Snapshot WIP: solver HP epic progress, BPHX/HX physics, BMAD skill refresh.

Capture uncommitted solver robustness work (regularization, domain errors, linear solver lifecycle, tube DP/MSH), web workbench updates, and synced BMAD skills across IDE agent folders before starting BPHX pressure-drop.

Co-authored-by: Cursor <cursoragent@cursor.com>

crates/solver/tests/flooded_4port_dof.rs

@@ -169,7 +169,9 @@ fn build_flooded_watercooled() -> System {
         .add_edge_with_ports(n_evap, 3, n_ewo, 0)
         .expect("chw out");
 
-    system.finalize().expect("finalize flooded water-cooled graph");
+    system
+        .finalize()
+        .expect("finalize flooded water-cooled graph");
     system
 }
 
@@ -179,12 +181,14 @@ fn flooded_watercooled_4port_is_dof_balanced() {
     let report = system.dof_report();
 
     assert_eq!(
-        report.n_unknowns, 19,
+        report.n_unknowns,
+        19,
         "unknowns: 3 branches + 2×8 edges = 19\n{}",
         report.summary()
     );
     assert_eq!(
-        report.n_equations, 19,
+        report.n_equations,
+        19,
         "equations must match unknowns\n{}",
         report.summary()
     );
@@ -206,7 +210,12 @@ fn flooded_watercooled_4port_is_dof_balanced() {
         .iter()
         .find(|c| c.component_name == "evap")
         .expect("evap in ledger");
-    assert_eq!(evap.n_equations, 4, "ΔP + energy + sat-vapor + secondary energy");
+    // Secondary isobaric P closure was added for the Modelica MassFlowSource_T
+    // (Free P) pattern: the HX propagates the sink pressure to the source edge.
+    assert_eq!(
+        evap.n_equations, 5,
+        "ΔP + energy + sat-vapor + secondary P + secondary energy"
+    );
     assert!(
         evap.roles.iter().any(|r| matches!(
             r,
@@ -250,7 +259,8 @@ fn quality_control_without_extra_free_still_same_equation_count() {
         without_q.n_equations(),
         "quality_control must replace sat-vapor closure, not add a residual"
     );
-    assert_eq!(with_q.n_equations(), 4);
+    // 3 refrigerant rows (ΔP + energy + closure) + 2 secondary (P + energy, same branch).
+    assert_eq!(with_q.n_equations(), 5);
 }
 
 #[test]