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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• CONTRIBUTING.adoc

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🔇 Additional comments (1)

CONTRIBUTING.adoc (1)

110-125: LGTM!

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📝 Summary

Summary by CodeRabbit

• Documentation
  • Added contribution guidance requiring commits to the default branch to meet the estate signing policy.
  • Explained signing requirements for people, interactive agents, apps, bots and workflows, along with the required PR merge approach.

Walkthrough

The contribution guidance adds signed-commit requirements for commits reaching the default branch. It describes signing methods for people and automated contributors, and specifies branch and merge requirements.

Changes

Signed Commit Guidance

Layer / File(s)	Summary
Signing and merge requirements CONTRIBUTING.adoc	The guidance describes signing requirements and methods, commit checks on pull request branches, squash merges, and how to replace unsigned commits. It notes that rebase-merge is disabled.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~4 minutes

Change: Other

Suggested reviewers: metadatastician

Merge Risk: ⚪ Minimal · up to 12811

This documentation-only change aligns with the cited signing policy and documented PR signature checks. No merge-blocking risk is established; the repository-specific ruleset setting remains unknown.

Security Architecture Review

Security architecture risk: 🔵 Low · up to 12811

The change documents contribution identity and merge requirements without changing executable controls. No introduced security weakness was established, but the actual signing ruleset and merge configuration could not be independently confirmed.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• inferred — The supported scope is this repository's contribution and default-branch integration policy. The changed surface does not show new credentials, expanded automation permissions, or a new cross-service execution path.

Trust Boundaries and Controls

• observed — The document places merge eligibility behind a stated signed-commit ruleset and says rebase merging is disabled. These external controls are asserted by the guidance; their active configuration and bypass permissions were not independently established.

Resilience and Maintainability Implications

• inferred — The recovery instruction retains signed commits and creates a new PR rather than prescribing a privileged bypass. It does not establish authorization, cleanup, approval handling, or concurrency behavior for interrupted or repeated recovery attempts. No automated recovery implementation is introduced, so these omissions remain limits on the assessment rather than demonstrated security failures.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: adding a Signed commits section to CONTRIBUTING.
Description check	✅ Passed	The description accurately explains the documentation change, its signing requirements, merge method, policy reference, and docs-only scope.
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,
Signed keys shine against the dark.
Squash the branch and make it neat,
Signed commits hop on steady feet.
The rabbit nibbles, pleased with the feat.}

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✨ Finishing Touches 💡 1

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