diff --git a/crates/specialized/rtx-cfd/tests/embedded_fresh_cell_falsifier.rs b/crates/specialized/rtx-cfd/tests/embedded_fresh_cell_falsifier.rs
index db950af..f5c82d3 100644
--- a/crates/specialized/rtx-cfd/tests/embedded_fresh_cell_falsifier.rs
+++ b/crates/specialized/rtx-cfd/tests/embedded_fresh_cell_falsifier.rs
@@ -141,6 +141,7 @@ async fn run(moving: bool, dt: f64, t_end: f64) -> CfdResult<Vec<Record>> {
             tolerance: 1e-8,
             poisson_solver: PoissonSolverKind::Multigrid,
             poisson_precision: rtx_cfd::solvers::incompressible::MgPrecision::F64,
+            poisson_smoother: rtx_cfd::solvers::incompressible::MgSmoother::Lexicographic,
             ..EmbeddedParameters::default()
         },
     )?;
diff --git a/crates/specialized/rtx-cfd/tests/embedded_moving.rs b/crates/specialized/rtx-cfd/tests/embedded_moving.rs
index 77f54e6..2059aad 100644
--- a/crates/specialized/rtx-cfd/tests/embedded_moving.rs
+++ b/crates/specialized/rtx-cfd/tests/embedded_moving.rs
@@ -81,6 +81,7 @@ fn solver(n: usize) -> CfdResult<EmbeddedPisoSolver> {
             tolerance: 1e-8,
             poisson_solver: PoissonSolverKind::Multigrid,
             poisson_precision: rtx_cfd::solvers::incompressible::MgPrecision::F64,
+            poisson_smoother: rtx_cfd::solvers::incompressible::MgSmoother::Lexicographic,
             ..EmbeddedParameters::default()
         },
     )?;
diff --git a/crates/specialized/rtx-cfd/tests/overset_cfd23.rs b/crates/specialized/rtx-cfd/tests/overset_cfd23.rs
index 5ee627b..e73eab9 100644
--- a/crates/specialized/rtx-cfd/tests/overset_cfd23.rs
+++ b/crates/specialized/rtx-cfd/tests/overset_cfd23.rs
@@ -154,6 +154,7 @@ impl Composite {
                 },
                 poisson_solver: PoissonSolverKind::Multigrid,
                 poisson_precision: MgPrecision::F64,
+                poisson_smoother: rtx_cfd::solvers::incompressible::MgSmoother::Lexicographic,
                 // The harness's finding: upwind's numerical viscosity
                 // suppressed CFD3's shedding entirely.
                 convection_scheme: ConvectionScheme::TvdVanAlbada,
diff --git a/crates/specialized/rtx-cfd/tests/poisson_equivalence.rs b/crates/specialized/rtx-cfd/tests/poisson_equivalence.rs
index 7bf84f3..b26eb34 100644
--- a/crates/specialized/rtx-cfd/tests/poisson_equivalence.rs
+++ b/crates/specialized/rtx-cfd/tests/poisson_equivalence.rs
@@ -439,6 +439,7 @@ async fn embedded_mms_with(
             tolerance: 1e-8,
             poisson_solver: kind,
             poisson_precision: precision,
+            poisson_smoother: rtx_cfd::solvers::incompressible::MgSmoother::Lexicographic,
             ..EmbeddedParameters::default()
         },
     )?;
@@ -600,6 +601,7 @@ async fn without_a_body_the_embedded_solver_is_piso_to_the_bit_with_multigrid()
             tolerance: 1e-8,
             poisson_solver: PoissonSolverKind::Multigrid,
             poisson_precision: rtx_cfd::solvers::incompressible::MgPrecision::F64,
+            poisson_smoother: rtx_cfd::solvers::incompressible::MgSmoother::Lexicographic,
             ..EmbeddedParameters::default()
         },
     )?;
@@ -665,6 +667,7 @@ async fn channel_with_circle(kind: PoissonSolverKind) -> CfdResult<(FlowField, u
             },
             poisson_solver: kind,
             poisson_precision: rtx_cfd::solvers::incompressible::MgPrecision::F64,
+            poisson_smoother: rtx_cfd::solvers::incompressible::MgSmoother::Lexicographic,
             ..EmbeddedParameters::default()
         },
     )?;
diff --git a/crates/specialized/rtx-cfd/tests/turek_hron_cfd.rs b/crates/specialized/rtx-cfd/tests/turek_hron_cfd.rs
index dbe23b8..82fc6bf 100644
--- a/crates/specialized/rtx-cfd/tests/turek_hron_cfd.rs
+++ b/crates/specialized/rtx-cfd/tests/turek_hron_cfd.rs
@@ -120,6 +120,7 @@ async fn run_cfd1(ny: usize) -> CfdResult<Cfd1> {
         },
         poisson_solver: PoissonSolverKind::Multigrid,
         poisson_precision: rtx_cfd::solvers::incompressible::MgPrecision::F64,
+        poisson_smoother: rtx_cfd::solvers::incompressible::MgSmoother::Lexicographic,
         ..EmbeddedParameters::default()
     };
     let mut solver = EmbeddedPisoSolver::new(config, params)?;
diff --git a/crates/specialized/rtx-cfd/tests/turek_hron_cfd23.rs b/crates/specialized/rtx-cfd/tests/turek_hron_cfd23.rs
index 49a2fd7..24e2e02 100644
--- a/crates/specialized/rtx-cfd/tests/turek_hron_cfd23.rs
+++ b/crates/specialized/rtx-cfd/tests/turek_hron_cfd23.rs
@@ -127,6 +127,7 @@ impl Runner {
             },
             poisson_solver: PoissonSolverKind::Multigrid,
             poisson_precision: rtx_cfd::solvers::incompressible::MgPrecision::F64,
+            poisson_smoother: rtx_cfd::solvers::incompressible::MgSmoother::Lexicographic,
             // Upwind's numerical viscosity (|u| h / 2 ~ 10x the physical nu
             // on these grids) suppressed CFD3's vortex shedding entirely:
             // the ny = 41 upwind run produced ONE lift zero-crossing in
diff --git a/crates/specialized/rtx-fsi/tests/turek_hron_fsi1.rs b/crates/specialized/rtx-fsi/tests/turek_hron_fsi1.rs
index ece495f..5d6eed7 100644
--- a/crates/specialized/rtx-fsi/tests/turek_hron_fsi1.rs
+++ b/crates/specialized/rtx-fsi/tests/turek_hron_fsi1.rs
@@ -324,6 +324,7 @@ fn fsi1_coupled_cylinder_and_flag() {
         },
         poisson_solver: PoissonSolverKind::Multigrid,
         poisson_precision: rtx_cfd::solvers::incompressible::MgPrecision::F64,
+        poisson_smoother: rtx_cfd::solvers::incompressible::MgSmoother::Lexicographic,
         // Upwind, deliberately: FSI1 is a steady FIXED-POINT problem, and
         // the TVD limiter's switching keeps the steady load chattering by
         // ~0.5% (a known property of limited schemes — they stall short of