feat!: require an explicit fluid_name in encomp.gases (breaking)

[wlaur]

Breaking change

encomp.gases' seven public functions no longer default fluid_name to "Air", and the parameter is now keyword-only. ideal_gas_density is unaffected (it never had a default).

# before
mass_to_normal_volume(mass)
convert_gas_volume(volume, "N", condition)

# after
mass_to_normal_volume(mass, fluid_name="Air")
convert_gas_volume(volume, "N", condition, fluid_name="Air")

Affected: convert_gas_volume, mass_to_normal_volume, mass_from_normal_volume, mass_to_actual_volume, mass_from_actual_volume, actual_volume_to_normal_volume, normal_volume_to_actual_volume.

Why

This was the last implicit physical identity in the library. The same anti-pattern was already removed from encomp.coolprop.fluid (which requires name=) and convert_volume_mass (which requires a density), and AGENTS.md states the invariant — encomp.gases was the standing exception, flagged by the 1.9.2 holistic review as "an inconsistency of concept".

A guessed fluid does not fail loudly: it returns plausible numbers for the wrong gas. mass_to_normal_volume(Q(1, "kg")) silently answered for air even when the caller meant methane (a ~1.8× difference), which is precisely why the identity may not be defaulted.

Keyword-only rather than positional-with-no-default because a required parameter cannot follow the defaulted condition_* arguments — and it matches the cp.fluid(..., name=...) spelling. It also means the name can never land in a condition parameter by position.

Notes

• Released as a patch (1.9.4): per README.md, encomp does not follow strict semantic versioning, and breaking changes are called out in the release notes instead.
• AGENTS.md now records that no exceptions to the invariant remain, so the next review doesn't re-flag it.
• No docs or README examples called these functions; only the test suite needed updating, plus a new test pinning that the argument is required and keyword-only, and that naming a different gas changes the answer.

Gates

pytest 1190 passed · pyright 0 errors · pyrefly 0 errors · ty clean · ruff clean.

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