Auto-detect target platform

Dockerfile

@@ -6,7 +6,8 @@ FROM mcr.microsoft.com/dotnet/sdk:9.0 AS build
 
 ARG SOURCE_REPO=https://git.wylab.me/wylab/wylab-station-14.git
 ARG SOURCE_REF=master
-ARG TARGET_PLATFORM=linux-x64
+ARG TARGETPLATFORM
+ARG TARGET_PLATFORM=auto
 
 # Install dependencies needed to build and package the server
 RUN --mount=type=cache,target=/var/cache/apt \
@@ -26,8 +27,19 @@ RUN python3 RUN_THIS.py --quiet
 
 # Build and package the server for the requested platform
 RUN --mount=type=cache,target=/root/.nuget/packages \
+    if [ "${TARGET_PLATFORM}" = "auto" ]; then \
+        case "${TARGETPLATFORM:-linux/amd64}" in \
+            "linux/amd64") SERVER_RID="linux-x64" ;; \
+            "linux/arm64") SERVER_RID="linux-arm64" ;; \
+            "linux/arm/v7"|"linux/arm/v6") SERVER_RID="linux-arm" ;; \
+            *) echo "Unsupported TARGETPLATFORM '${TARGETPLATFORM}'. Set TARGET_PLATFORM explicitly."; exit 1 ;; \
+        esac; \
+    else \
+        SERVER_RID="${TARGET_PLATFORM}"; \
+    fi && \
+    echo "Building server runtime for ${SERVER_RID} (docker TARGETPLATFORM=${TARGETPLATFORM:-unknown})" && \
     dotnet run --project Content.Packaging/Content.Packaging.csproj server \
-        --platform "${TARGET_PLATFORM}" \
+        --platform "${SERVER_RID}" \
         --configuration Release
 
 # Extract packaged build into the filesystem layout the runtime stage expects

README.md

@@ -34,13 +34,22 @@ This project is for those who prefer containerized solutions. It's based on the
     docker build \
       --build-arg SOURCE_REPO=https://git.wylab.me/wylab/wylab-station-14.git \
       --build-arg SOURCE_REF=master \
-      --build-arg TARGET_PLATFORM=linux-x64 \
+      --build-arg TARGET_PLATFORM=auto \
       -t git.wylab.me/wylab/WS14-Docker-Linux-Server:local .
     ```
 
     - `SOURCE_REPO` – Git URL of the content repo to compile (defaults to the wylab fork).
     - `SOURCE_REF` – Branch, tag, or commit to check out (defaults to `master`).
-    - `TARGET_PLATFORM` – Runtime identifier passed to the packaging tool (defaults to `linux-x64`).
+    - `TARGET_PLATFORM` – Runtime identifier passed to the packaging tool. Use `auto` (default) to match the Docker target platform automatically, or override with `linux-x64`, `linux-arm64`, or `linux-arm` to force an architecture.
+
+    If you are building on one architecture and running on another (for example, building on x86 and deploying to an ARM board), build with an explicit platform to avoid `exec format error`:
+
+    ```bash
+    docker buildx build \
+      --platform linux/arm64 \
+      --build-arg TARGET_PLATFORM=linux-arm64 \
+      -t git.wylab.me/wylab/WS14-Docker-Linux-Server:arm64 .
+    ```
 
     The build container clones the selected ref, runs `RUN_THIS.py --quiet` to fetch submodules, and executes `dotnet run --project Content.Packaging server` to generate a release zip that is baked into the final layer.