## Prerequisite Checks (BLOCKING)

Run sequentially before any planning step:

### Prereq 1: Data Gate

1. `_docs/00_problem/acceptance_criteria.md` exists and is non-empty — **STOP if missing**
2. `_docs/00_problem/restrictions.md` exists and is non-empty — **STOP if missing**
3. `_docs/00_problem/input_data/` exists and contains at least one data file — **STOP if missing**
4. `_docs/00_problem/problem.md` exists and is non-empty — **STOP if missing**

All four are mandatory. If any is missing or empty, STOP and ask the user to provide them. If the user cannot provide the required data, planning cannot proceed — just stop.

### Prereq 2: Finalize Solution Draft

Only runs after the Data Gate passes:

1. Scan `_docs/01_solution/` for files matching `solution_draft*.md`
2. Identify the highest-numbered draft (e.g. `solution_draft06.md`)
3. **Rename** it to `_docs/01_solution/solution.md`
4. If `solution.md` already exists, ask the user whether to overwrite or keep existing
5. Verify `solution.md` is non-empty — **STOP if missing or empty**

### Prereq 3: Workspace Setup

1. Create DOCUMENT_DIR if it does not exist
2. If DOCUMENT_DIR already contains artifacts, ask user: **resume from last checkpoint or start fresh?**
