Precision and Rounding — Project-First

Purpose

Prevent accidental numeric behavior changes. The project's verified existing contract takes precedence over generic preferences. This skill does not prescribe Half-Up, Half-Even, 2 decimal places, decimal, or any global rounding mode by default.

Use with a general debugging or testing workflow; this skill is the numerical decision specialist, not a replacement for root-cause analysis or test execution.

Non-negotiable rules

1. Discover before modifying. Inspect the affected calculation end-to-end, not just the line that rounds a value. See project-discovery.md.
2. Separate facts from guesses. Cite file paths, code references, configuration and observed tests for every claim about project behavior. Search results are leads, not proof of runtime behavior.
3. Never silently change policy. No implicit switch from Half-Even to Half-Up, no automatic conversion to fixed 2dp, no change to when rounding occurs, and no broad numeric-type migration.
4. Preserve behavior by default. For bugs and improvements, change only what is required. If requested behavior conflicts with existing behavior, explicitly identify the conflict and its affected scope.
5. Do not infer an intentional policy from one incidental call. Check callers, overrides, framework defaults, docs and executable tests; multiple policies may coexist by field, operation, tenant, currency, or version.
6. Missing decision-critical evidence means stop the policy change. State the unknown and ask for the smallest needed clarification; you may still document findings or add characterization tests that do not alter production behavior.
7. No invented verification. Never claim tests passed, values were inspected, or business rules were confirmed unless actually observed.
8. No project disclosures. Never copy sensitive values or proprietary implementation into a public skill artifact. Use generic examples.