fix(container): pin UV binary to build platform in cross-compilation stages

[raballew]

Summary

• Fixes multi-platform Docker builds failing with qemu-aarch64: Could not open '/lib/ld-linux-aarch64.so.1'
• COPY --from=<multi-platform-image> resolves the source image against the target platform, not the stage platform. In builder stages pinned to $BUILDPLATFORM, this copies an aarch64 UV binary into an amd64 container. The statically-linked UV binary runs via QEMU, but the dynamically-linked Python it downloads cannot find the aarch64 dynamic linker.
• Uses a named stage pinned to $BUILDPLATFORM for the UV image so COPY always gets the native-architecture binary

Failing CI run: https://github.com/jumpstarter-dev/jumpstarter/actions/runs/27947151753/job/82694686925

Test plan

• CI multi-platform image build passes without QEMU dynamic linker errors
• Add build-pr-images label to trigger the image builds

🤖 Generated with Claude Code

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 01ca6ba9-937a-4838-b7cd-ca4fcaf91e2f

📥 Commits

Reviewing files that changed from the base of the PR and between deed30c and 0bc05af.

📒 Files selected for processing (4)

• python/.devfile/Containerfile.client
• python/.gitignore
• python/Containerfile
• python/Makefile

✅ Files skipped from review due to trivial changes (1)

• python/.gitignore

🚧 Files skipped from review as they are similar to previous changes (2)

• python/.devfile/Containerfile.client
• python/Containerfile

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📝 Walkthrough

Walkthrough

Both python/Containerfile and python/.devfile/Containerfile.client introduce a dedicated uv-bin intermediate build stage based on ghcr.io/astral-sh/uv. The subsequent COPY instructions now reference this named stage alias instead of copying directly from the pinned image reference. Additionally, the Makefile is updated to configure per-package uv cache directories during test execution, with corresponding .gitignore entries to exclude cache artifacts from version control.

Changes

uv Build and Test Infrastructure

Layer / File(s)	Summary
Introduce uv-bin named stage python/Containerfile, python/.devfile/Containerfile.client	Both files add FROM ghcr.io/astral-sh/uv:... AS uv-bin and update COPY --from=uv-bin to pull /uv, /uvx, and /bin/ from the named stage instead of referencing the image directly.
Per-package uv cache directory support python/Makefile, python/.gitignore	Makefile pkg-test-% target sets UV_CACHE_DIR to $(CURDIR)/.uv-cache/$* for isolated per-package caching, clean-test removes .uv-cache, and .gitignore adds .uv-cache/ ignore pattern.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Possibly related PRs

• jumpstarter-dev/jumpstarter#749: Updates the same ghcr.io/astral-sh/uv image tag and COPY source in the same Containerfiles, directly overlapping with the build stage wiring changed here.

Suggested reviewers

• mangelajo

Poem

A bunny hops through Docker layers neat,
A uv-bin stage makes the build complete!
Per-package caches hop so neatly by,
Named stages now let the artifacts fly.
🐇✨ Clean and tidy, cache tucked away!

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title directly and specifically describes the main change: pinning the UV binary to the build platform in cross-compilation Docker stages to fix multi-platform builds.
Description check	✅ Passed	The description is directly related to the changeset, explaining the problem, root cause, and solution implemented across the modified Dockerfiles and configuration files.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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