Use artifacts to share Maven dependencies between workflow jobs

[Copilot]

GitHub Actions cache is only restored at job start and saved at job end—not shared between jobs in the same workflow run. The parallel test jobs were redundantly downloading Maven dependencies already fetched by the build job.

Changes

Build job:

• Uploads .m2-cache as artifact after make install
• Retains cache action for cross-run optimization (restores from previous workflow runs)

Test jobs (modern-tests, legacy-tests):

• Download maven-dependencies-cache artifact from build job
• Removed redundant cache actions—artifacts provide dependencies directly

Configuration:

• Artifact name: maven-dependencies-cache (specific to avoid conflicts)
• Retention: 7 days (allows debugging and re-runs)

Result

Dependencies downloaded once per workflow run instead of three times. Cache provides cross-run optimization, artifacts provide within-run sharing.

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Summary by cubic

Applied feedback from #1792 to share Maven dependencies via artifacts and stabilize modern and legacy test jobs, improving reliability in CI and local development.

• Bug Fixes
  • Workflow: upload Maven cache artifact in the build job (7-day retention, specific name); download it in modern-tests and legacy-tests; removed redundant cache steps in parallel jobs.
  • Devcontainer: ensured build steps match CI to prevent postCreate/startup issues.

^{Written for commit cd8fc42. Summary will update on new commits.}

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[cubic-dev-ai]

No issues found across 1 file

Confidence score: 5/5

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[Copilot]

Pull request overview

This PR optimizes the GitHub Actions workflow by eliminating redundant Maven dependency downloads across parallel test jobs. GitHub Actions cache is only available at job boundaries, not shared between jobs in the same workflow run, causing the build, modern-tests, and legacy-tests jobs to each download dependencies independently.

Changes:

• Build job uploads Maven dependencies as an artifact after compilation
• Modern-tests and legacy-tests jobs download the shared artifact instead of re-fetching dependencies
• Cache action retained in build job for cross-run optimization only