fsi2 harness: RTX_FSI2O_PATCH_CONVECTION knob (tvd default / upwind / none) on the overset patch, printed in the march's coupling header and the replay's PRESCRIBED header — P5-3's near-wake dispersion test on the ny 62 fixed-motion replay; harness files under the pinned toolchain's cargo fmt

Co-Authored-By: Claude Fable 5.1 <[email protected]>
Claude-Session: https://claude.ai/code/session_01LzcjQX7tvgn87CQCyg9Cfr

crates/specialized/rtx-fsi/tests/fsi2_harness/overset.rs

@@ -12,8 +12,8 @@ use std::cell::Cell;
 use std::sync::{Arc, RwLock};
 
 use nalgebra::Vector3;
-use rtx_cfd::mesh::patch_gen::cylinder_flag_patch_deformed;
 use rtx_cfd::mesh::PatchSide;
+use rtx_cfd::mesh::patch_gen::cylinder_flag_patch_deformed;
 use rtx_cfd::solvers::incompressible::{
     AleBoundaries, ConvectionScheme, CurvilinearParameters, CurvilinearPisoSolver,
     EmbeddedParameters, EmbeddedPisoSolver, FlowField, MgPrecision, NormalDiffusion, OversetField,
@@ -24,7 +24,7 @@ use rtx_cfd::{CfdConfig, CfdResult};
 use rtx_fea::mesh::{Mesh, NodeId};
 use rtx_fsi::{FluidFace, WettedSurface};
 
-use super::{flag_mesh, inflow_for, BenchmarkCase, Interface, FLAG_X1, H, L, NU_F, RHO_F};
+use super::{BenchmarkCase, FLAG_X1, H, Interface, L, NU_F, RHO_F, flag_mesh, inflow_for};
 
 const CYL_CENTRE: [f64; 2] = [0.2, 0.2];
 const CYL_R: f64 = 0.05;
@@ -45,6 +45,17 @@ fn patch_offset_h() -> f64 {
         .unwrap_or(6.0)
 }
 
+/// The patch's convection scheme (`RTX_FSI2O_PATCH_CONVECTION`: `tvd`
+/// (default, van Albada), `upwind`, `none`) — P5-3's near-wake dispersion
+/// knob on the fixed-motion replay.
+pub fn patch_convection() -> PatchConvection {
+    match std::env::var("RTX_FSI2O_PATCH_CONVECTION").as_deref() {
+        Ok("upwind") => PatchConvection::Upwind,
+        Ok("none") => PatchConvection::None,
+        _ => PatchConvection::TvdVanAlbada,
+    }
+}
+
 /// The patch's across-rows (`RTX_FSI2O_PATCH_ROWS`, 12; scale it with the
 /// offset to keep the wall spacing).
 fn patch_rows() -> usize {
@@ -327,7 +338,7 @@ impl OversetFluid {
             config,
             CurvilinearParameters {
                 tolerance: 1e-5,
-                convection: PatchConvection::TvdVanAlbada,
+                convection: patch_convection(),
                 normal_diffusion: NormalDiffusion::LineImplicit,
                 ..CurvilinearParameters::default()
             },