Add linux_arm64 builds for Ebitengine and Bevy

Batocera and the ES-family distributions run on ARM as much as on
x86_64 — Raspberry Pi, Odroid, the retro handhelds — and a linux_x64
binary installs there but will not start. There was no Linux ARM asset
kind at all: KINDS had linux_x86 and linux_x64 and mac_arm64, but
nothing for 64-bit ARM Linux.

Registering the kind is deliberately separate from producing it: a
platform service only includes BuildLinuxArm64 once its pipeline builds
the artifact, otherwise /api/builds would report it missing for every
release. Hence Ebitengine and Bevy only. Godot needs a Linux arm64
export preset in each game repo first; LÖVE fuses an upstream AppImage
that ships x86_64 only; TIC-80's export command has no ARM target.

Ebitengine needs cgo on Linux, so binary_build gained a cross-compiler
argument — and unsets CC for native targets, otherwise a build after
the ARM one silently picks up the cross gcc.

Verified by cross-compiling both demos in the rebuilt images: each
produced a genuine AArch64 ELF (e_machine 183), not a silent fallback.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

app/models/warp_engine/release_asset.rb

@@ -1,7 +1,7 @@
 module WarpEngine
   class ReleaseAsset < ApplicationRecord
     KINDS = %w[cartridge source html docs
-               win_x86 win_x64 linux_x86 linux_x64
+               win_x86 win_x64 linux_x86 linux_x64 linux_arm64
                mac_x64 mac_arm64 mac_universal].freeze
 
     belongs_to :release

app/services/concerns/warp_engine/platforms/builds/build_linux_arm64.rb

@@ -0,0 +1,28 @@
+module WarpEngine
+  module Platforms
+    module Builds
+      # Linux on 64-bit ARM: Raspberry Pi 4/5, Odroid, and the retro handhelds.
+      # Batocera and the ES-family distributions run on these as much as on
+      # x86_64, and an x64 binary installs there but will not start — which is
+      # why this is a separate kind rather than something linux_x64 can cover.
+      #
+      # Include this in a platform service only once its pipeline actually
+      # produces the artifact: registering the kind makes /api/builds report it
+      # as missing for every release until then.
+      module BuildLinuxArm64
+        extend ActiveSupport::Concern
+
+        included do
+          register_expected_kind "linux_arm64"
+        end
+
+        private
+
+        def linux_arm64_asset_path(versioned)
+          path = full_path("#{versioned}-linux-arm64.zip")
+          { "linux_arm64" => path } if File.file?(path)
+        end
+      end
+    end
+  end
+end

app/services/warp_engine/platforms/bevy/pipeline.yaml.erb

@@ -65,6 +65,15 @@ steps:
         CARGO_TARGET_X86_64_PC_WINDOWS_GNU_LINKER=x86_64-w64-mingw32-gcc \
           cargo build --release --target x86_64-pc-windows-gnu
         pack_binary "win-x64" "target/x86_64-pc-windows-gnu/release/<%= name %>.exe" "<%= name %>.exe"
+        # linux-arm64: Raspberry Pi, Odroid, retro handhelds. pkg-config has to
+        # be told it may cross, and pointed at the arm64 .pc files, otherwise
+        # alsa-sys/libudev-sys pick up the host x86_64 libraries.
+        echo "==> Building linux-arm64 binary"
+        PKG_CONFIG_ALLOW_CROSS=1 \
+          PKG_CONFIG_PATH=/usr/lib/aarch64-linux-gnu/pkgconfig \
+          CARGO_TARGET_AARCH64_UNKNOWN_LINUX_GNU_LINKER=aarch64-linux-gnu-gcc \
+          cargo build --release --target aarch64-unknown-linux-gnu
+        pack_binary "linux-arm64" "target/aarch64-unknown-linux-gnu/release/<%= name %>" "<%= name %>"
 
   - name: upload
     image: alpine
@@ -81,7 +90,7 @@ steps:
         META_DST="<%= name %>-$VERSION.metadata.json"
         cp $META_SRC $META_DST
         BINS=""
-        for slug in win-x64 linux-x64; do
+        for slug in win-x64 linux-x64 linux-arm64; do
           [ -f "<%= name %>-$VERSION-$slug.zip" ] && BINS="$BINS <%= name %>-$VERSION-$slug.zip"
         done
         for f in $FILE $META_DST $BINS; do

app/services/warp_engine/platforms/bevy/service.rb

@@ -6,6 +6,7 @@ module WarpEngine
         include Builds::BuildWeb
         include Builds::BuildWinX64
         include Builds::BuildLinuxX64
+        include Builds::BuildLinuxArm64
 
         label "Bevy"
       end

app/services/warp_engine/platforms/ebitengine/pipeline.yaml.erb

@@ -44,11 +44,14 @@ steps:
         # helper: builds one target + zips it with a single root folder
         # (unix zip keeps the executable bit)
         binary_build() {
-          B_GOOS="$1"; B_GOARCH="$2"; B_CGO="$3"; B_EXT="$4"; B_TARGET="$5"
+          B_GOOS="$1"; B_GOARCH="$2"; B_CGO="$3"; B_EXT="$4"; B_TARGET="$5"; B_CC="$6"
           PKG_DIR="<%= name %>-$VERSION-$B_TARGET"
           echo "==> Building $PKG_DIR"
           rm -rf "$PKG_DIR" "$PKG_DIR.zip"
           mkdir -p "$PKG_DIR"
+          # cgo cross-compile needs an explicit cross gcc; a native build must
+          # not see CC at all, otherwise go picks the wrong compiler
+          if [ -n "$B_CC" ]; then export CC="$B_CC"; else unset CC; fi
           CGO_ENABLED=$B_CGO GOOS=$B_GOOS GOARCH=$B_GOARCH go build -o "$PKG_DIR/<%= name %>$B_EXT" .
           if [ -f LICENSE ]; then cp LICENSE "$PKG_DIR/"; fi
           if [ -f README.md ]; then cp README.md "$PKG_DIR/"; fi
@@ -56,10 +59,13 @@ steps:
           rm -rf "$PKG_DIR"
           echo "==> $PKG_DIR.zip kesz"
         }
-        # CI (linux builder) builds these three:
+        # CI (linux builder) builds these four:
         binary_build "windows" "386" "0" ".exe" "win-x86"
         binary_build "windows" "amd64" "0" ".exe" "win-x64"
         binary_build "linux" "amd64" "1" "" "linux-x64"
+        # linux-arm64: Raspberry Pi, Odroid, retro handhelds — cgo cross-build
+        # against the arm64 X11/GL/ALSA headers in the builder image
+        binary_build "linux" "arm64" "1" "" "linux-arm64" "aarch64-linux-gnu-gcc"
 
   - name: artifact
     image: alpine

app/services/warp_engine/platforms/ebitengine/service.rb

@@ -7,6 +7,7 @@ module WarpEngine
         include Builds::BuildWinX86
         include Builds::BuildWinX64
         include Builds::BuildLinuxX64
+        include Builds::BuildLinuxArm64
         include Builds::BuildMacX64
         include Builds::BuildMacArm64
 

lib/warp_engine/version.rb

@@ -1,3 +1,3 @@
 module WarpEngine
-  VERSION = "0.2.0"
+  VERSION = "0.3.0"
 end