CI: Docker build for ARM64 too

[metachris]

Add ARM64 as target platform for Docker builds.

[Copilot]

Pull request overview

This PR adds ARM64 architecture support to the Docker build pipeline, enabling multi-platform image builds for both AMD64 and ARM64 architectures.

Changes:

• Updated Docker build platform configuration to include linux/arm64 alongside existing linux/amd64

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[claude]

Claude finished @metachris's task in 56s —— View job

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Review Summary

LGTM ✓

This is a well-structured, minimal change that adds ARM64 as a target platform for Docker builds.

Analysis

What changed:

• Line 317: platforms: linux/amd64 → platforms: linux/amd64,linux/arm64

Verification:

1. Dockerfile is already ARM64-ready: The docker/Dockerfile.rbuilder already handles multi-platform builds correctly:

   • Uses TARGETPLATFORM build argument (line 13)
   • Has platform-specific logic for sccache binary downloads (lines 22-30) supporting both linux/amd64 and linux/arm64
   • Uses platform-agnostic base images (rust:1.89-bookworm, gcr.io/distroless/cc-debian12)

2. Workflow has proper prerequisites: The workflow already includes:

   • QEMU setup (docker/setup-qemu-action@v3 at line 282) for cross-platform emulation
   • Buildx setup (docker/setup-buildx-action@v3 at line 285) for multi-platform builds

Considerations

Build time impact: ARM64 builds via QEMU emulation on x64 runners can be significantly slower than native builds. This is expected behavior but worth noting for CI timing expectations.

No issues found - the change is correct and all prerequisites for multi-platform builds are already in place.

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[ZanCorDX]

Took more than 2hs to build.