Update project structure and build process

recovery_tool/Dockerfile

@@ -0,0 +1,79 @@
+# Building this Dockerfile executes a full build of the Recovery Tool, cross-compiling inside 
+# the container. The resulting executable is copied to the output directory using Docker BuildKit.
+
+# You need to pass 3 parameters via --build-arg:
+# 1. `os`  : the GOOS env var -- `linux`, `windows` or `darwin`.
+# 2. `arch`: the GOARCH env var -- `386` or `amd64` (note that darwin/386 is not a thing).
+# 3. `cc`  : the CC env var -- a C compiler for CGO to use, empty to use the default.
+# 4. `out` : the name of the resulting executable, placed in the output directory on the host.
+
+# For example, to build a linux/386 binary into `bin/rt`:
+#   docker build . --output bin --build-arg os=linux --build-arg arch=386 --build-arg out=rt
+
+# Note that the --output <dir> flag refers to the host, outside the container.
+
+# --------------------------------------------------------------------------------------------------
+
+# We have to different base images: one for arm and one for amd.
+# Turns out that debian gcc packages assume the current is always the "gcc" package, but 
+# for other archs it's "gcc-multilib-${arch}-linux-gnu". This makes it impossible to build
+# one command that downloads all the archs we want for both amd64 and arm64 runners.
+# The solution is to have one base layer per arch.
+
+FROM golang:1.22.6-bookworm AS rtool-build-base-arm64
+
+# Avoid prompts during package installation:
+ENV DEBIAN_FRONTEND="noninteractive"
+
+# Upgrade indices:
+RUN apt-get update
+
+# Install the various compilers we're going to use, with specific versions:
+RUN apt-get install -y \
+  gcc-mingw-w64 \
+  gcc-12-multilib-i686-linux-gnu \
+  gcc-12-multilib-x86-64-linux-gnu
+
+FROM golang:1.22.6-bookworm AS rtool-build-base-amd64
+
+# Avoid prompts during package installation:
+ENV DEBIAN_FRONTEND="noninteractive"
+
+# Upgrade indices:
+RUN apt-get update
+
+# Install the various compilers we're going to use, with specific versions:
+RUN apt-get install -y \
+  gcc-mingw-w64 \
+  gcc-12-multilib-i686-linux-gnu \
+  gcc-12-aarch64-linux-gnu
+
+FROM rtool-build-base-${TARGETARCH} AS rtool-build-base
+
+# Copy the source code into the container:
+WORKDIR /src
+COPY . .
+
+RUN /bin/bash
+
+# --------------------------------------------------------------------------------------------------
+
+FROM rtool-build-base AS rtool-build
+ARG os
+ARG arch
+ARG cc
+
+# Enable and configure C support:
+ENV CGO_ENABLED=1
+ENV GO386=softfloat
+
+# Do the thing:
+RUN env GOOS=${os} GOARCH=${arch} CC=${cc} go build -mod=vendor -a -trimpath -o /out ./recovery_tool/
+
+# --------------------------------------------------------------------------------------------------
+
+FROM scratch
+ARG out
+
+# Copy the resulting executable back to the host:
+COPY --from=rtool-build /out ${out}