdir -p "${OUT_DIR}"
+
+echo "[*] Starting container: build COMPLETELY in container; mount ONLY the output..."
+docker run --rm --platform=linux/amd64 \
+  -e HOST_UID="${HOST_UID}" -e HOST_GID="${HOST_GID}" \
+  -v "${OUT_DIR}":/out \
+  "$IMAGE_NAME" \
+  bash -c "
+    set -euo pipefail
+    cd /src
+
+    echo '[*] depends (Windows cross, HOST=${HOST_TRIPLE})...'
+    cd depends && make HOST=${HOST_TRIPLE} -j\$(nproc) && cd ..
+
+    echo '[*] autogen/configure...'
+    [[ -x ./autogen.sh ]] && ./autogen.sh
+    [[ -f ./configure ]] || { echo 'configure not found: autogen failed'; exit 1; }
+
+    # For Windows with depends: use CONFIG_SITE and prefix=/
+    CONFIG_SITE=\$PWD/depends/${HOST_TRIPLE}/share/config.site \
+      ./configure --prefix=/
+
+    echo '[*] make...'
+    make -j\$(nproc)
+
+    echo '[*] copying .exe files to /out...'
+    mkdir -p /out
+    # Typical executables (update the names if your project produces different ones)
+    for b in \
+      src/palladiumd.exe \
+      src/palladium-cli.exe \
+      src/palladium-tx.exe \
+      src/palladium-wallet.exe \
+      src/qt/palladium-qt.exe; do
+      [[ -f \"\$b\" ]] && install -m 0755 \"\$b\" /out/
+    done
+
+    # Align permissions to host user
+    chown -R \${HOST_UID:-0}:\${HOST_GID:-0} /out
+
+    echo '[*] build COMPLETED (everything in container) → /out'
+  "
+
+echo "[*] Windows executables available in: ${OUT_DIR}"