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 guidance on the signed-commit requirements for changes reaching the default branch, including signing methods for people, interactive agents, apps, bots and workflows.
  • Clarified that pull requests must be squash-merged; rebase merging is not available under the branch rules.

Walkthrough

The contribution guide now sets out signed-commit requirements for default-branch changes. It describes signing methods for people and automated contributors, and specifies squash merges and how to handle branches with unsigned commits.

Changes

Signed-commit contribution policy

Layer / File(s)	Summary
Signing instructions and merge rules CONTRIBUTING.adoc	Adds signing requirements and instructions for people, interactive agents, apps, bots and workflows. It requires squash merges, disables rebase merges and describes how to recreate branches with unsigned commits.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Other

Merge Risk: ⚪ Minimal · up to dbdac

The signing instructions name the estate-approved paths. The repository’s active merge settings could not be independently confirmed, but no concrete blocking issue was established; proceed with normal repository checks.

Security Architecture Review

Security architecture risk: 🔵 Low · up to dbdac

The change is limited to contribution guidance and does not demonstrate a new privilege grant or weakened security control. However, the claimed signed-commit enforcement and merge restrictions were not independently verified.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• inferred — The evidenced scope is repository contribution and merge procedures. The supplied change surface does not establish changed application privileges, tenant access, credential permissions, or runtime exposure.

Trust Boundaries and Controls

• observed — The text assigns local SSH signing to people and interactive agents and GitHub-produced signing to the named automation paths. It asserts unsigned-push rejection, PR-commit checks, and disabled rebase merges; those assertions are not independent proof of active controls or actor authorization.

Resilience and Maintainability Implications

• inferred — The existing instruction to enable commit.gpgsign is compatible with the new SSH configuration. It does not independently mandate GPG, so the inspected guidance does not establish conflicting signing controls.

🚥 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 directly explains the signed-commit documentation changes and their policy context.
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 marks the trail.
Squash the branch before the merge,
Signed commits pass the gate.
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