Day Code

Get the code and tests ready for a given day of the deep-roots curriculum.

## Steps

1. Read `README.md` to find the deliverable for the requested day (the "Deliverable" column in the week table).

2. Read `NOTES_TEMPLATE.md` to understand the day's context.

3. Check the day folder (`weekN/dayNN-<topic>/`) to see what already exists. If implementation and test files are already there, run the tests first — only write code if tests are failing or missing.

4. Read any existing notes.md in the folder to understand intent. Read the previous day's implementation file for style and naming conventions.

5. Create or fix the implementation file and test file following the conventions from existing days:
   - Implementation file: tutorial-style, run top-to-bottom with `python <file>.py`, thorough inline comments explaining the *why* not just the *what*
   - Test file: pytest functions, each comparing against PyTorch ground truth using a `check(label, passed)` helper, runnable standalone with `if __name__ == '__main__'`
   - No `nn.Module` or high-level abstractions unless the day explicitly introduces them

6. Run the tests with `uv run pytest weekN/dayNN-.../test_*.py -v` and iterate until all pass.

7. Run the main script with `uv run python weekN/dayNN-.../\*.py` and confirm it runs cleanly to completion.

Report: which files were created or changed, test results, and any gotchas encountered.

## Usage

/day-code 4