Add agent-approval-check composite action (#1429)

* Add agent-approval-check composite action

Require N human approvals on PRs that contain agent-authored commits.
Posts an agent-approval-check commit status that repos mark as a
required check on protected branches.

This is a sanitized port of the check Anthropic runs internally on
every agent-authored PR — same detection rules, /approve <sha>
comment flow, sibling-PR-same-SHA guard, and fail-closed semantics,
with the Anthropic-specific path exemptions and kill-switch removed
and config moved to action inputs.

Co-Authored-By: Claude <noreply@anthropic.com>

* Drop stray internal acronym from comment

* agent-approval-check: require write-access approvers, pin deps, pagination + doc fixes

🏠 Remote-Dev: homespace

* agent-approval-check: prettier

🏠 Remote-Dev: homespace

* agent-approval-check: verify approver write permission via REST; commits(last:100); docstring

🏠 Remote-Dev: homespace

* agent-approval-check: use headRefOid; drop pull_request_review trigger and correct threat-model docs

🏠 Remote-Dev: homespace

* agent-approval-check: stale-notification wording, no-retry-on-4xx, docstring API-call count

🏠 Remote-Dev: homespace

* agent-approval-check: fail-closed sibling guard on commits-ordering edge; drop stale 'reviewed' from README

🏠 Remote-Dev: homespace

* agent-approval-check: drop hardcoded API-call counts from logs; clarify author write-access requirement in README

🏠 Remote-Dev: homespace

* agent-approval-check: count all agent-email commits (close-reopen bypass); validate REQUIRED_APPROVALS>=1; exempt_head_branches warning

🏠 Remote-Dev: homespace

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Octavian Guzu <oct@anthropic.com>

agent-approval-check/agent-identities.example.yaml

@@ -0,0 +1,33 @@
+---
+# Optional config-file form of the agent-approval-check inputs.
+# Pass via `with: { config_file: .github/agent-identities.yaml }` instead of
+# the inline `agent_emails` / `agent_logins` / … inputs.
+
+# Committer emails that mark a commit as agent-authored.
+agent_emails:
+  - noreply@anthropic.com
+
+# GitHub logins treated as agents — a PR opened by, or an APPROVED review
+# from, one of these triggers the check.
+agent_app_logins:
+  - claude[bot]
+  - claude-code[bot]
+
+# Logins whose approvals never count toward the required total.
+excluded_approver_logins: []
+
+# Head-branch glob patterns that auto-pass. Leave empty: branch names are
+# attacker-controlled, so this is not a safe place to encode trust.
+exempt_head_branches: []
+
+# Per-repo path prefixes whose PRs auto-pass when ONLY those paths change.
+exempt_path_prefixes:
+  owner/repo:
+    - docs/
+
+# Per-repo base branches this check gates. A repo with no entry defaults to
+# its default branch only. Listing a repo here REPLACES that default.
+protected_bases:
+  owner/repo:
+    exact: [main]
+    prefixes: [release/]