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--- a/.github/org-rulesets/README.md
+++ b/.github/org-rulesets/README.md
@@ -0,0 +1,211 @@
+<!--
+Copyright (C) 2026 Moko Consulting <hello@mokoconsulting.tech>
+
+This file is part of a Moko Consulting project.
+
+SPDX-License-Identifier: GPL-3.0-or-later
+
+FILE INFORMATION
+DEFGROUP: GitHub.Configuration
+INGROUP: Moko-Cassiopeia.Security
+REPO: https://github.com/mokoconsulting-tech/moko-cassiopeia
+PATH: .github/org-rulesets/README.md
+VERSION: 01.00.00
+BRIEF: Documentation for organization-level repository protection rulesets
+-->
+
+# Organization-Level Repository Rulesets
+
+This directory contains JSON configuration files for GitHub organization-level repository protection rulesets. These rulesets provide centralized governance and security controls across repositories in the organization.
+
+## Overview
+
+Organization-level rulesets allow you to:
+- Define branch protection rules once and apply them across multiple repositories
+- Enforce security and compliance requirements consistently
+- Reduce manual configuration and potential errors
+- Centrally manage governance policies
+
+## Prerequisites
+
+- **Permissions Required:** Organization owner permissions
+- **GitHub Plan:** GitHub Team or Enterprise plan
+- **Feature Access:** Repository rulesets feature must be enabled for your organization
+
+## Available Rulesets
+
+### default-protection-ruleset.json
+
+**Purpose:** Provides comprehensive branch protection for main development branches.
+
+**Protected Branches:**
+- `main` (default branch)
+- `dev/**` (development branches)
+- `rc/**` (release candidate branches)
+- `version/**` (version branches)
+
+**Enforced Rules:**
+1. **Pull Request Requirements**
+   - At least 1 approving review required
+   - Dismiss stale reviews on push
+   - Require code owner review (via CODEOWNERS file)
+   - Require conversation resolution before merging
+
+2. **Status Check Requirements**
+   - `validation` - Repository structure and standards validation
+   - `quality` - PHP code quality checks (PHPStan, PHP_CodeSniffer)
+   - Strict mode enabled (branches must be up to date before merging)
+
+3. **Protection Against:**
+   - Force pushes (non-fast-forward updates)
+   - Branch deletion
+   - Non-linear history (enforces clean git history)
+   - Unsigned commits (requires commit signing)
+
+4. **Bypass Permissions**
+   - Repository administrators can bypass rules when necessary
+   - Bypass mode: always (for emergency situations)
+
+## How to Apply Organization-Level Rulesets
+
+### Method 1: GitHub Web UI
+
+1. **Navigate to Organization Settings**
+   - Go to your organization on GitHub
+   - Click **Settings** → **Repository** → **Rulesets**
+
+2. **Import Ruleset**
+   - Click **New ruleset** → **Import a ruleset**
+   - Upload the JSON file from this directory
+   - Review the configuration
+   - Click **Create** to apply
+
+3. **Configure Repository Targeting** (Optional)
+   - By default, rules apply to branches matching the patterns
+   - You can further restrict to specific repositories if needed
+
+### Method 2: GitHub API
+
+You can also apply rulesets programmatically using the GitHub REST API:
+
+```bash
+# Set your organization name and PAT
+ORG_NAME="mokoconsulting-tech"
+GITHUB_TOKEN="your_personal_access_token"
+
+# Import the ruleset
+curl -X POST \
+  -H "Accept: application/vnd.github+json" \
+  -H "Authorization: Bearer $GITHUB_TOKEN" \
+  -H "X-GitHub-Api-Version: 2022-11-28" \
+  "https://api.github.com/orgs/$ORG_NAME/rulesets" \
+  -d @.github/org-rulesets/default-protection-ruleset.json
+```
+
+### Method 3: GitHub CLI
+
+```bash
+# List existing rulesets
+gh api /orgs/mokoconsulting-tech/rulesets
+
+# Create a new ruleset
+gh api /orgs/mokoconsulting-tech/rulesets \
+  --method POST \
+  --input .github/org-rulesets/default-protection-ruleset.json
+```
+
+## Validation
+
+After applying the ruleset, validate it by:
+
+1. **Check Ruleset Status**
+   - Go to Organization Settings → Rulesets
+   - Verify the ruleset appears with "Active" status
+   - Check that target branches are correctly matched
+
+2. **Test Protection**
+   - Try to push directly to a protected branch (should fail)
+   - Try to create a PR without required checks (should be blocked)
+   - Verify status checks appear on pull requests
+
+3. **Monitor Enforcement**
+   - GitHub provides audit logs for ruleset enforcement
+   - Check Settings → Audit log to see rule triggers
+
+## Customization
+
+To customize the rulesets for your needs:
+
+1. **Edit the JSON file** with your preferred settings
+2. **Adjust branch patterns** in the `conditions.ref_name.include` array
+3. **Modify rules** in the `rules` array as needed
+4. **Update bypass actors** to match your organization structure
+
+### Common Customizations
+
+**Change required approvals:**
+```json
+"required_approving_review_count": 2
+```
+
+**Add more status checks:**
+```json
+"required_status_checks": [
+  { "context": "validation", "integration_id": null },
+  { "context": "quality", "integration_id": null },
+  { "context": "security-scan", "integration_id": null }
+]
+```
+
+**Relax commit signing requirement:**
+Remove or comment out the `required_signatures` rule.
+
+## Monitoring and Maintenance
+
+- **Regular Reviews:** Review rulesets quarterly to ensure they align with current practices
+- **Updates:** When updating rulesets, use the GitHub UI or API to update existing configurations
+- **Audit Logs:** Monitor organization audit logs for bypass usage and rule violations
+- **Team Communication:** Inform team members when rulesets change
+
+## Troubleshooting
+
+### Ruleset Not Applying
+
+- Verify you have organization owner permissions
+- Check that the organization has the appropriate GitHub plan
+- Ensure branch patterns match your actual branch names
+- Review enforcement status (should be "active")
+
+### Status Checks Failing
+
+- Verify workflow names match the required status check contexts
+- Check that workflows are configured to run on protected branches
+- Ensure workflows have appropriate permissions
+
+### Bypass Not Working
+
+- Verify actor_id matches your organization's role IDs
+- Check bypass_mode is set correctly
+- Review user/team permissions in organization settings
+
+## References
+
+- [GitHub Docs: Creating rulesets for repositories in your organization](https://docs.github.com/en/organizations/managing-organization-settings/creating-rulesets-for-repositories-in-your-organization)
+- [GitHub Docs: Managing rulesets for repositories in your organization](https://docs.github.com/en/organizations/managing-organization-settings/managing-rulesets-for-repositories-in-your-organization)
+- [GitHub Ruleset Recipes](https://github.com/github/ruleset-recipes)
+- [GitHub REST API: Rulesets](https://docs.github.com/en/rest/orgs/rules)
+
+## Metadata
+
+* **Directory:** .github/org-rulesets/
+* **Repository:** https://github.com/mokoconsulting-tech/moko-cassiopeia
+* **Maintainer:** Moko Consulting Engineering
+* **Version:** 01.00.00
+* **Status:** Active
+* **Last Updated:** 2026-01-11
+
+## Revision History
+
+| Date       | Change Summary                                              | Author          |
+| ---------- | ----------------------------------------------------------- | --------------- |
+| 2026-01-11 | Initial creation of organization-level ruleset configuration | Moko Consulting |
--- a/.github/org-rulesets/default-protection-ruleset.json
+++ b/.github/org-rulesets/default-protection-ruleset.json
@@ -0,0 +1,69 @@
+{
+  "name": "Moko Cassiopeia - Default Branch Protection",
+  "description": "Organization-level protection for main development branches with required status checks and review requirements",
+  "target": "branch",
+  "enforcement": "active",
+  "conditions": {
+    "ref_name": {
+      "include": [
+        "~DEFAULT_BRANCH",
+        "refs/heads/main",
+        "refs/heads/dev/**",
+        "refs/heads/rc/**",
+        "refs/heads/version/**"
+      ],
+      "exclude": []
+    }
+  },
+  "rules": [
+    {
+      "type": "pull_request",
+      "parameters": {
+        "required_approving_review_count": 1,
+        "dismiss_stale_reviews_on_push": true,
+        "require_code_owner_review": true,
+        "require_last_push_approval": false,
+        "required_review_thread_resolution": true
+      }
+    },
+    {
+      "type": "required_status_checks",
+      "parameters": {
+        "strict_required_status_checks_policy": true,
+        "required_status_checks": [
+          {
+            "context": "validation",
+            "integration_id": null
+          },
+          {
+            "context": "quality",
+            "integration_id": null
+          }
+        ]
+      }
+    },
+    {
+      "type": "non_fast_forward",
+      "parameters": {}
+    },
+    {
+      "type": "deletion",
+      "parameters": {}
+    },
+    {
+      "type": "required_linear_history",
+      "parameters": {}
+    },
+    {
+      "type": "required_signatures",
+      "parameters": {}
+    }
+  ],
+  "bypass_actors": [
+    {
+      "actor_id": 5,
+      "actor_type": "RepositoryRole",
+      "bypass_mode": "always"
+    }
+  ]
+}
--- a/GOVERNANCE.md
+++ b/GOVERNANCE.md
@@ -73,6 +73,17 @@ Significant changes should:
 * Consider backward compatibility and upgrade impact.
 * Include documentation updates when behavior or usage changes.

+### Repository Protection
+
+The project enforces technical governance controls through organization-level repository rulesets:
+
+* **Branch protection** for main development branches with required reviews and status checks
+* **Commit signing** requirements to ensure authenticity
+* **Linear history** enforcement to maintain clean git logs
+* **Deletion protection** to prevent accidental branch removal
+
+Configuration and implementation details are maintained in `.github/org-rulesets/`.
+
 ## Release Authority

 Only maintainers may:
--- a/SECURITY.md
+++ b/SECURITY.md
@@ -127,6 +127,17 @@ The project aims to manage supply chain risk through:

 If you identify a supply chain issue (for example compromised action, dependency confusion, or malicious upstream artifact), report it as a vulnerability.

+## Repository Protection and Access Controls
+
+The project uses organization-level repository rulesets to enforce security and governance policies:
+
+* **Branch Protection:** Main development branches (`main`, `dev/**`, `rc/**`, `version/**`) are protected with required reviews and status checks.
+* **Required Status Checks:** All changes must pass validation and quality checks before merging.
+* **Commit Signing:** Commits must be signed to verify author identity and prevent tampering.
+* **Code Review:** At least one approving review is required, including code owner approval.
+
+Configuration files for organization-level rulesets are maintained in `.github/org-rulesets/`. See the README in that directory for implementation details.
+
 ## Secure Development and CI Expectations

 Security posture is reinforced through operational controls: