# Step 3: chunk-renderer

## Read First
- /AGENTS.md
- /PLAN.md
- /PROGRESS.md
- /docs/HARNESS.md
- /docs/IMPLEMENTATION_PLAN.md
- /docs/ARCHITECTURE.md
- /docs/CONVERSION_POLICY.md
- /phases/1-core-runtime-contracts/step2.md
- /phases/5-markdown-rendering-assets/step2.md

## Task
Implement chunk planning and chunk Markdown bundle writing over enriched blocks.

Chunk boundaries should target 20 pages but preserve logical block integrity for paragraphs, tables, figures, and formulas.

## Sprint Contract
- Done means: chunk files with frontmatter can be written deterministically from internal document fixtures.
- Hard thresholds: block integrity is preserved at chunk boundaries; chunk frontmatter includes minimum context; quality gates run on rendered chunks.
- Files owned: `src/pdftomd/chunking.py`, `src/pdftomd/renderer.py`, tests, `PROGRESS.md`, phase index.
- Dependencies: Renderer, assets, and output bundle contracts.

## Acceptance Criteria
```powershell
python scripts\validate_workspace.py
.\venv\python.exe -m pytest tests
```

## Verification
1. Run the acceptance commands.
2. Confirm long-document chunk fixtures cover boundary behavior.
3. Update `PROGRESS.md` and this phase index.

## Do Not
- Do not split blocks in the middle to satisfy exact 20-page counts.
- Do not create document sidecar metadata files.
- Do not implement CLI orchestration here.