Fix arm64 sandbox image build: TARGETARCH default shadows BuildKit auto-injection#88
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sandbox-image-release.yml's (local, parsar-sandbox, ...) matrix leg failed on its first run after merge: /tmp/install-agents.sh: line 72: /usr/local/bin/claude: No such file or directory Root cause: infra/sandbox/Dockerfile's runtime stage declared `ARG TARGETARCH=amd64`. BuildKit auto-populates TARGETARCH per target platform for every node in a multi-platform build graph, but a hardcoded default on a re-declared ARG shadows that auto-injection instead of merely being a fallback — every platform, including the arm64 build graph node, silently resolved TARGETARCH=amd64. install-agents.sh then downloaded the x86_64 Claude Code binary and tried to run it on an aarch64 rootfs; the kernel can't find the ELF interpreter for a wrong-architecture binary, which surfaces as ENOENT rather than the more obvious "exec format error". Fix: bare `ARG TARGETARCH` (no default), matching the go-builder stage's existing correct pattern. Verified without a full slow QEMU-emulated build (this repro alone took over the CI job's whole ~5min budget): built two throwaway one-line Dockerfiles differing only in the ARG TARGETARCH declaration, each targeting --platform linux/arm64. `ARG TARGETARCH=amd64` printed "amd64" (reproducing the bug in isolation); bare `ARG TARGETARCH` printed "arm64" (confirms the fix). Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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Summary
sandbox-image-release.yml'slocal(parsar-sandbox) matrix leg failed on its first run after #87 merged:Root cause:
infra/sandbox/Dockerfile's runtime stage hadARG TARGETARCH=amd64. BuildKit auto-populatesTARGETARCHper target platform for every node in a multi-platform build graph, but giving it a hardcoded default on a re-declaredARGshadows that auto-injection instead of acting as a mere fallback — every platform, including thearm64build graph node, silently resolvedTARGETARCH=amd64.install-agents.shthen downloaded the x86_64 Claude Code binary and tried to run it on an aarch64 rootfs; the kernel can't find the ELF interpreter for a wrong-architecture binary, which surfaces asENOENTrather than the more obvious "exec format error".Fix: bare
ARG TARGETARCH(no default), matching thego-builderstage's existing correct pattern — thee2bmatrix leg (amd64-only) is unaffected either way since BuildKit's auto value for an amd64 build is alreadyamd64.Test plan
ARG TARGETARCHdeclaration, each targeting--platform linux/arm64.ARG TARGETARCH=amd64printed"amd64"(reproduces the bug in isolation); bareARG TARGETARCHprinted"arm64"(confirms the fix)sandbox imagesworkflow should now succeed on both matrix legs after merge🤖 Generated with Claude Code