fix: generic mass extraction in solve_simulation.py (beam + bracket)

- Extract mass RIGHT AFTER geometry rebuild while part is work part
- Replace unreliable p173 expression lookup with MeasureManager
- Skip re-extraction if mass already captured during rebuild
- Relax displacement constraint to 20mm (DEC-HB-012, CEO approved)

Root cause: journal hardcoded M1_Blank for bracket, failed silently on Beam.prt
Fix by: NX Expert + Manager diagnosis

optimization_engine/nx/solve_simulation.py

@@ -1013,6 +1013,15 @@ def solve_simple_workflow(
                 theSession.DeleteUndoMark(markId_update, "NX update")
                 print(f"[JOURNAL]   Geometry rebuilt ({nErrs} errors)")
 
+                # Extract mass NOW while geometry part is work part and freshly rebuilt
+                # This is the most reliable timing — solid bodies reflect updated parameters
+                print(f"[JOURNAL]   Extracting mass from {workPart.Name}...")
+                try:
+                    mass_kg = extract_part_mass(theSession, workPart, working_dir)
+                    print(f"[JOURNAL]   Mass extracted: {mass_kg:.6f} kg")
+                except Exception as mass_err:
+                    print(f"[JOURNAL]   WARNING: Mass extraction after rebuild failed: {mass_err}")
+
                 # Save geometry part
                 print(f"[JOURNAL]   Saving geometry part...")
                 partSaveStatus_geom = workPart.Save(
@@ -1171,25 +1180,22 @@ def solve_simple_workflow(
     )
 
     # Extract mass and write to _temp_mass.txt
-    # Strategy: try expression lookup first, fall back to MeasureManager
+    # Strategy: Use MeasureManager on geometry part (most reliable)
+    # Note: Mass may have already been extracted during geometry rebuild phase above.
+    # This post-solve extraction ensures we have mass even if no expression updates were done.
     try:
         mass_value = None
 
-        # Attempt 1: Read mass from expression p173 on geometry part
-        try:
-            for part in theSession.Parts:
-                part_type = type(part).__name__
-                if "fem" not in part_type.lower() and "sim" not in part_type.lower():
-                    for expr in part.Expressions:
-                        if expr.Name == "p173":
-                            mass_value = expr.Value
-                            print(f"[JOURNAL] Mass expression p173 = {mass_value}")
-                            break
-                    break
-        except Exception as expr_err:
-            print(f"[JOURNAL] Expression lookup failed: {expr_err}")
+        # Check if mass was already written during geometry rebuild
+        mass_file = os.path.join(working_dir, "_temp_mass.txt")
+        if os.path.exists(mass_file) and expression_updates:
+            print(f"[JOURNAL] Mass already extracted during geometry rebuild phase")
+            with open(mass_file, "r") as f:
+                content = f.read().strip()
+                print(f"[JOURNAL]   Existing mass file: {content}")
+            mass_value = -1  # sentinel to skip re-extraction
 
-        # Attempt 2: Use MeasureManager (more reliable for derived/measurement expressions)
+        # Use MeasureManager if mass not yet extracted
         if mass_value is None:
             print(f"[JOURNAL] Expression p173 not found, using MeasureManager fallback...")
             geom_part = None
@@ -1206,12 +1212,12 @@ def solve_simple_workflow(
                     print(f"[JOURNAL] MeasureManager failed: {mm_err}")
 
         # Write mass file (extract_part_mass may have already written it, but ensure consistency)
-        if mass_value is not None:
+        if mass_value is not None and mass_value != -1:
             mass_file = os.path.join(working_dir, "_temp_mass.txt")
             with open(mass_file, "w") as f:
                 f.write(f"p173={mass_value}\n")
             print(f"[JOURNAL] Wrote mass to {mass_file}")
-        else:
+        elif mass_value is None:
             print(f"[JOURNAL] WARNING: Could not extract mass via expression or MeasureManager")
     except Exception as e:
         print(f"[JOURNAL] WARNING: Mass extraction failed: {e}")