Fix release docs reviewer routing

[danbarr]

Description

Fixes reviewer-routing regressions introduced by #1111 and exposed by #1120, without adding a PAT or organization-membership permission.

The workflow now treats GitHub's review-request response as the repository-access check and fails closed when GitHub cannot provide a reliable decision:

• The release owner is always assigned and requested as a reviewer, including when their own commits are classified as non-docs-facing.
• Each docs-facing contributor is requested directly. If GitHub specifically rejects the request because the contributor lacks repository access, the workflow maps every relevant full commit SHA to its merged upstream PR and requests the human merger as a stand-in.
• Rate limits, server errors, malformed responses, and transport failures stop reviewer routing instead of being mistaken for access rejection.
• A rejected docs-facing owner follows the same merger stand-in path as any other docs-facing contributor.
• If no eligible stand-in can be requested, the PR body provides an explicit manual-routing action without @-mentioning the upstream contributor.
• An unresolved release owner is counted as a routing issue so the PR cannot report that no action is required.
• Non-docs-facing contributors are counted without being individually named or notified because they have no review action.
• A missing, incomplete, invalid, or duplicate contributor classification in REVIEWERS.json falls back to requesting every release contributor.

Reviewer assignment now lives in a focused Python helper instead of inline workflow Bash. Regression tests cover access rejection versus operational API failure, unconditional owner review, docs-facing owner fallback, missing and invalid classification fallbacks, conflicting duplicate classifications, multiple docs-facing PRs, stand-in deduplication, non-docs-facing counts, unresolved owner handling, and unresolved stand-in routing.

Type of change

• Bug fix (typo, broken link, etc.)

Related issues/PRs

• Follow-up to Assign a release owner to autogen-docs PRs #1111
• Observed in Update stacklok/toolhive to v0.45.0 #1120

Testing

• python3 -m unittest discover -s .github/scripts -p 'test_*.py'
• actionlint .github/workflows/upstream-release-docs.yml .github/workflows/_static-checks.yaml
• zizmor .github/workflows/upstream-release-docs.yml .github/workflows/_static-checks.yaml
• npm run prettier
• npm run eslint
• npm run build

Submitter checklist

Content and formatting

• I have reviewed the content for technical accuracy
• I have reviewed the content for spelling, grammar, and style

Reviewer checklist

Content

• I have reviewed the content for technical accuracy
• I have reviewed the content for spelling, grammar, and style

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Project	Deployment	Actions	Updated (UTC)
docs-website	Ready	Preview	Aug 28, 2026 2:41pm

[Copilot]

Pull request overview

This PR updates the .github/workflows/upstream-release-docs.yml reviewer assignment logic to avoid pinging external (non-collaborator) contributors for “no docs impact” commits, and to add a stand-in reviewer fallback when GitHub rejects review requests for non-collaborator docs-facing contributors.

Changes:

• Restricts “No docs impact identified” @-mentions to docs-website collaborators; counts external contributors without mentioning them.
• Adds stand-in reviewer resolution by finding the merger of the upstream PR containing a contributor’s first commit, and requests review from that merger when the contributor can’t be assigned.
• Extends PR-body augmentation to include stand-in explanations and separate member vs external FYI counts.

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[Copilot]

Pull request overview

Copilot reviewed 5 out of 6 changed files in this pull request and generated 3 comments.

[jhrozek]

LGTM overall. I found a few routing edge cases worth addressing before this workflow becomes the source of truth for review assignment.

[danbarr]

@jhrozek thanks for the review! I've addressed the items you pointed out.