feat(attest): add attest-release-files reusable for python-release

[CybotTM]

Merging adds a new reusable attest-release-files.yml that records SLSA build provenance for the files a python-release.yml run attached to its GitHub Release, called as a second job with needs: release. Existing python-release.yml callers are unaffected; only callers that opt in grant id-token: write + attestations: write on the new job.

Fixes #417

Why a paired reusable instead of an attest input on python-release.yml

The issue proposes an attest: true input that attests inside the github-release job, before the release is created. That design cannot be made non-breaking. actions/attest-build-provenance requires attestations: write, and a called workflow's job permissions are validated statically at startup, before any job-level if: is evaluated. This repo already documents and designs around that rule: the attest-image.yml header, the sbom job comment in build-container-bake.yml, rule 1 in docs/reusable-workflow-permissions.md, and #265. A job permission cannot be conditional either, so declaring attestations: write on github-release, or on any separate job inside python-release.yml even when it is skipped, would turn the next tag push of both current callers into startup_failure. Both of them grant exactly contents: write + id-token: write: herdr-bg-activity release.yml and coding_agent_cli_toolset release.yml. Neither is template-managed (no templates/ file calls python-release.yml), so no drift sync would roll the new grant out.

The two options considered and rejected:

• Input plus required attestations: write for all callers, the build-container.yml model ("required even when attest=false"). It attests before publishing, but it breaks every caller until each one is edited by hand.
• A github-release job with no permissions: block, so it inherits the caller's ceiling and an if: inputs.attest step works without a new required scope. It drops the explicit least-privilege declaration that the workflow's SECURITY header and the permissions doc treat as convention.

Trade-off accepted: the attestation is recorded seconds after the Release is public, not before, which is the same window herdr-bg-activity has today. What the issue asked to remove, the hand-written job with duplicated pinned SHAs in the caller, is removed. If you prefer attesting before publishing and are willing to edit both callers, the input variant is a small follow-up on top of this.

Changes

• .github/workflows/attest-release-files.yml (new): inputs subject-path (required; same value as release-files) and artifact-name (default dist). It has one job with id-token: write + attestations: write, harden-runner, actions/download-artifact pinned to the SHA python-release.yml uses, and actions/attest-build-provenance@4d101475… # v4.2.2, which is the SHA used everywhere else in this repo and the current latest release. subject-path reaches the shell only through env: and is word-split with globbing disabled, then each pattern is expanded separately. An empty or whitespace-only input fails with No subject-path, and a pattern that matches nothing fails with No subject files and names that pattern. Every pattern is checked, not only the first. The resolved list is passed to the action via with:. The file has a CALLER REQUIREMENTS block and a "why separate" header matching attest-image.yml.
• .github/workflows/python-release.yml: comment-only. It adds a caller pattern for the pairing and a note on why provenance is not an input here. The jobs, inputs and permissions are unchanged.
• docs/reusable-workflow-permissions.md: new contract row for attest-release-files.yml.

Consumer follow-up

After merge, netresearch/herdr-bg-activity can replace its hand-written attest job with uses: netresearch/.github/.github/workflows/attest-release-files.yml@main and subject-path: 'dist/*.tar.gz dist/SHA256SUMS.txt' (or 'dist/*'), keeping the same id-token: write + attestations: write grant. That repo is not touched here.

Verification

• actionlint (both workflows): clean. It includes shellcheck on run blocks, and shellcheck -s bash on the extracted resolve script is also clean.
• zizmor 1.30.1 --config .github/zizmor.yml: no findings. The 3 suppressed findings are the 2 already on base python-release.yml plus 1 in the new file.
• yamllint with the lint-yaml.yml inline defaults: clean.
• markdownlint-cli2 on the doc: 0 issues.
• The resolve step was extracted with yq and run against a scratch dist/. Empty input, whitespace-only input, a non-matching pattern and one non-matching pattern out of two all exit 1 with the named error. dist/* and a two-pattern list resolve to the expected files. 'dist/*; touch PWNED $(touch PWNED2)' fails on the literal pattern and creates no files.
• Not run end-to-end on a real tag. The job shape matches herdr-bg-activity's existing attest job, which produced verifiable v0.1.0 attestations with the same permissions and the same download-then-attest steps.

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• .github/workflows/attest-release-files.yml

📝 Walkthrough

Walkthrough

The pull request adds a reusable attest-release-files.yml workflow. It accepts subject and artifact inputs, downloads the artifact, validates and resolves subject paths, and creates Sigstore-backed SLSA provenance. It also adds caller documentation and records the required permissions.

Estimated code review effort

Priority: ➖ Normal

Change: Feature · Severity of issue fixed: Medium

Merge Risk: 🟡 Moderate · up to 9af4f

Unsafe subject patterns can attest files that were not release artifacts, undermining provenance integrity. Constrain subjects to regular files under dist before merging.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the main change: adding a reusable workflow for release-file attestations in the Python release process.
Description check	✅ Passed	The description is detailed and covers the change, rationale, issue reference, consumer follow-up, permissions, implementation details, and verification. It does not use the template's Type of Change …
Linked Issues check	✅ Passed	The changes address the coding objective in issue #417. The new reusable .github/workflows/attest-release-files.yml downloads the dist artifact, rejects an empty subject-path, rejects patterns w…
Out of Scope Changes check	✅ Passed	The changed files stay within issue #417. The new reusable workflow implements release-file attestation. The additions to python-release.yml and docs/reusable-workflow-permissions.md document its …
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…

✨ Finishing Touches 💡 1

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• Commit unit tests in branch feat/python-release-attest

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch feat/python-release-attest

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Inline comments:
In @.github/workflows/attest-release-files.yml:
- Line 127: Update the subject-path resolution logic around the matches[0] check
to canonicalize each resolved match, verify it is a regular file, and ensure its
canonical path is contained under the canonical dist directory before appending
it to FILES. Reject absolute, traversal, directory, and other out-of-tree
matches while preserving the existing handling for valid dist files.

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Configuration used: Organization UI

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• .github/workflows/attest-release-files.yml
• .github/workflows/python-release.yml
• docs/reusable-workflow-permissions.md

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[CybotTM]

Self-review: bdb248b

The review this pull request demands is unsatisfiable (Copilot quota wall or repeated bot failures on this head). Per the documented fallback, the diff on this head was reviewed by the PR author; this comment is the on-the-record attestation the merge gate reads back. It stops matching on the next push.