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phases/5-markdown-rendering-assets/step0.md

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+# Step 0: markdown-block-renderer
+
+## Read First
+- /AGENTS.md
+- /PLAN.md
+- /PROGRESS.md
+- /docs/HARNESS.md
+- /docs/IMPLEMENTATION_PLAN.md
+- /docs/ARCHITECTURE.md
+- /docs/CONVERSION_POLICY.md
+- /phases/4-semantic-enrichment/index.json
+
+## Task
+Implement block-level Markdown rendering for headings, paragraphs, lists, blockquotes, formulas, captions, and simple references.
+
+Renderer tests should use internal block fixtures, not live PDF parsing.
+
+## Sprint Contract
+- Done means: core block types render to deterministic Markdown strings with focused tests.
+- Hard thresholds: math delimiter validation is applied; renderer does not inject warnings/errors into Markdown; output is stable across runs.
+- Files owned: `src/pdftomd/renderer.py`, tests, `PROGRESS.md`, `phases/5-markdown-rendering-assets/index.json`.
+- Dependencies: Phase 4 enriched blocks and Phase 3 formula outputs.
+
+## Acceptance Criteria
+```powershell
+python scripts\validate_workspace.py
+.\venv\python.exe -m pytest tests
+```
+
+## Verification
+1. Run the acceptance commands.
+2. Confirm renderer tests are focused, not full snapshots.
+3. Update `PROGRESS.md` and this phase index.
+
+## Do Not
+- Do not invoke Marker or Nougat.
+- Do not implement table/asset file writing in this step.
+- Do not add sidecar document outputs.