fix(docker): Replace emsdk image with Ubuntu + emsdk from source

The Docker build used emscripten/emsdk:4.0.2-arm64 as base image but
env.sh couldn't find emsdk there, installing a second copy. The build
then applied wasm-opt/finalize stubs to the wrong emsdk (hardcoded
/emsdk/), so the real wasm-emscripten-finalize ran in Docker and got
OOM-killed.

- Use ubuntu:22.04 base with emsdk installed from source at /emsdk/
- Make stub paths dynamic via $EMSDK instead of hardcoded /emsdk/
- Skip local emsdk install in env.sh when $EMSDK is already active

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docker/Dockerfile

@@ -1,5 +1,7 @@
-# Use ARM64-native image for Apple Silicon (M1/M2/M3/M4)
-FROM emscripten/emsdk:4.0.2-arm64
+# Plain Ubuntu base — multi-arch (ARM64/x86_64 auto-detected)
+FROM ubuntu:22.04
+
+ENV DEBIAN_FRONTEND=noninteractive
 
 # Install build tools required for KiCad WASM build
 RUN apt-get update && apt-get install -y \
@@ -19,8 +21,17 @@ RUN apt-get update && apt-get install -y \
     unixodbc-dev \
     ccache \
     rsync \
+    xz-utils \
     && rm -rf /var/lib/apt/lists/*
 
+# Install emsdk from source (same approach as scripts/setup-emsdk.sh)
+# EMSCRIPTEN_VERSION must match scripts/common/versions.sh
+ARG EMSCRIPTEN_VERSION=4.0.2
+RUN git clone https://github.com/emscripten-core/emsdk.git /emsdk \
+    && cd /emsdk \
+    && ./emsdk install ${EMSCRIPTEN_VERSION} \
+    && ./emsdk activate ${EMSCRIPTEN_VERSION}
+
 # Configure ccache for Emscripten
 # CCACHE_DIR in named volume persists across containers
 ENV CCACHE_DIR=/workspace/build-wasm/.ccache

scripts/common/env.sh

@@ -36,18 +36,26 @@ export WX_BUILD="$BUILD_ROOT/wxwidgets-universal"
 # Emscripten settings
 export EMSDK_QUIET=1
 
-# Local emsdk: auto-install if missing, then source its environment
-# The emsdk bundles its own Python, Node, and LLVM — no Homebrew needed
-_EMSDK_DIR="$_KICAD_WASM_PROJECT_ROOT/tools/emsdk"
-_EMSDK_ENV="$_EMSDK_DIR/emsdk_env.sh"
+# Emscripten SDK setup
+# If EMSDK is already set (e.g. Docker entrypoint sourced emsdk_env.sh), use it.
+# Otherwise auto-install a local copy under tools/emsdk/.
+if [ -n "$EMSDK" ] && [ -f "$EMSDK/emsdk_env.sh" ]; then
+    # emsdk already active (e.g., Docker entrypoint sourced it)
+    source "$EMSDK/emsdk_env.sh" 2>/dev/null
+else
+    # Local emsdk: auto-install if missing, then source its environment
+    # The emsdk bundles its own Python, Node, and LLVM — no Homebrew needed
+    _EMSDK_DIR="$_KICAD_WASM_PROJECT_ROOT/tools/emsdk"
+    _EMSDK_ENV="$_EMSDK_DIR/emsdk_env.sh"
 
-if [ ! -f "$_EMSDK_ENV" ]; then
-    echo "Emscripten SDK not found. Installing..."
-    "$_KICAD_WASM_SCRIPTS_DIR/setup-emsdk.sh"
-fi
+    if [ ! -f "$_EMSDK_ENV" ]; then
+        echo "Emscripten SDK not found. Installing..."
+        "$_KICAD_WASM_SCRIPTS_DIR/setup-emsdk.sh"
+    fi
 
-if [ -f "$_EMSDK_ENV" ]; then
-    source "$_EMSDK_ENV" 2>/dev/null
+    if [ -f "$_EMSDK_ENV" ]; then
+        source "$_EMSDK_ENV" 2>/dev/null
+    fi
 fi
 
 # Common compiler flags

scripts/kicad/build-pcbnew.sh

@@ -181,7 +181,11 @@ log_info "Stub libraries built"
 # Step 6.2: Replace Emscripten's wasm-opt with stub to bypass asyncify transformation
 # This allows Emscripten to generate JS with Asyncify runtime, but we run the real
 # wasm-opt --asyncify on the host where more RAM is available (needs 50GB+ for KiCad)
-EMSDK_WASM_OPT="/emsdk/upstream/bin/wasm-opt"
+if [ -z "${EMSDK}" ]; then
+    log_error "EMSDK environment variable is not set."
+    exit 1
+fi
+EMSDK_WASM_OPT="${EMSDK}/upstream/bin/wasm-opt"
 if [ -f "${EMSDK_WASM_OPT}" ] && [ ! -f "${EMSDK_WASM_OPT}.real" ]; then
     log_info "Backing up real wasm-opt..."
     mv "${EMSDK_WASM_OPT}" "${EMSDK_WASM_OPT}.real"
@@ -193,7 +197,7 @@ log_info "wasm-opt stub installed (asyncify will run on host)"
 
 # Step 6.3: Replace wasm-emscripten-finalize with stub (same pattern as wasm-opt)
 # This tool also OOMs on large WASM with debug symbols, so we run it on the host
-EMSDK_FINALIZE="/emsdk/upstream/bin/wasm-emscripten-finalize"
+EMSDK_FINALIZE="${EMSDK}/upstream/bin/wasm-emscripten-finalize"
 if [ -f "${EMSDK_FINALIZE}" ] && [ ! -f "${EMSDK_FINALIZE}.real" ]; then
     log_info "Backing up real wasm-emscripten-finalize..."
     mv "${EMSDK_FINALIZE}" "${EMSDK_FINALIZE}.real"