Module conserved 

Conservation, as a thing a process must answer for rather than a property it is trusted to have.

SurfaceOptics stores reflectance and transmittance and computes absorptance as the remainder, so a surface cannot return more light than reached it. That is the right idea and the wrong scope: it protects one quantity at one kind of boundary. Momentum in a collision, charge across a junction, mass through a pipe and energy across a coupling interface are all the same problem, and all of them are places a simulation can quietly manufacture something.

So a process reports what it holds, before and after, and the difference is checked. A Ledger is that report; audit is that check; a Violation names what went missing and where.

Relative to what, exactly

Floating-point arithmetic loses the low bits of every sum, so no real integrator conserves anything exactly and a test for exact equality would fail on correct code. The loss is bounded and relative — but relative to the wrong thing if one is not careful, and this is the trap:

A well-formed system’s conserved total is often exactly zero. One domain holds a debt of 28.9 J and another holds 28.9 J of asset, and the sum is nothing. Comparing the residual against that sum makes every rounding error a 100% relative error, and the audit fires on correct code.

So a Ledger entry records the largest magnitude that went into it as well as the total, and audit judges the change against that. Rounding error scales with the size of the numbers being added, not with the size of their sum, and this is the version of the tolerance that says so.

Modules

quantity

The quantities worth naming. Strings rather than an enum, so a domain crate can add its own without editing the kernel — but these spellings are the ones audit will match across domains, so use them.

Structs

Ledger

What a process claims to be holding, by quantity name, in SI base units.

Tolerances

Compare two ledgers and name the first quantity that moved by more than rel_tol, in the fixed order the ledger keeps its names.

Violation

A conservation law that did not hold.

Traits

Conserves

Something that can say what it is holding. Implemented by domains, and by anything else whose books are worth checking.

Functions

audit

Audit with one tolerance for every quantity.

audit_with

Audit with a tolerance per quantity.