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phases/2-marker-adapter/step0.md

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+# Step 0: marker-invocation-adapter
+
+## Read First
+- /AGENTS.md
+- /PLAN.md
+- /PROGRESS.md
+- /docs/HARNESS.md
+- /docs/IMPLEMENTATION_PLAN.md
+- /docs/ARCHITECTURE.md
+- /docs/TOOLCHAIN.md
+- /phases/1-core-runtime-contracts/index.json
+
+## Task
+Implement the first Marker adapter boundary that invokes Marker through a small internal interface.
+
+Keep this adapter isolated so tests can use fakes without loading large models. Real Marker invocation should be smoke-testable but not required for every unit test.
+
+## Sprint Contract
+- Done means: Marker invocation is behind a narrow interface and can return structured parse results or clear failures.
+- Hard thresholds: Marker remains the primary document parser; Nougat is not used here; unit tests avoid mandatory model downloads; parser errors are structured.
+- Files owned: `src/pdftomd/marker_adapter.py`, related tests, `PROGRESS.md`, `phases/2-marker-adapter/index.json`.
+- Dependencies: Phase 1 runtime contracts.
+
+## Acceptance Criteria
+```powershell
+python scripts\validate_workspace.py
+.\venv\python.exe -m pytest tests
+```
+
+## Verification
+1. Run the acceptance commands.
+2. Confirm the adapter can be tested without external services.
+3. Update `PROGRESS.md` and this phase index.
+
+## Do Not
+- Do not parse formulas with Nougat.
+- Do not implement Markdown rendering.
+- Do not make every test load Marker models.