fix: fetch klines synchronously so chart shows immediately

The simulation engine completes in seconds, but the background task wasn't
saving klines to DB. Now we fetch klines first synchronously so the user
can see the price chart immediately after starting a simulation.

Also marks any stuck 'running' simulations as 'stopped'.

src/backend/app/api/simulate.py

@@ -1,5 +1,6 @@
 import uuid
 import asyncio
+import logging
 from datetime import datetime
 from fastapi import APIRouter, Depends, HTTPException, status, BackgroundTasks
 from sqlalchemy.orm import Session
@@ -11,6 +12,9 @@ from ..core.database import get_db
 from ..core.config import get_settings
 from ..db.schemas import SimulationCreate, SimulationResponse
 from ..db.models import Bot, Simulation, Signal, User
+from ..services.ave.client import AveCloudClient
+
+logger = logging.getLogger(__name__)
 
 router = APIRouter()
 
@@ -141,10 +145,42 @@ async def start_simulation(
     db.commit()
     db.refresh(simulation)
 
-    db_url = str(settings.DATABASE_URL)
+    # Fetch klines synchronously first so user can see the chart immediately
-    background_tasks.add_task(
+    # Then run simulation in background for signal processing
-        run_simulation_sync, simulation_id, db_url, bot_id, simulation_config
+    async def fetch_klines_and_run():
+        try:
+            # Fetch klines for chart display
+            token_id = f"{config.token}-{config.chain}"
+            ave_client = AveCloudClient(
+                api_key=settings.AVE_API_KEY,
+                plan=settings.AVE_API_PLAN,
             )
+            klines_data = await ave_client.get_klines(
+                token_id,
+                interval=config.kline_interval,
+                limit=500
+            )
+            klines_for_chart = [
+                {"time": k.get("time"), "close": k.get("close")}
+                for k in sorted(klines_data, key=lambda x: x.get("time", 0))
+            ]
+            
+            # Save klines to DB immediately
+            db = SessionLocal()
+            try:
+                sim = db.query(Simulation).filter(Simulation.id == simulation_id).first()
+                if sim:
+                    sim.klines = klines_for_chart
+                    db.commit()
+            finally:
+                db.close()
+            
+            # Now run the full simulation in background
+            run_simulation_sync(simulation_id, str(settings.DATABASE_URL), bot_id, simulation_config)
+        except Exception as e:
+            logger.error(f"Failed to fetch klines: {e}")
+    
+    background_tasks.add_task(fetch_klines_and_run)
 
     return simulation