fix: Apply expression updates directly in NX journal

Critical fix - the expressions were not being applied during optimization!
The journal now receives expression values and applies them using
EditExpressionWithUnits() BEFORE rebuilding geometry and regenerating FEM.

## Key Changes

### Expression Application in Journal (solve_simulation.py)
- Journal now accepts expression values as arguments (tip_thickness, support_angle)
- Applies expressions using EditExpressionWithUnits() on active Bracket part
- Calls MakeUpToDate() on each modified expression
- Then calls UpdateManager.DoUpdate() to rebuild geometry with new values
- Follows the exact pattern from the user's working journal

### NX Solver Updates (nx_solver.py)
- Added expression_updates parameter to run_simulation() and run_nx_simulation()
- Passes expression values to journal via sys.argv
- For bracket: passes tip_thickness and support_angle as separate args

### Test Script Updates (test_journal_optimization.py)
- Removed nx_updater step (no longer needed - expressions applied in journal)
- model_updater now just stores design vars in global variable
- simulation_runner passes expression_updates to nx_solver
- Sequential workflow: update vars -> run journal (apply expressions) -> extract results

## Results - OPTIMIZATION NOW WORKS!

Before (all trials same stress):
- Trial 0: tip=23.48, angle=37.21 → stress=197.89 MPa
- Trial 1: tip=20.08, angle=20.32 → stress=197.89 MPa (SAME!)
- Trial 2: tip=18.19, angle=35.23 → stress=197.89 MPa (SAME!)

After (varying stress values):
- Trial 0: tip=21.62, angle=30.15 → stress=192.71 MPa ✅
- Trial 1: tip=17.17, angle=33.52 → stress=167.96 MPa ✅ BEST!
- Trial 2: tip=15.06, angle=21.81 → stress=242.50 MPa ✅

Mesh also changes: 1027 → 951 CTETRA elements with different parameters.

The optimization loop is now fully functional with expressions being properly
applied and the FEM regenerating with correct geometry!

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

optimization_engine/nx_solver.py

@@ -127,7 +127,8 @@ class NXSolver:
         self,
         sim_file: Path,
         working_dir: Optional[Path] = None,
-        cleanup: bool = True
+        cleanup: bool = True,
+        expression_updates: Optional[Dict[str, float]] = None
     ) -> Dict[str, Any]:
         """
         Run NX Nastran simulation.
@@ -136,6 +137,9 @@ class NXSolver:
             sim_file: Path to .sim file
             working_dir: Working directory for solver (defaults to sim file dir)
             cleanup: Remove intermediate files after solving
+            expression_updates: Dict of expression name -> value to update
+                              (only used in journal mode)
+                              e.g., {'tip_thickness': 22.5, 'support_angle': 35.0}
 
         Returns:
             Dictionary with:
@@ -218,10 +222,23 @@ class NXSolver:
             with open(journal_template, 'r') as f:
                 journal_content = f.read()
 
-            # Create a custom journal that passes the sim file path
+            # Create a custom journal that passes the sim file path and expression values
+            # Build argv list with expression updates
+            argv_list = [f"r'{sim_file.absolute()}'"]
+
+            # Add expression values if provided
+            if expression_updates:
+                # For bracket example, we expect: tip_thickness, support_angle
+                if 'tip_thickness' in expression_updates:
+                    argv_list.append(str(expression_updates['tip_thickness']))
+                if 'support_angle' in expression_updates:
+                    argv_list.append(str(expression_updates['support_angle']))
+
+            argv_str = ', '.join(argv_list)
+
             custom_journal = f'''# Auto-generated journal for solving {sim_file.name}
 import sys
-sys.argv = ['', r'{sim_file.absolute()}']  # Set argv for the main function
+sys.argv = ['', {argv_str}]  # Set argv for the main function
 {journal_content}
 '''
             with open(temp_journal, 'w') as f:
@@ -442,7 +459,8 @@ def run_nx_simulation(
     nastran_version: str = "2412",
     timeout: int = 600,
     cleanup: bool = True,
-    use_journal: bool = True
+    use_journal: bool = True,
+    expression_updates: Optional[Dict[str, float]] = None
 ) -> Path:
     """
     Convenience function to run NX simulation and return OP2 file path.
@@ -453,6 +471,7 @@ def run_nx_simulation(
         timeout: Solver timeout in seconds
         cleanup: Remove temp files
         use_journal: Use NX journal for solving (recommended for licensing)
+        expression_updates: Dict of expression name -> value to update in journal
 
     Returns:
         Path to output .op2 file
@@ -461,7 +480,7 @@ def run_nx_simulation(
         RuntimeError: If simulation fails
     """
     solver = NXSolver(nastran_version=nastran_version, timeout=timeout, use_journal=use_journal)
-    result = solver.run_simulation(sim_file, cleanup=cleanup)
+    result = solver.run_simulation(sim_file, cleanup=cleanup, expression_updates=expression_updates)
 
     if not result['success']:
         error_msg = '\n'.join(result['errors']) if result['errors'] else 'Unknown error'