CRITICAL: Implement changelog auto-sync on develop merge

[ashleyshaw]

Summary

Currently, when PRs with CHANGELOG.md updates are merged to develop, the changelog entries are not automatically synced to the main CHANGELOG.md file. This creates a gap where merged changes aren't reflected in the changelog until manual intervention or a release.

Problem

• Changelog is validated on PR but not updated on merge
• Release workflow depends on manual changelog management
• Team loses visibility into when changes were actually merged vs. released
• Risk: changelog stale or incomplete at release time

Solution

Create new changelog-auto-update.yml workflow that:

1. Triggers when PR merges to develop with CHANGELOG.md modified
2. Extracts changelog entries from the merged PR's CHANGELOG.md
3. Appends entries to main CHANGELOG.md under [Unreleased] section
4. Validates schema before committing
5. Uses [skip ci] flag to prevent workflow loops

Implementation Details

• Effort: 2–3 hours
• Complexity: Medium
• Risk: Low (with schema validation + dry-run testing)
• Related: Changelog validation workflow (.github/workflows/changelog-validate.yml)
• Dependencies: Requires changelog schema validation script (scripts/agents/includes/changelogUtils.cjs)

Acceptance Criteria

• New workflow file created and tested in dry-run mode
• Merged PR changelog entries appear in main CHANGELOG.md within 5 minutes
• Schema validation runs before commit
• Workflow prevents duplicate entries
• All tests pass; no CI conflicts

Reference

See workflow standards audit: .github/reports/audits/workflow-standards-audit-2026-05-31.md

[linear-code]

LS-806