Synthetic plan.md fixture with source_findings: block-style YAML list of 3
40-char hex IDs in frontmatter, plus minimal plan structure (Title +
Implementation Plan + 1 Step + Manifest). 3 tests verify:
1. plan-validator accepts a plan with source_findings (additive optional field)
2. frontmatter parser extracts source_findings as array of strings
3. each ID matches the 40-char lowercase hex format from finding-id.mjs
Closes the SC3(b) gap flagged by adversarial review (scope-guardian Gap 2).
LLM-level behavior (planner emitting source_findings) remains non-testable
without live invocation; this covers the structural contract.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
