## 1. Implementation
- [x] Omit empty/self artifact link fields from rendered artifact frontmatter.
- [x] Ensure transcript, assistant context, and summary frontmatter include only other run artifacts.

## 2. Verification
- [x] Add/update artifact frontmatter behavior tests.
- [x] Run focused artifact/summary tests.
- [x] Run `openspec validate remove-artifact-self-frontmatter-links --strict`.