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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ℹ️ Recent review info

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Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Advanced

Run ID: 080b1c65-ef86-4002-be38-31fcb1b94c11

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Reviewing files that changed from the base of the PR and between d97ecaa and 99aff60.

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• .github/CONTRIBUTING.md

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🔇 Additional comments (1)

.github/CONTRIBUTING.md (1)

209-209: 🎯 Functional Correctness

The requirement to open a new pull request cannot be decided from the available evidence. .github/CONTRIBUTING.md:209 instructs contributors to create a new pull request, but the applicable D218 or estate rule was not located. GitHub’s documented workflow supports force-pushing the corrected branch, but it does not establish whether the estate imposes an additional requirement.

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📝 Summary

Summary by CodeRabbit

• Documentation
  • Updated contribution guidance to clarify that commits reaching the default branch must be signed and that pull requests require squash merges.
  • Added instructions for handling branches containing unsigned commits.

Walkthrough

The contribution guide now describes default-branch commit-signing rules, signing methods for different contributors, and pull request branch and merge requirements.

Changes

Commit-signing guidance

Layer / File(s)	Summary
Signing and merge requirements .github/CONTRIBUTING.md	The guide requires signed commits for the default branch and specifies signing methods for people, interactive agents, apps, bots and workflows. It also requires squash merges, directs contributors to recreate unsigned branches with signed commits, and states that rebase-merge is disabled.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~8 minutes

Change: Other

Merge Risk: ⚪ Minimal · up to 99aff

The guide follows the prescribed signed-commit recovery workflow. No supported merge-blocking issue remains.

Architecture Summary

Architecture risk: 🔵 Low · up to 99aff

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: The previous general signing-key instructions, git log --show-signature verification command and re-sign request are replaced with default-branch ruleset requirements. People and interactive agents must use a registered GitHub SSH signing key and verified committer email; apps, bots and workflows must create commits through the API or estate action. PRs must be squash-merged because every branch commit is checked; unsigned branches must be recreated with signed commits, and rebase-merge is disabled.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the documentation change and the addition of the Signed commits section to CONTRIBUTING.
Description check	✅ Passed	The description is directly related to the documentation changes. It explains the signed-commit policy, contributor requirements, merge method, and scope of the change.
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 signs each commit with care,
Then checks the branch before it’s there.
A squash merge keeps the history neat,
Signed commits make the rules complete.
The rabbit hops, content with the feat.}

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