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+# Arsenal Development Plan — Atomizer Multi-Solver Integration
+
+> **Status:** DRAFT — pending CEO approval  
+> **Date:** 2026-06-25  
+> **Authors:** Technical Lead (architecture + feasibility), Auditor (risk + gates), Manager (orchestration)  
+> **Source docs:** Arsenal V3 Final, Tool-Agnostic Architecture, Multi-Solver Roadmap, Arsenal Reference  
+
+---
+
+## 1. Executive Summary
+
+**Goal:** Integrate the 80/20 highest-leverage open-source tools from the Atomizer Arsenal into V2, enabling fully scripted optimization without NX GUI dependency.
+
+**What this unlocks:**
+- Linux-headless optimization loops (no NX license bottleneck)
+- 100s–1000s of trials per campaign (vs. current NX-constrained budgets)
+- Multi-solver validation (CalculiX vs Nastran cross-checking)
+- Path to CFD and multi-physics (expansion sprints)
+
+**The 80/20 stack (6 sprints):**
+
+| Priority | Tool | Category | Why |
+|----------|------|----------|-----|
+| 🔴 P1 | CalculiX | FEA solver | Free structural solver, covers 80% of use cases |
+| 🔴 P1 | Gmsh | Meshing | Universal mesher, Python API, STEP import |
+| 🔴 P1 | Build123d | CAD | Code-native geometry, LLM-perfect, headless |
+| 🔴 P1 | meshio + pyNastran | Converters | Format glue between all tools |
+| 🔴 P1 | PyVista + ParaView | Post-processing | Automated visualization pipeline |
+| 🟡 P2 | pymoo | Optimization | Multi-objective (NSGA-II/III) |
+| 🟡 P2 | OpenFOAM | CFD | Thermal/flow screening |
+| 🟢 P3 | preCICE | Coupling | Thermo-structural coupling |
+| 🟢 P3 | OpenMDAO | MDO | System-level optimization |
+
+**Antoine's time commitment:** ~2–3 hours per sprint for validation gates.  
+**HQ autonomous work:** days of implementation per sprint.
+
+---
+
+## 2. Architecture Overview
+
+The Arsenal integrates through Atomizer's 3-layer tool-agnostic architecture:
+
+```
+┌─────────────────────────────────────────────────────────┐
+│  Layer 3: OPTIMIZATION INTELLIGENCE                      │
+│  AtomizerSpec v3.0 │ Optuna/pymoo │ LAC │ LLM Agents    │
+│  ── never touches tool-specific formats ──               │
+├─────────────────────────────────────────────────────────┤
+│  Layer 2: TOOL PROCESSORS (deterministic Python)         │
+│  Geometry:  nx_geometry │ build123d_geometry │ step_import│
+│  Meshing:   gmsh_mesher │ nx_mesher                      │
+│  Solvers:   nastran_solver │ calculix_solver │ openfoam   │
+│  Convert:   meshio_converter │ pynastran_bridge          │
+│  Post:      pyvista_post │ paraview_post                 │
+├─────────────────────────────────────────────────────────┤
+│  Layer 1: UNIVERSAL DATA CONTRACTS                       │
+│  AtomizerGeometry │ AtomizerMesh │ AtomizerBCs           │
+│  AtomizerMaterial │ AtomizerResults                      │
+│  ── solver-agnostic dataclasses (the Rosetta Stone) ──  │
+└─────────────────────────────────────────────────────────┘
+```
+
+**Key rule:** Adding a new tool = writing ONE processor file. Contracts never change per tool.
+
+### 2.1 V2 Repository Target Layout
+
+```
+atomizer/
+├── contracts/
+│   ├── geometry.py              # AtomizerGeometry
+│   ├── mesh.py                  # AtomizerMesh
+│   ├── boundary_conditions.py   # AtomizerBCs
+│   ├── material.py              # AtomizerMaterial
+│   ├── results.py               # AtomizerResults
+│   └── validators.py            # Cross-contract sanity checks
+├── processors/
+│   ├── base.py                  # Abstract base classes
+│   ├── geometry/
+│   │   ├── build123d_geometry.py
+│   │   ├── nx_geometry.py
+│   │   └── step_import.py
+│   ├── meshing/
+│   │   ├── gmsh_mesher.py
+│   │   └── nx_mesher.py
+│   ├── solvers/
+│   │   ├── nastran_solver.py
+│   │   ├── calculix_solver.py
+│   │   └── openfoam_solver.py   # Sprint 4
+│   ├── converters/
+│   │   ├── meshio_converter.py
+│   │   └── pynastran_bridge.py
+│   └── postprocessing/
+│       ├── pyvista_post.py
+│       └── paraview_post.py
+├── orchestrator/
+│   ├── pipeline.py              # Solver-agnostic run sequencing
+│   ├── auto_select.py           # Toolchain routing logic
+│   └── coupling.py              # Sprint 5: preCICE
+├── optimization/
+│   ├── engine.py                # Core optimization loop
+│   ├── optuna_backend.py
+│   └── pymoo_backend.py         # Sprint 6
+└── mcp_servers/                 # Sprint 2-3
+    ├── calculix/
+    ├── gmsh/
+    ├── build123d/
+    └── pynastran/
+```
+
+---
+
+## 3. Current Environment Assessment
+
+| Item | Status | Action Required |
+|------|--------|----------------|
+| V2 repo (`atomizer/` package) | ❌ Not yet created — still V1 flat layout | Sprint 0: scaffold package structure |
+| pyNastran | ✅ Installed | None |
+| CalculiX (ccx) | ❌ Not installed | `apt install calculix-ccx` or Docker |
+| Gmsh | ❌ Not installed | `pip install gmsh pygmsh` |
+| Build123d | ❌ Not installed | `pip install build123d` |
+| meshio | ❌ Not installed | `pip install meshio` |
+| PyVista | ❌ Not installed | `pip install pyvista` |
+| ParaView/pvpython | ❌ Not installed | `apt install paraview` |
+| pymoo | ❌ Not installed | `pip install pymoo` (Sprint 6) |
+| OpenFOAM | ❌ Not installed | Docker recommended (Sprint 4) |
+
+**First blocker:** Package installs on T420. Either direct install or Docker-based dev environment.
+
+---
+
+## 4. Sprint Plan
+
+### Sprint 0: Environment + Scaffold (1–2 days)
+**Goal:** Working dev environment and V2 package skeleton.
+
+| Task | Owner | Autonomy | Deliverable |
+|------|-------|----------|-------------|
+| Install core Python packages (gmsh, build123d, meshio, pyvista) | Developer/IT | 🟢 Full | Working imports |
+| Install CalculiX (`apt install calculix-ccx`) | Developer/IT | 🟢 Full | `ccx` on PATH |
+| Scaffold `atomizer/` package with `__init__.py` stubs | Developer | 🟢 Full | Package importable |
+| Create `tests/benchmarks/` with 3 analytical reference cases | Tech Lead | 🟢 Full | JSON expected-value files |
+
+**Analytical benchmarks (known-answer problems):**
+1. **Cantilever beam** — tip deflection = PL³/3EI (linear static)
+2. **Plate with hole** — SCF ≈ 3.0 at hole edge (stress concentration)
+3. **Simply supported beam** — first natural frequency = (π²/L²)√(EI/ρA) (modal)
+
+**Antoine gate:** None — this is infrastructure.
+
+---
+
+### Sprint 1: Contracts + Structural Bridge Baseline (1 week)
+**Goal:** Contract-driven NX/Nastran baseline with format conversion verification.
+
+| Task | Owner | Autonomy | Deliverable |
+|------|-------|----------|-------------|
+| Implement 5 contract dataclasses | Developer | 🟢 95% | `contracts/*.py` with full type hints |
+| Implement `validators.py` | Developer | 🟢 95% | Unit-consistent checks, BC physics checks |
+| Implement `processors/base.py` abstract classes | Tech Lead → Developer | 🟢 95% | `GeometryProcessor`, `MeshProcessor`, `SolverProcessor` ABCs |
+| Wrap existing NX/Nastran into `nastran_solver.py` | NX Expert → Developer | 🟡 70% | Existing workflow through new interface |
+| Implement `meshio_converter.py` | Developer | 🟢 95% | BDF ↔ INP ↔ MSH ↔ VTK round-trip |
+| Implement `pynastran_bridge.py` | Developer | 🟢 95% | BDF read/modify, OP2 parse → AtomizerResults |
+| Implement `pipeline.py` skeleton | Tech Lead → Developer | 🟢 90% | Sequential pipeline runner |
+| Unit tests for all contracts + converters | Developer | 🟢 95% | pytest suite passing |
+
+**Success criterion:** Existing NX/Nastran workflow passes through new architecture with zero regression.
+
+**Antoine gate:** Provide 3 trusted benchmark studies with known expected outputs for parity check.
+
+**Risk:** Hidden assumptions in legacy NX/Nastran parsing may break when abstracted.  
+**Mitigation:** Run full diff on old vs new output before declaring parity.
+
+---
+
+### Sprint 2: Open Structural Lane — CalculiX + Gmsh + Build123d (1–2 weeks)
+**Goal:** Full Linux-headless structural optimization loop with zero NX dependency.
+
+| Task | Owner | Autonomy | Deliverable |
+|------|-------|----------|-------------|
+| Implement `build123d_geometry.py` | Developer | 🟢 90% | DV dict → Build123d → STEP |
+| Implement `step_import.py` | Developer | 🟢 95% | STEP → AtomizerGeometry |
+| Implement `gmsh_mesher.py` | Developer | 🟢 90% | STEP → Gmsh → AtomizerMesh (with quality metrics) |
+| Implement `calculix_solver.py` | Tech Lead → Developer | 🟡 80% | .inp generation + ccx exec + .frd parsing → AtomizerResults |
+| Implement `pyvista_post.py` | Developer | 🟢 95% | AtomizerResults → contour plots (PNG/VTK) |
+| Implement `optuna_backend.py` (adapted) | Optimizer → Developer | 🟢 90% | Contract-aware Optuna loop |
+| Run 3 analytical benchmarks through full pipeline | Tech Lead | 🟢 90% | Pass/fail report vs known answers |
+| CalculiX vs Nastran parity comparison | Tech Lead | 🟡 70% | Delta report on shared benchmark |
+
+**Demo scenario:**
+```
+Parametric bracket (thickness, fillet_radius, rib_width)
+→ Build123d generates STEP
+→ Gmsh meshes
+→ CalculiX solves (SOL 101 equivalent)
+→ PyVista renders stress contour
+→ Optuna optimizes for min mass @ stress constraint
+→ Full loop on Linux, no NX
+```
+
+**Success criteria:**
+- [ ] 3 analytical benchmarks pass within 2% of theory
+- [ ] CalculiX vs Nastran delta < 5% on stress/displacement for shared benchmark
+- [ ] Full optimization loop completes 50+ trials unattended
+
+**Antoine gate:** 
+1. Approve CalculiX vs Nastran parity tolerance (proposed: 5% on stress, 3% on displacement)
+2. Validate one benchmark result manually
+3. Review Build123d geometry quality for representative model
+
+**Risks:**
+- Gmsh mesh quality on sharp fillets → **Mitigation:** define mesh size presets, add Jacobian quality check
+- CalculiX .frd parsing edge cases → **Mitigation:** test against multiple element types (CQUAD4 equivalent, CHEXA equivalent)
+- Build123d geometry failures on complex shapes → **Mitigation:** start with simple parametric bracket, escalate complexity gradually
+
+---
+
+### Sprint 3: MVP Hardening + Client-Grade Post-Processing (1 week)
+**Goal:** Production-quality outputs from both solver lanes, side-by-side comparison capability.
+
+| Task | Owner | Autonomy | Deliverable |
+|------|-------|----------|-------------|
+| Implement `paraview_post.py` | Developer | 🟢 90% | Publication-quality figures (headless pvpython) |
+| Implement `auto_select.py` | Tech Lead → Developer | 🟡 75% | Toolchain routing rules (NX lane vs open lane) |
+| Implement `spec/validator.py` | Developer | 🟢 95% | AtomizerSpec v3.0 schema validation |
+| Dual-lane comparison report | Post-Processor → Developer | 🟢 85% | Side-by-side Nastran vs CalculiX with pass/fail |
+| Regression test suite | Auditor → Developer | 🟢 90% | Automated benchmark + parity checks |
+| MCP-CalculiX server | MCP Engineer → Developer | 🟡 70% | Tool-call interface for CalculiX |
+| MCP-Gmsh server | MCP Engineer → Developer | 🟡 70% | Tool-call interface for Gmsh |
+| Documentation: Integration Guide | Secretary | 🟢 95% | `docs/DEV/INTEGRATION-GUIDE.md` |
+
+**Success criteria:**
+- [ ] Dual-lane comparison passes on all 3 benchmarks
+- [ ] Automated regression suite runs in CI
+- [ ] MCP servers pass basic smoke tests
+
+**Antoine gate:**
+1. Approve report template and required figure list
+2. Define auto-select routing rules (when NX vs when open-source)
+3. Sign off MVP as "usable for real studies"
+
+**🏁 MVP EXIT — after Sprint 3, Atomizer can run full structural optimization on Linux without NX.**
+
+---
+
+### Sprint 4: CFD Lane — OpenFOAM (1–2 weeks)
+**Goal:** Automated CFD/thermal screening within the same orchestration framework.
+
+| Task | Owner | Autonomy | Deliverable |
+|------|-------|----------|-------------|
+| Install OpenFOAM (Docker recommended) | IT | 🟢 Full | Working `simpleFoam` / `buoyantSimpleFoam` |
+| Implement `openfoam_solver.py` | Tech Lead → Developer | 🟡 65% | Case generation + execution + result parsing |
+| Extend `gmsh_mesher.py` with CFD presets | Developer | 🟡 75% | Boundary layer meshing, inflation layers |
+| Extend contracts for CFD quantities | Tech Lead → Developer | 🟡 70% | Pressure, velocity, temperature fields in AtomizerResults |
+| 2 CFD validation cases | Tech Lead | 🟡 60% | Lid-driven cavity + pipe flow (known analytical/reference) |
+
+**Demo scenario:**
+```
+Electronics enclosure airflow
+→ STEP → Gmsh CFD mesh → OpenFOAM (buoyantSimpleFoam)
+→ PyVista thermal map + pressure drop
+→ Variant ranking by max temperature
+```
+
+**Antoine gate:**
+1. Lock one validated starter case template before generalization
+2. Define screening-fidelity defaults (mesh size, turbulence model)
+3. Validate thermal results against engineering judgment
+
+**Risk:** OpenFOAM setup complexity is high. Dictionary validation is error-prone.  
+**Mitigation:** Start with one locked template, generalize only after it works.
+
+---
+
+### Sprint 5: Coupled Thermo-Structural — preCICE (1–2 weeks)
+**Goal:** Two-way coupled OpenFOAM ↔ CalculiX simulations.
+
+| Task | Owner | Autonomy | Deliverable |
+|------|-------|----------|-------------|
+| Install preCICE + adapters | IT | 🟢 Full | preCICE + CalculiX adapter + OpenFOAM adapter |
+| Implement `coupling.py` | Tech Lead → Developer | 🟡 60% | Coupled orchestration with convergence monitoring |
+| 1 coupled benchmark | Tech Lead | 🔴 50% | Heated plate with thermal expansion |
+
+**Antoine gate:** Approve coupling parameters and convergence criteria.
+
+**Risk:** Coupling divergence, debugging complexity.  
+**Mitigation:** Conservative time-step, explicit convergence checks, one golden benchmark.
+
+---
+
+### Sprint 6: Multi-Objective + MDO — pymoo + OpenMDAO (1–2 weeks)
+**Goal:** Pareto optimization across multiple objectives and disciplines.
+
+| Task | Owner | Autonomy | Deliverable |
+|------|-------|----------|-------------|
+| Implement `pymoo_backend.py` | Optimizer → Developer | 🟢 85% | NSGA-II/III alongside Optuna |
+| Pareto front visualization | Post-Processor → Developer | 🟢 90% | Interactive Pareto plots |
+| OpenMDAO integration (if scope allows) | Tech Lead → Developer | 🟡 60% | MDO wiring for multi-discipline |
+| 1 multi-objective demo | Optimizer + Tech Lead | 🟡 70% | Mass vs stress vs temperature Pareto |
+
+**Antoine gate:** Define objective scaling and hard constraints.
+
+---
+
+## 5. Semi-Autonomous Workflow
+
+```
+┌─────────────────────────────────────────────────────────┐
+│                  PER-SPRINT LOOP                         │
+│                                                          │
+│  1. Antoine picks sprint / approves scope        [YOU]   │
+│  2. HQ researches + designs architecture         [AUTO]  │
+│  3. Auditor reviews design for risks             [AUTO]  │
+│  4. Antoine approves architecture (15 min)       [YOU]   │
+│  5. Developer implements + writes tests          [AUTO]  │
+│  6. Auditor reviews code against protocols       [AUTO]  │
+│  7. Antoine validates one benchmark (2-3 hrs)    [YOU]   │
+│  8. Merge → next sprint                          [AUTO]  │
+│                                                          │
+│  Your time: ~2-3 hours/sprint                            │
+│  HQ time: days of implementation/sprint                  │
+└─────────────────────────────────────────────────────────┘
+```
+
+**What runs fully autonomously (steps 2-3, 5-6):**
+- Research tool capabilities, formats, Python bindings
+- Design processor architecture and contract extensions
+- Implement Python adapters, parsers, converters
+- Write and run unit tests against analytical benchmarks
+- Audit code against Atomizer protocols
+- Generate regression reports
+
+**What needs your engineering judgment (steps 1, 4, 7):**
+- Tool priority sequencing (strategic call)
+- Architecture approval (15-min review)
+- Cross-solver parity acceptance (is 5% delta OK?)
+- Benchmark validation (does this match physics?)
+- Geometry quality assessment (does Build123d output look right?)
+
+---
+
+## 6. Quality Gates (Auditor-Defined)
+
+### Per-Processor Gate
+- [ ] Processor implements abstract base class correctly
+- [ ] Round-trip test: contract → native format → solve → parse → contract
+- [ ] At least 1 analytical benchmark passes within tolerance
+- [ ] Unit test coverage ≥ 80% for parser logic
+- [ ] Error handling for: missing files, solver crash, malformed output
+- [ ] Documentation: input/output formats, known limitations
+
+### Per-Sprint Gate
+- [ ] All processor gates pass
+- [ ] Integration test: full pipeline from AtomizerSpec → results
+- [ ] Regression: no existing tests broken
+- [ ] Parity check (if applicable): new solver vs reference solver
+- [ ] Tech Lead sign-off on physics validity
+- [ ] Auditor sign-off on code quality + protocol compliance
+
+### MVP Gate (Sprint 3 Exit)
+- [ ] 3 analytical benchmarks pass (cantilever, plate-hole, modal)
+- [ ] CalculiX vs Nastran parity < 5% stress, < 3% displacement
+- [ ] 50-trial optimization completes unattended
+- [ ] Dual-lane comparison report generates automatically
+- [ ] Antoine validates one real-world study through the new pipeline
+- [ ] All regression tests pass in CI
+
+---
+
+## 7. Risk Register
+
+| # | Risk | Impact | Likelihood | Mitigation | Owner |
+|---|------|--------|------------|------------|-------|
+| R1 | CalculiX vs Nastran parity exceeds tolerance | High | Medium | Start with simple geometries, document element type mapping, investigate mesh sensitivity | Tech Lead |
+| R2 | Gmsh mesh quality on complex geometry | Medium | Medium | Define quality thresholds, add Jacobian/aspect-ratio checks, fallback presets | Tech Lead |
+| R3 | Build123d limitations on complex parametric models | Medium | Low | Start simple, escalate complexity, keep NX lane as fallback | Developer |
+| R4 | Contract design locks in wrong abstractions | High | Low | Freeze contracts only after Sprint 1 validation, allow minor evolution in Sprint 2 | Tech Lead + Auditor |
+| R5 | Package dependency conflicts on T420 | Low | Medium | Use venv or Docker dev environment | IT |
+| R6 | OpenFOAM setup complexity delays Sprint 4 | Medium | High | Docker-first approach, one locked template | IT + Tech Lead |
+| R7 | Scope creep into expansion tools before MVP stable | High | Medium | Hard gate: no Sprint 4+ work until Sprint 3 exit criteria met | Manager + Auditor |
+| R8 | MCP server maintenance burden | Low | Medium | MVP cap at 4 MCP servers, thin wrappers only | MCP Engineer |
+
+---
+
+## 8. Tool Installation Reference
+
+### Sprint 0-2 (Core)
+```bash
+# Python packages
+pip install gmsh pygmsh build123d meshio pyvista
+
+# CalculiX solver
+sudo apt install calculix-ccx
+
+# ParaView (Sprint 3)
+sudo apt install paraview
+```
+
+### Sprint 4+ (Expansion)
+```bash
+# OpenFOAM via Docker
+docker pull openfoam/openfoam-dev
+
+# preCICE
+sudo apt install libprecice-dev python3-precice
+
+# pymoo
+pip install pymoo
+
+# OpenMDAO
+pip install openmdao
+```
+
+---
+
+## 9. Success Metrics
+
+| Metric | Sprint 3 Target | Sprint 6 Target |
+|--------|----------------|----------------|
+| Solver lanes operational | 2 (Nastran + CalculiX) | 4 (+OpenFOAM + coupled) |
+| Optimization trials/hr (bracket-class) | 50+ | 100+ |
+| Analytical benchmarks passing | 3 | 8+ |
+| Cross-solver parity verified | Nastran ↔ CalculiX | + OpenFOAM thermal |
+| Automation level (no human in loop) | 70% | 85% |
+| MCP servers | 2 (CalculiX, Gmsh) | 4 |
+
+---
+
+## 10. Immediate Next Steps
+
+1. **Antoine:** Approve this plan and Sprint 0-1 scope
+2. **IT/Developer:** Run Sprint 0 package installs (est. 1-2 hours)
+3. **Tech Lead:** Finalize contract dataclass specs with field-level detail
+4. **Developer:** Scaffold `atomizer/` package structure
+5. **Auditor:** Prepare benchmark expected-value files for 3 analytical cases
+6. **Manager:** Create Mission Dashboard tasks for Sprint 0 + Sprint 1
+
+---
+
+*This plan is a living document. Update after each sprint retrospective.*