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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• .github/CONTRIBUTING.md

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🔇 Additional comments (1)

.github/CONTRIBUTING.md (1)

89-105: LGTM!

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📝 Summary

Summary by CodeRabbit

• Documentation
  • Added guidance on commit signing, including requirements for pull request branches and the default branch.
  • Clarified how people, interactive agents, apps, bots and workflows should create signed commits, and which merge strategies are supported.

Walkthrough

The contribution guide now documents signed-commit requirements for commits reaching the default branch. It gives signing and commit-creation instructions for people and automated workflows, and explains the required merge method and handling of unsigned pull request branch commits.

Changes

Signed Commit Guidance

Layer / File(s)	Summary
Commit signing instructions .github/CONTRIBUTING.md	Adds signing requirements, SSH signing-key and verified committer-email guidance, commit procedures for people and automated workflows, squash-merge instructions, and steps for unsigned pull request branch commits.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~3 minutes

Change: Other

Merge Risk: ⚪ Minimal · up to 8a4d0

The guide directs people to SSH signing and automation to API-based or estate-action commits, followed by squash merging. No conflicting checked-in instruction or actionable merge blocker was established; GitHub-specific behavior remains outside the available repository evidence.

Architecture Summary

Architecture risk: 🔵 Low · up to 8a4d0

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 procedures for people, agents, apps, bots, workflows and PRs, including the SSH signing configuration, API-based commit creation, squash-merge requirement, and handling of unsigned branch commits.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the documentation change: adding a Signed commits section to CONTRIBUTING.
Description check	✅ Passed	The description directly explains the documentation update, its signing-policy requirements, and its scope as a docs-only 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,
An SSH key is ready there.
The bots use APIs to write,
Then squash the branch before its flight.
Unsigned commits take a signed new track,
And hop to a pull request back.}

_{Comment @coderabbitai help to get the list of available commands.}

✨ Finishing Touches 💡 1

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