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phases/3-formula-pipeline/step0.md

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+# Step 0: formula-block-detection
+
+## Read First
+- /AGENTS.md
+- /PLAN.md
+- /PROGRESS.md
+- /docs/HARNESS.md
+- /docs/IMPLEMENTATION_PLAN.md
+- /docs/CONVERSION_POLICY.md
+- /phases/2-marker-adapter/step2.md
+
+## Task
+Implement formula candidate detection from normalized Marker blocks.
+
+Detect Marker equation blocks and text-pattern candidates while classifying inline versus block formulas based on block role and layout hints.
+
+## Sprint Contract
+- Done means: formula candidates are represented as internal objects ready for Nougat or Marker fallback.
+- Hard thresholds: ordinary currency-like dollar text is not blindly treated as math; inline/block distinction is tested; no Nougat invocation occurs yet.
+- Files owned: `src/pdftomd/formulas.py`, tests, `PROGRESS.md`, `phases/3-formula-pipeline/index.json`.
+- Dependencies: Phase 2 block normalization.
+
+## Acceptance Criteria
+```powershell
+python scripts\validate_workspace.py
+.\venv\python.exe -m pytest tests
+```
+
+## Verification
+1. Run the acceptance commands.
+2. Confirm tests include inline and block formula candidates.
+3. Update `PROGRESS.md` and this phase index.
+
+## Do Not
+- Do not call Nougat.
+- Do not render Markdown math.
+- Do not make regex the only source when structured block role exists.