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/serialization_test.rs

@@ -65,8 +65,10 @@ fn build_single_compressor_system() -> System {
     system
 }
 
-/// Helper: create a system with two components and an edge between them,
-/// plus a thermal coupling.
+/// Helper: create a system with two components in a 2-edge cycle,
+/// plus a thermal coupling. CM1.4: a single edge between two 3-eq
+/// compressors is over-constrained; the second edge makes the topology
+/// under-constrained so serialization round-trips can finalize.
 fn build_two_component_system() -> System {
     let mut system = System::new();
 
@@ -137,8 +139,13 @@ fn build_two_component_system() -> System {
     let node_comp2 = system.add_component(Box::new(comp2));
     system.register_component_name("condenser", node_comp2);
 
-    // Add edge between them
-    system.add_edge(node_comp, node_comp2).expect("add edge");
+    // Add two edges forming a cycle so the topology is not over-constrained.
+    system
+        .add_edge(node_comp, node_comp2)
+        .expect("add edge comp->cond");
+    system
+        .add_edge(node_comp2, node_comp)
+        .expect("add edge cond->comp");
 
     // Add thermal coupling
     let coupling = ThermalCoupling::new(