Define the focused Git commit input contract

The accepted input remains: working-tree edits to train.py and README.md in a local repo. Keep parsing and normalization in functions that do not score, train, or call a model. That split lets a test fail the boundary without blaming the core logic. The user-facing decision stays: land only the tested train.py evaluation change while README edits stay unstaged.

git check-ignore -v .env || true
git diff -- train.py README.md | head

Expected evidence: diff scoped to intended files. If the contract is silent on a bad value, later debugging will look like an algorithm bug when it is really a data bug.

Write one assertion for a neighboring valid input to the focused Git commit so tightening the boundary does not over-reject. Document field names and types the way a teammate would need them on day two of git-basics—not as comments you plan to delete.

List every field in repo with dirty train.py (eval) and README.md (docs) and mark each as required, optional, or forbidden. Required fields must fail loudly when missing; optional fields need defaults you can quote in a test; forbidden fields (secrets, raw PII, path escapes) must never be accepted silently. This list is the contract for the focused Git commit.

Add one sentence about encoding, units, or timezones if relevant to working-tree edits to train.py and README.md in a local repo. Contracts that ignore units create “correct” programs that still ship wrong decisions when someone tries to land only the tested train.py evaluation change while README edits stay unstaged.

Write the error string you want for the most likely bad input. Prefer ValueError('threshold out of range')-style messages over generic invalid input. The contract’s job is to make accidentally staging both files, or committing from the wrong directory harder to confuse with a model or algorithm bug later.

At the data contract stage for git-basics, the job is narrower than finishing a product demo. You are creating one progressive evidence piece about repo with dirty train.py (eval) and README.md (docs) that later pages inherit without redefining success. Keep that fixture small enough to inspect by hand, keep outputs copy-pasteable as text, and refuse to narrate this baseline as if it were a production SLA: git status and git diff before any add.

For this page specifically, success looks like malformed inputs rejected with field-named errors while still centering the user decision to land only the tested train.py evaluation change while README edits stay unstaged. If you cannot point to a file, command, or assertion that proves that for the focused Git commit, stay on this page instead of advancing.

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