Domain-specific physical constraints (absolute zero, non-negative frequency, etc.) not enforced

[matt-edmondson]

Summary

CLAUDE.md lists the following invariants as part of the project's validation rules:

• Temperature values cannot be below absolute zero (0 K)
• Frequency values cannot be negative
• Throw DivideByZeroException when dividing by zero in DivideToStorage

None of these are enforced in the current generated quantity types.

Evidence

Semantics.Quantities/Generated/.../Temperature.g.cs accepts any value via Create/From*. No < 0 K guard.

grep -E "absolute zero|cannot be negative" Semantics.Quantities/Generated/**/*.g.cs returns nothing.

Semantics.Quantities/PhysicalQuantity.cs does not implement per-dimension validation hooks.

Suggested next step

Extend dimensions.json (or a sibling metadata file) with optional physicalConstraints per dimension (e.g. { "minValue": "0", "minValueUnit": "Kelvin" }) and have the generator emit factory-level guards that throw ArgumentException when violated. Cover with tests for at minimum: Temperature absolute zero, Frequency >= 0, Wavelength > 0, Mass > 0, Pressure (absolute) >= 0.

Area / Severity

SourceGenerators / Metadata · incomplete

[matt-edmondson]

Partially resolved. With the V0 non-negativity invariant from #50 most of this issue's listed constraints are now enforced structurally — Temperature, Frequency, Wavelength, Mass, AbsolutePressure are all V0 dimensions, so their factories already throw ArgumentException on a negative input. CLAUDE.md was updated in #70 to call this out explicitly.

DivideByZero is enforced in SemanticQuantity.DivideToStorage and the / operator (Semantics.Quantities/SemanticQuantity.cs:122-128, 198).

What's still open:

1. Strict-positive (> 0) vs non-negative (>= 0). Wavelength = 0 m and Mass = 0 kg are unphysical but currently allowed because V0 only floors at 0. If we want to enforce the stricter rule, add an optional physicalConstraints: { minExclusive: "0" } to the dimension entry and emit a stricter guard from a new Vector0Guards.EnsurePositive.
2. Upper bounds and non-zero floors that don't match the V0 default. None are needed today; the metadata field above plus a maxInclusive would cover them when the need shows up.
3. Non-Kelvin temperature inputs. Temperature.FromCelsius(-300) and Temperature.FromFahrenheit(-500) should throw because they map to negative Kelvin. This is currently moot because QuantitiesGenerator emits a factory for only the first availableUnit #48 hasn't been done yet (only FromKelvin exists). When the per-unit factories from QuantitiesGenerator emits a factory for only the first availableUnit #48 land, the conversion-then-guard order in Vector0Guards.EnsureNonNegative will catch it automatically.

Tracking continues here; recommend leaving open until #48 is done and we can decide whether to add the physicalConstraints schema.

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