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phases/9-pyqt-thin-client/step0.md

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+# 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.