ci: pin pixi-version in setup-pixi for deterministic lock validation

[xraymemory]

Problem

CI validates the lockfile with pixi install --locked (strict — it fails rather than re-solving if pixi.lock doesn't match pyproject.toml). But setup-pixi@v0.8.8 pins the action, not the pixi binary — it installs whatever pixi is "latest" at run time.

So the pixi that generates a lock locally can differ from the pixi that validates it in CI, and two versions can disagree on the manifest hash. The symptom is intermittent lock file not up-to-date with the workspace failures on PRs that didn't touch dependencies (seen on #300), and CI that can start failing with no code change when a new pixi ships.

Fix

Pin pixi-version: v0.73.0 on every setup-pixi step (ci.yml x3, gpu-tests.yml). v0.73.0 is the version that generated the current green lock on main. Lock validation is now deterministic and matches the committed lock's generator.

Follow-up

Contributors regenerating the lock should use the same pinned pixi (pixi self-update --version 0.73.0 or install that version), run pixi lock, and commit pyproject.toml + pixi.lock together. Bumping pixi later is a one-line change here plus a relock.

Summary by CodeRabbit

• Chores
  • Standardized the Pixi toolchain version used by automated linting, type checks, CPU tests, and GPU tests.
  • Improved consistency and reproducibility across continuous integration workflows.

[coderabbitai]

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Review details

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 7cb0357d-a411-4ee3-8b24-8720bc71386d

📥 Commits

Reviewing files that changed from the base of the PR and between de8d18b and dc9a2ac.

📒 Files selected for processing (1)

• .github/workflows/relock.yml

📝 Walkthrough

Walkthrough

CI workflows now explicitly install Pixi v0.73.0 for linting, type checking, CPU tests, and GPU tests.

Changes

CI toolchain pinning

Layer / File(s)	Summary
Pin Pixi across CI jobs .github/workflows/ci.yml, .github/workflows/gpu-tests.yml	Lint, typecheck, CPU-test, and GPU-test setup steps specify Pixi v0.73.0.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Suggested reviewers: marcuscollins

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main change: pinning pixi-version in setup-pixi to make lock validation deterministic.
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.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch ci/pin-pixi-version

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[Copilot]

Pull request overview

Pins the Pixi binary version used in GitHub Actions so pixi install --locked validation is deterministic and doesn’t start failing due to upstream Pixi releases changing lockfile hashing/validation behavior.

Changes:

• Pinned pixi-version: v0.73.0 for prefix-dev/setup-pixi in the main CI workflow (all three Pixi install steps).
• Pinned pixi-version: v0.73.0 for prefix-dev/setup-pixi in the GPU test workflow.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
.github/workflows/ci.yml	Pins the Pixi binary version used across lint/typecheck/test jobs to make lock validation reproducible.
.github/workflows/gpu-tests.yml	Pins the Pixi binary version on the self-hosted GPU runner for consistent environment/lock behavior.

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[marcuscollins]

I'm curious how the relock workflow is used.