docs: add Signed commits section to CONTRIBUTING

[hyperpolymath]

Adds a Signed commits section to this repo's CONTRIBUTING, per owner ruling D218. The estate policy is docs/SIGNING-POLICY.adoc in hyperpolymath/standards.

This repo's default branch is covered by the zero-bypass Require-Signed-Commits ruleset, and rebase-merge is off. The section tells contributors what that requires:

• People and interactive agents sign with an SSH signing key.
• Apps, bots and workflows write through the API, so GitHub signs their commits.
• PRs are merged with squash.

If the file already had its own signing section, that section is replaced in place instead of adding a second one. Lines elsewhere that told people to sign with GPG are changed to match the policy (SSH for people).

This is a docs-only change. The commit was created through createCommitOnBranch, so GitHub signs it.

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Reviewing files that changed from the base of the PR and between 9ba5da2 and 7ac2023.

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• .github/CONTRIBUTING.md

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🔇 Additional comments (1)

.github/CONTRIBUTING.md (1)

123-138: LGTM!

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📝 Summary

Summary by CodeRabbit

• Documentation
  • Added guidance requiring signed commits for changes merged into the default branch, including setup instructions and supported commit workflows. Unsigned commits block merging, and rebase merges are unavailable.

Walkthrough

The contribution guide now requires signed commits to reach the default branch. It gives signing and commit-submission instructions for people, interactive agents, apps, bots and workflows, and describes the merge methods and restrictions.

Changes

Signed Commit Policy

Layer / File(s)	Summary
Commit signing and merge guidance .github/CONTRIBUTING.md	The guide specifies signing requirements and methods, API-based commit creation for apps, bots and workflows, squash merges, and restrictions on unsigned commits and rebase merges.

Priority: ⬇️ Low

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

Change: Other

Suggested reviewers: metadatastician

Merge Risk: ⚪ Minimal · up to 7ac20

The signing and squash guidance is supported by the repository’s active signature requirement. No established issue blocks this documentation change; the rebase-merge setting remains unconfirmed.

Architecture Summary

Architecture risk: 🔵 Low · up to 7ac20

The changed surface does not map to a changed system, dependency edge, entrypoint, or external dependency.

Changed systems: None identified.

Architecture concerns
No architecture-level concerns identified.

Review details

Before / after behavior

• observed — Modified behavior in .github/CONTRIBUTING.md: Adds signed-commit requirements and instructions: people and interactive agents use a registered GitHub SSH signing key and verified committer email; apps, bots and workflows submit commits through the API rather than pushing local commits. It directs contributors to squash-merge, states that unsigned PR-branch commits block merging, and notes that rebase-merge is disabled because replayed commits are unsigned.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main documentation change: adding a Signed commits section to CONTRIBUTING.
Description check	✅ Passed	The description directly explains the signed-commits documentation, the signing policy, and the related contributor guidance.
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…
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.

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_{A rabbit checks each commit’s mark
SSH keys sign before the push
Bots send commits through API
Squash merges keep the branch in line
Signed hops reach the default branch}

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✨ Finishing Touches 💡 1

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