Audit-First Haemodynamic Navier-Stokes CFD I: 2D Steady Flow on Synthetic Vascular Geometry (Reproducibility Contract)

This record presents an audit-first haemodynamic Navier-Stokes CFD protocol for Route A in a minimal steady-state design-comparison setting. Its purpose is not to make clinical claims, but to define a reproducibility contract for haemodynamic simulation outputs on synthetic vascular geometry under fixed boundary conditions and a fixed solver configuration. The governing rule is straightforward: the same inputs, the same boundary conditions, and the same solver configuration must yield the same outputs. To make this enforceable, the record treats geometry, boundary conditions, solver identity and version, mesh configuration, numerical scheme, outputs, and run log as explicit artefacts within a ledger-based audit structure. This makes it possible to distinguish legitimate geometry-driven differences from untracked procedural changes. Route A is intentionally narrow in scope. It is a 2D steady incompressible flow setting on synthetic vascular geometry, designed as a controlled audit object rather than as a clinical decision system. The protocol fixes the non-geometry components of the computational pipeline and permits comparison only under declared and traceable conditions. Its contribution is therefore structural: it defines what must be locked, what may vary, and how changes are classified as PASS, FAIL, or INCOMPLETE. This record builds on the MedAI trust-graph and governance framework established in the earlier GQMI record (Zenodo DOI: 10.5281/zenodo.18757326), but is published as a separate record because its title, scope, and audit object are distinct. The present paper is the Route A haemodynamic reproducibility contract: a constrained implementation layer for synthetic steady-state CFD, rather than a general governance-only statement. This work does not provide clinical advice, patient-specific guidance, treatment recommendations, or claims of clinical efficacy. It does not claim diagnostic validity or outcome prediction. Its role is to define an auditable and reproducible computational discipline that may support later extensions, including higher-dimensional steady configurations and pulsatile regimes under stricter dynamic consistency requirements. The broader motivation is to reduce persuasive but weakly traceable interpretation of haemodynamic outputs. Rather than allowing simulation figures to function as unsupported narrative objects, this protocol requires explicit provenance, locked assumptions, and artefact-level accountability. In that sense, the record is intended as a governance-compatible reproducibility layer for haemodynamic CFD in medically adjacent settings. Axis: Peace / Non-violence / Dignity.Dual-use boundary: NO military, NO surveillance, NO coercion.