Medium: [Kinetics] deriv_cryst ignores sup_sat_type and hardcodes relative supersaturation

[bernalde]

Maintainer triage (June 29, 2026)

• Status: Verified bug against the current master source in this fork.
• Severity: Medium.
• Area labels: area:kinetics, area:crystallizers.
• Tackle batch: P5 - medium-scope correctness defects.

The source review confirmed that the cited code path and failure mode are still present. The original audit details are preserved below for reproduction notes and suggested fixes.

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Original audit details

Part of the model-correctness audit — see #17.

Severity: medium | Category: logic | Location: Kinetics.py lines 948

What's wrong

deriv_cryst computes ssat = max(eps,(conc_tg-conc_sat)/conc_sat) (relative) always, but get_kinetics computes the rate with the configured sup_sat_type ('relative'/'ratio'/'absolute'). For 'absolute' or 'ratio' the analytical sensitivity is inconsistent with the rate.

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Verification: 2/2 adversarial reviewers confirmed (refuted: 0).

[bernalde]

Independent Codex verification: CONFIRMED

severity_assessment: medium
evidence: PharmaPy/Kinetics.py:946-948 always computes relative supersaturation for parameter derivatives. The actual rate path at PharmaPy/Kinetics.py:833-839 supports relative, ratio, and absolute, so sensitivities are inconsistent outside the relative case.
fix_note: Compute ssat in deriv_cryst using self.sup_sat_type.