Force asset build stages to run on native platform with --platform=$BUILDPLATFORM

Added --platform=$BUILDPLATFORM to composer-deps and assets stages to ensure they run on the native build platform (amd64) instead of being built separately for each target architecture (amd64, arm64, arm/v7).

This is the critical change that makes the optimization work:
- Without this flag, Docker Buildx builds these stages for each target platform
- With this flag, stages run once on native platform and results are copied to all targets
- Eliminates ARM emulation overhead for CPU-intensive asset compilation

Co-authored-by: jbtronics <[email protected]>

Author: Copilot

Dockerfile

@@ -4,7 +4,9 @@ ARG PHP_VERSION=8.4
 # ---
 # Build assets stage - runs on native platform (not emulated)
 # This stage builds the frontend assets (JavaScript, CSS) using Node.js and Yarn
-FROM composer:latest AS composer-deps
+# The --platform=$BUILDPLATFORM ensures this stage runs on the native build platform (amd64)
+# and not under emulation for ARM builds
+FROM --platform=$BUILDPLATFORM composer:latest AS composer-deps
 
 WORKDIR /build
 
@@ -19,7 +21,7 @@ RUN composer install --no-dev --no-scripts --no-autoloader --prefer-dist --ignor
 
 # ---
 
-FROM node:22-bookworm-slim AS assets
+FROM --platform=$BUILDPLATFORM node:22-bookworm-slim AS assets
 
 WORKDIR /build
 

Dockerfile-frankenphp

@@ -1,7 +1,9 @@
 # ---
 # Build assets stage - runs on native platform (not emulated)
 # This stage builds the frontend assets (JavaScript, CSS) using Node.js and Yarn
-FROM composer:latest AS composer-deps
+# The --platform=$BUILDPLATFORM ensures this stage runs on the native build platform (amd64)
+# and not under emulation for ARM builds
+FROM --platform=$BUILDPLATFORM composer:latest AS composer-deps
 
 WORKDIR /build
 
@@ -16,7 +18,7 @@ RUN composer install --no-dev --no-scripts --no-autoloader --prefer-dist --ignor
 
 # ---
 
-FROM node:22-bookworm-slim AS assets
+FROM --platform=$BUILDPLATFORM node:22-bookworm-slim AS assets
 
 WORKDIR /build