FSI2 overset march: print every coupling setting once (coupler, floor, rtol, stall accept, max subit, predictor, s, patch offset × rows) and add RTX_FSI2O_LOAD_SETTLE (rigid steps after a loaded state, clock put back; default 20) — P5-3 lost a day to the default floor 2e-4 against the overnight marches' 1e-6: at 2e-4 every s = 1 release at ny = 62 rings at ± 1000 N/m (the flag's thickness breathing), at 1e-6 all are clean, thick patches included

Co-Authored-By: Claude Fable 5.1 <[email protected]>
Claude-Session: https://claude.ai/code/session_0116sg1Qz1gMv9hdcKP1XUam

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

@@ -97,6 +97,23 @@ pub fn run_march_overset(case: BenchmarkCase, config: &OversetMarchConfig) -> Ov
     let dt_fluid = fluid.dt_fluid;
     let dt = dt_fluid * cfg.subcycle as f64;
     let zero_d = vec![0.0; 2 * fluid.interface.wetted.len()];
+    // Every setting the acceptance rule reads, printed once: P5-3 lost a
+    // day to a floor of 2e-4 against the overnight marches' 1e-6.
+    println!(
+        "  coupling: {} (reuse {}, ω0 {}, c1 {}), floor {:.1e}, rtol {:.1e}, stall accept {:.1e}, max subit {}, predictor {}, s = {}, patch offset {} h × {} rows",
+        cfg.coupler,
+        cfg.reuse,
+        cfg.initial_relaxation,
+        cfg.c1_interface,
+        cfg.tol_floor,
+        cfg.rtol,
+        cfg.stall_accept,
+        cfg.max_subiterations,
+        cfg.predictor,
+        cfg.subcycle,
+        std::env::var("RTX_FSI2O_PATCH_OFFSET").unwrap_or_else(|_| "6".into()),
+        std::env::var("RTX_FSI2O_PATCH_ROWS").unwrap_or_else(|_| "12".into()),
+    );
 
     // Phase 1: rigid flag to t_release (`RTX_FSI2O_LOAD=dir` replaces the
     // march with the saved state; `RTX_FSI2O_SAVE=dir` saves it).
@@ -109,6 +126,28 @@ pub fn run_march_overset(case: BenchmarkCase, config: &OversetMarchConfig) -> Ov
             "the saved state is at t = {t}, not t_release = {}",
             cfg.t_release
         );
+        // The saved state is the FIELDS; the solvers' own warm state (the
+        // Schwarz acceptor warm start, the fringe flux correction, the
+        // embedded body's old volume fractions) is not in it, and a
+        // release straight off the load carries a pressure-level
+        // transient that the live march does not (P5-3: drag 27 vs 132
+        // twenty steps in, lift ± 1000 vs ± 4 — enough to kick the flag's
+        // thickness breathing at ny = 62). `RTX_FSI2O_LOAD_SETTLE=N`
+        // (default 20) rigid steps rebuild that state on the steady rigid
+        // flow; the clock is put back so the runs stay comparable.
+        let settle: usize = std::env::var("RTX_FSI2O_LOAD_SETTLE")
+            .ok()
+            .and_then(|v| v.parse().ok())
+            .unwrap_or(20);
+        let (d0, l0) = fluid.measure_force();
+        for _ in 0..settle {
+            fluid.step().expect("settle fluid step");
+        }
+        fluid.solver.set_time(t);
+        let (d1, l1) = fluid.measure_force();
+        println!(
+            "  settled the loaded state with {settle} rigid steps: wall drag {d0:.2} → {d1:.2}, lift {l0:.2} → {l1:.2}; clock back to t = {t:.4}"
+        );
     } else {
         for _ in 0..rigid_steps {
             fluid.step().expect("rigid fluid step");