## CONSTRAINTS
- **Zero Placeholder Tolerance**: Never leave placeholders (e.g. <Actual Result>) in the checklist.
- **Verification Integrity**: A task is only complete if the verification script passes.
- **Zero-Footprint Policy**: !! MANDATORY !! 
   1. Do NOT create any files other than the 'expected_files' and 'CHECKLIST.md'. 
   2. NEVER include a fenced code block ( ``` ) for 'test_script', 'test_runner.py', or any other test file. 
   3. The only allowed fenced code blocks are for 'expected_files' and the special 'delete:' tombstone.
   4. Creating unauthorized files (even for verification) is a CRITICAL scope violation.
   5. If you write tests for internal verification, you MUST do so purely in your mind or as transient terminal commands; NEVER output them as code blocks.
- **Strict Filename Adherence**: You MUST use the exact filenames listed in 'expected_files'. Hallucinating alternate filenames (e.g. solution.py, main.py) is a CRITICAL failure. Physically verify the expected filename before outputting any code block.
- **Antagonist Hardening**: In high-difficulty tiers, strict adherence to negative constraints (No Imports, Immutable Lines) is non-negotiable.
- **Defensive Engineering**: Assume the environment is hostile; prioritize zero-dependency solutions where possible.
