From af7c81363294fe2485aeb978f7a38ac65ab8015f Mon Sep 17 00:00:00 2001
From: "Jonathan D.A. Jewell" <6759885+hyperpolymath@users.noreply.github.com>
Date: Thu, 1 Oct 2026 09:37:36 +0100
Subject: [PATCH] docs: add Signed commits section to CONTRIBUTING

Owner ruling D218. See docs/SIGNING-POLICY.adoc in hyperpolymath/standards.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WRvDivYwLSeVCJUrfjic3f
---
 CONTRIBUTING.adoc | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/CONTRIBUTING.adoc b/CONTRIBUTING.adoc
index 4c23958..11ff500 100644
--- a/CONTRIBUTING.adoc
+++ b/CONTRIBUTING.adoc
@@ -50,3 +50,20 @@ protection requires review and passing checks.
 packaging policy, secrets, licence consistency and workflow security.
 . Security issues: follow `+SECURITY.md+` — report privately, never in a
 public issue.
+
+== Signed commits
+
+Every commit that reaches the default branch must be signed; a ruleset refuses
+unsigned pushes. Estate policy:
+https://github.com/hyperpolymath/standards/blob/main/docs/SIGNING-POLICY.adoc[SIGNING-POLICY].
+
+* **People and interactive agents** sign with an SSH key registered on GitHub
+  as a *signing* key (`gpg.format=ssh`, `user.signingkey=<key>.pub`,
+  `commit.gpgsign=true`). The committer email must be verified on that account.
+* **Apps, bots and workflows** never `git push` local commits. They write
+  through the API (`createCommitOnBranch` or the estate `signed-push` action)
+  so that GitHub signs each commit.
+* Merge PRs with **squash**. The ruleset checks every commit on the PR branch,
+  not just the result, so one unsigned commit blocks the merge. Re-create such a
+  branch with signed commits (`git cherry-pick -S`) and open a new PR.
+  Rebase-merge replays commits unsigned and is disabled.