test(rtx-fsi): RTX_FSI{2,3}_UMEAN inflow override for the TWIN-1 parameter sweep

case_from_env applies the knob over the case's benchmark inflow; unset,
the same f64 flows and both committed defaults are verified
digit-identical in vivo (physics lines diff-clean vs same-day
baselines; only wall-split timing percentages moved). Physics bands in
both tests are guarded to benchmark inflow — an off-benchmark march
(the sweep) asserts machinery invariants only; its bands live in the
TWIN-1 composition harness (omni-cortex
docs/twin_composition_campaign.md). The override prints loudly so
sweep logs are self-describing.

Co-Authored-By: Claude Fable 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01X2GmJXeQ2njUecEKiJZ1G2

crates/specialized/rtx-fsi/tests/turek_hron_fsi3.rs

@@ -152,7 +152,8 @@ fn fsi3_added_mass_flag() {
     let MarchConfig {
         ny, flag_nx, t_end, ..
     } = config;
-    let result = run_march(FSI3, &config);
+    let case = fsi2_harness::case_from_env("FSI3", FSI3);
+    let result = run_march(case, &config);
     let w = result.window(2.0);
 
     println!(
@@ -221,13 +222,19 @@ fn fsi3_added_mass_flag() {
     // horizons pin the MEASURED settled cycle, band-generous across
     // the two grids that measured it. If a change moves any of these
     // numbers, that is a finding either way and must be loud.)
-    let default_release = config.subcycle == 2
+    // Bands were measured at the BENCHMARK inflow; an overridden u_mean
+    // (`RTX_FSI3_UMEAN`) pins nothing here. Machinery invariants above
+    // stay asserted at every inflow.
+    let benchmark_inflow = case.u_mean.to_bits() == FSI3.u_mean.to_bits();
+    let default_release = benchmark_inflow
+        && config.subcycle == 2
         && config.mask_hysteresis == 0.0
         && config.coupler == "iqn"
         && ny == 62
         && flag_nx == 35
         && (t_end - 4.2).abs() < 1e-9;
-    let hyst_cycle = config.subcycle == 2
+    let hyst_cycle = benchmark_inflow
+        && config.subcycle == 2
         && config.mask_hysteresis > 0.0
         && config.coupler == "iqn"
         && flag_nx == 35