Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In @.github/workflows/test.yml:
- Around line 131-137: Add a defensive pre-check before the "Attest test
results" step to verify the subject file exists (subject-path: source.tar.gz)
and fail with a clear message if missing; insert a small run step (e.g., in the
same job, before the actions/attest step) that tests for the presence of
source.tar.gz and exits non‑zero with a descriptive error so the attestation
step is only reached when the artifact file is actually present, ensuring
predicate-path: test-result-predicate.json is only consumed when source.tar.gz
exists.
- Around line 117-129: The predicate currently hardcodes "result": "PASSED" in
the "Generate test result predicate" step and must instead derive the result
explicitly from prior test step outcomes; update the workflow to add an
always()-run step (e.g., a step named "aggregate-test-status" or similar) that
inspects the relevant test steps' outcomes (use each test step's outcomes like
steps.<test-step-id>.outcome or the job status) and sets a build-level
output/variable (e.g., tests_result = "PASSED" or "FAILED") via GITHUB_OUTPUT,
then change the "Generate test result predicate" step to consume that output and
emit test-result-predicate.json with "result": "${{
steps.aggregate-test-status.outputs.tests_result }}" so the attestation reflects
explicit verification rather than a hardcoded value.