# Step 0: ui-api-contract

## Read First
- /AGENTS.md
- /PLAN.md
- /PROGRESS.md
- /docs/HARNESS.md
- /docs/IMPLEMENTATION_PLAN.md
- /docs/UI_GUIDE.md
- /docs/ARCHITECTURE.md
- /phases/8-release-docs-packaging/index.json

## Task
Define the stable core API contract that PyQt will call.

This step should verify that the UI does not need to import Marker, Nougat, PyMuPDF, or renderer internals directly.

## Sprint Contract
- Done means: UI-facing API functions/classes are documented and tested without building UI screens.
- Hard thresholds: UI remains a thin client; conversion logic is not duplicated; progress/resume events are available through the API.
- Files owned: `src/pdftomd/`, `tests/`, `docs/UI_GUIDE.md`, `PROGRESS.md`, `phases/9-pyqt-thin-client/index.json`.
- Dependencies: Local MVP release-ready CLI/library.

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

## Verification
1. Run the acceptance commands.
2. Confirm UI boundary in `docs/UI_GUIDE.md` remains accurate.
3. Update `PROGRESS.md` and this phase index.

## Do Not
- Do not create UI widgets yet.
- Do not import parser internals in UI-facing code.
- Do not change CLI behavior unless tests require it.