add files

phases/4-semantic-enrichment/step3.md

@@ -0,0 +1,38 @@
+# Step 3: reference-indexing
+
+## Read First
+- /AGENTS.md
+- /PLAN.md
+- /PROGRESS.md
+- /docs/HARNESS.md
+- /docs/IMPLEMENTATION_PLAN.md
+- /docs/CONVERSION_POLICY.md
+- /phases/3-formula-pipeline/step3.md
+- /phases/4-semantic-enrichment/step2.md
+
+## Task
+Build a reference index for figures, tables, formulas, captions, and body references.
+
+The index should support later Markdown rendering by providing stable anchors and high-confidence link targets.
+
+## Sprint Contract
+- Done means: table, figure, and formula references can be resolved or left plain with reasons.
+- Hard thresholds: anchors are deterministic; duplicate labels are handled; missing targets do not produce broken links.
+- Files owned: `src/pdftomd/enrichment.py`, reference models/tests, `PROGRESS.md`, phase index.
+- Dependencies: Formula links and semantic block enrichment.
+
+## Acceptance Criteria
+```powershell
+python scripts\validate_workspace.py
+.\venv\python.exe -m pytest tests
+```
+
+## Verification
+1. Run the acceptance commands.
+2. Confirm figure/table/formula reference fixtures are covered.
+3. Update `PROGRESS.md` and this phase index.
+
+## Do Not
+- Do not rewrite ambiguous references.
+- Do not make anchors depend on nondeterministic ordering.
+- Do not render final Markdown here.