fsi2 harness: RTX_FSI2O_PATCH_STRETCH knob (the patch's across stretch, 4.0 in every recorded run; printed in both headers) — P5-3's wall-normal resolution test at fixed h: the rows ladder does not build (the overlap needs outer patch cells ≈ h/2 or larger), the stretch refines the wall cell 0.227h → 0.144h → 0.088h at 4/8/16 while the outer cells grow

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_march.rs

@@ -100,7 +100,7 @@ pub fn run_march_overset(case: BenchmarkCase, config: &OversetMarchConfig) -> Ov
     // 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, patch convection {:?}, bg convection {:?}",
+        "  coupling: {} (reuse {}, ω0 {}, c1 {}), floor {:.1e}, rtol {:.1e}, stall accept {:.1e}, max subit {}, predictor {}, s = {}, patch offset {} h × {} rows, patch convection {:?}, bg convection {:?}, patch stretch {}",
         cfg.coupler,
         cfg.reuse,
         cfg.initial_relaxation,
@@ -115,6 +115,7 @@ pub fn run_march_overset(case: BenchmarkCase, config: &OversetMarchConfig) -> Ov
         std::env::var("RTX_FSI2O_PATCH_ROWS").unwrap_or_else(|_| "12".into()),
         super::overset::patch_convection(),
         super::overset::bg_convection(),
+        super::overset::patch_stretch(),
     );
 
     // Phase 1: rigid flag to t_release (`RTX_FSI2O_LOAD=dir` replaces the