@mytec: feat: Phase 3.0 Architecture Refactor ✅

Major refactoring of RFCP backend:
- Modular propagation models (8 models)
- SharedMemoryManager for terrain data
- ProcessPoolExecutor parallel processing
- WebSocket progress streaming
- Building filtering pipeline (351k → 15k)
- 82 unit tests

Performance: Standard preset 38s → 5s (7.6x speedup)

Known issue: Detailed preset timeout (fix in 3.1.0)

backend/app/api/routes/system.py

@@ -46,15 +46,29 @@ async def get_system_info():
     }
 
 
+@router.get("/models")
+async def get_propagation_models():
+    """Return available propagation models and their valid ranges."""
+    from app.core.engine import engine
+    return {
+        "models": engine.get_available_models(),
+    }
+
+
 @router.post("/shutdown")
 async def shutdown():
-    """Graceful shutdown endpoint. Kills worker processes and exits."""
+    """Graceful shutdown endpoint. Kills worker processes then self-terminates.
+
+    Electron calls this first, waits briefly, then does PID-tree kill.
+    The os._exit(3s) is a safety net in case Electron doesn't kill us.
+    """
     from app.services.parallel_coverage_service import _kill_worker_processes
 
     killed = _kill_worker_processes()
 
-    # Schedule hard exit after response is sent
-    loop = asyncio.get_event_loop()
-    loop.call_later(0.5, lambda: os._exit(0))
+    # Safety net: self-terminate after 3s if Electron doesn't kill us.
+    # Delay is long enough for Electron to do PID-tree kill first (preferred).
+    loop = asyncio.get_running_loop()
+    loop.call_later(3.0, lambda: os._exit(0))
 
     return {"status": "shutting down", "workers_killed": killed}