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>

examples/test_journal_optimization.py

@@ -27,13 +27,23 @@ from optimization_engine.result_extractors.extractors import (
 )
 
 
+# Global variable to store current design variables for the simulation runner
+_current_design_vars = {}
+
+
 def bracket_model_updater(design_vars: dict):
-    """Update bracket model parameters."""
-    prt_file = project_root / "examples/bracket/Bracket.prt"
-    print(f"\n[MODEL UPDATE] {prt_file.name}")
+    """
+    Store design variables for the simulation runner.
+
+    Note: We no longer directly update the .prt file here.
+    Instead, design variables are passed to the journal which applies them in NX.
+    """
+    global _current_design_vars
+    _current_design_vars = design_vars.copy()
+
+    print(f"\n[MODEL UPDATE] Design variables prepared")
     for name, value in design_vars.items():
         print(f"  {name} = {value:.4f}")
-    update_nx_model(prt_file, design_vars, backup=False)
 
 
 def bracket_simulation_runner() -> Path:
@@ -42,23 +52,29 @@ def bracket_simulation_runner() -> Path:
 
     This connects to the running Simcenter3D GUI and:
     1. Opens the .sim file
-    2. Updates the FEM component
-    3. Solves the simulation
-    4. Returns path to .op2 file
+    2. Applies expression updates in the journal
+    3. Updates geometry and FEM
+    4. Solves the simulation
+    5. Returns path to .op2 file
     """
+    global _current_design_vars
     sim_file = project_root / "examples/bracket/Bracket_sim1.sim"
 
     print("\n[SIMULATION] Running via journal on NX GUI...")
     print(f"  SIM file: {sim_file.name}")
+    if _current_design_vars:
+        print(f"  Expression updates: {_current_design_vars}")
 
     try:
         # Run solver via journal (connects to running NX GUI)
+        # Pass expression updates directly to the journal
         op2_file = run_nx_simulation(
             sim_file=sim_file,
             nastran_version="2412",
             timeout=300,  # 5 minute timeout
             cleanup=True,  # Clean up temp files
-            use_journal=True  # Use journal mode (requires NX GUI open)
+            use_journal=True,  # Use journal mode (requires NX GUI open)
+            expression_updates=_current_design_vars  # Pass design vars to journal
         )
 
         print(f"[SIMULATION] Complete! Results: {op2_file.name}")