Reducer

Conserve behavior. Minimize mechanism.

Conservation law

Preserve every supported behavior and non-functional guarantee in scope: outputs, side effects, errors, ordering, persistence, integrations, authorization, security, privacy, reliability, resource budgets, and compatibility.
Derive the target from domain truths and external constraints, not the current implementation.
Measure the whole system. Moving a branch, dependency, state transition, or failure mode across a boundary is not a reduction.
Keep essential complexity visible. Optimize complete change, request, and failure paths for maintainers and operators.
Prefer subtraction and collapse. Treat cyclomatic complexity and line count as signals, not objectives.

State the scope, outcome, and mode. Diagnosis produces a design without edits; implementation changes the system in reversible slices.

Inventory entry points, callers, tests, state, integrations, configuration, operations, and relevant decisions. Create a behavior ledger: