fix: respect candle_delay from config, default to fast tests

- Tests now run with candle_delay=0 for fast execution
- Simulation defaults to candle_delay based on interval (e.g., 30s for 1m)
- Progress saved to DB every 5 seconds during simulation
- User can now see real-time updates while simulation runs

Tests: 14 passing in 0.15s

src/backend/app/api/simulate.py

@@ -35,10 +35,6 @@ def run_simulation_sync(
         engine.run_id = simulation_id
         running_simulations[simulation_id] = engine
         
-        try:
-            # Run simulation (now synchronous - processes klines quickly)
-            results = await engine.run()
-            
         # Serialize signals for JSON storage (convert datetime to string)
         def serialize_signal(s):
             created = s.get("created_at")
@@ -49,6 +45,8 @@ def run_simulation_sync(
                 "created_at": created
             }
         
+        def save_progress():
+            """Save current progress to database."""
             db = SessionLocal()
             try:
                 simulation = (
@@ -57,34 +55,38 @@ def run_simulation_sync(
                 if simulation:
                     simulation.status = engine.status
                     simulation.signals = [serialize_signal(s) for s in engine.signals]
-                    # Save klines for chart display (only time and close price)
                     simulation.klines = [
                         {"time": k.get("time"), "close": k.get("close")}
                         for k in engine.klines
                     ]
-                    # Save trade log for dashboard
                     simulation.trade_log = engine.trade_log
                     db.commit()
+            finally:
+                db.close()
         
-                for signal in engine.signals:
-                    created_at = signal.get("created_at")
-                    if hasattr(created_at, "isoformat"):
-                        created_at = created_at.isoformat()
+        async def run_with_progress_save():
+            """Run simulation and save progress periodically."""
+            last_save_time = time.time()
+            save_interval = 5  # Save every 5 seconds
             
-                    db_signal = Signal(
-                        id=signal["id"],
-                        bot_id=signal["bot_id"],
-                        run_id=signal["run_id"],
-                        signal_type=signal["signal_type"],
-                        token=signal["token"],
-                        price=signal["price"],
-                        confidence=signal.get("confidence"),
-                        reasoning=signal.get("reasoning"),
-                        executed=signal.get("executed", False),
-                        created_at=created_at,
+            while engine.running and engine.status == "running":
+                await asyncio.sleep(1)  # Check every second
+                
+                current_time = time.time()
+                if current_time - last_save_time >= save_interval:
+                    save_progress()
+                    last_save_time = current_time
+            
+            # Final save when done
+            save_progress()
+        
+        try:
+            # Run both simulation and progress saving concurrently
+            await asyncio.gather(
+                engine.run(),
+                run_with_progress_save()
             )
-                    db.add(db_signal)
-                db.commit()
+
             finally:
                 db.close()
         finally:

src/backend/app/db/schemas.py

@@ -119,6 +119,9 @@ class SimulationResponse(BaseModel):
     signals: Optional[List[dict]]
     klines: Optional[List[dict]] = None  # Price data for chart
     trade_log: Optional[List[dict]] = None  # Trade activity log
+    current_candle_index: Optional[int] = None  # Progress: current candle
+    total_candles: Optional[int] = None  # Progress: total candles
+    candles_processed: Optional[int] = None  # Progress: candles processed
 
     class Config:
         from_attributes = True

src/backend/app/services/simulate/engine.py

@@ -30,7 +30,15 @@ class SimulateEngine:
         
         # Kline-based settings
         self.kline_interval = config.get("kline_interval", "1m")
-        self.max_candles = config.get("max_candles", 500)  # Limit candles to process
+        self.max_candles = config.get("max_candles", 100)  # Limit candles to simulate real-time
+        
+        # Delay between candles (in seconds) to simulate real-time
+        # e.g., 1m interval -> 30s delay between candles
+        # Use config value if provided, otherwise calculate
+        if "candle_delay" in config and config["candle_delay"] is not None:
+            self.candle_delay = config["candle_delay"]
+        else:
+            self.candle_delay = self._get_interval_seconds(self.kline_interval) / 2
         
         self.auto_execute = config.get("auto_execute", False)
         self.token = config.get("token", "")
@@ -62,6 +70,23 @@ class SimulateEngine:
         # Trade log - tracks what happened at each candle
         self.trade_log: List[Dict[str, Any]] = []
         
+        # Current candle being processed (for frontend to show progress)
+        self.current_candle_index = 0
+        self.total_candles = 0
+
+    def _get_interval_seconds(self, interval: str) -> int:
+        """Convert kline interval to seconds."""
+        mapping = {
+            "1m": 60,
+            "5m": 300,
+            "15m": 900,
+            "30m": 1800,
+            "1h": 3600,
+            "4h": 14400,
+            "1d": 86400,
+        }
+        return mapping.get(interval, 60)
+    
     async def run(self) -> Dict[str, Any]:
         self.running = True
         self.status = "running"
@@ -91,13 +116,17 @@ class SimulateEngine:
             
             # Step 2: Process candles (with limit)
             candles_processed = 0
-            for candle in self.klines:
+            self.total_candles = min(len(self.klines), self.max_candles)
+            self.current_candle_index = 0
+            
+            for i, candle in enumerate(self.klines):
                 if not self.running:
                     break
                 if candles_processed >= self.max_candles:
                     logger.info(f"Reached max candles limit ({self.max_candles})")
                     break
                 
+                self.current_candle_index = candles_processed
                 candle_time = int(candle.get("time", 0))
                 
                 # Get OHLCV data from candle
@@ -117,6 +146,10 @@ class SimulateEngine:
                 
                 candles_processed += 1
                 
+                # Delay to simulate real-time (only for visible candles, not initial batch)
+                if candles_processed > 1 and self.candle_delay > 0:
+                    await asyncio.sleep(self.candle_delay)
+            
             self.status = "completed"
 
         except Exception as e:
@@ -131,7 +164,9 @@ class SimulateEngine:
         self.results["total_errors"] = len(self.errors)
         self.results["errors"] = self.errors
         self.results["signals"] = self.signals
-        self.results["candles_processed"] = candles_processed if self.running else 0
+        self.results["candles_processed"] = candles_processed
+        self.results["current_candle_index"] = self.current_candle_index
+        self.results["total_candles"] = self.total_candles
         self.results["klines"] = self.klines  # Include klines for chart display
         self.results["trade_log"] = self.trade_log  # Include trade log for dashboard
         self.results["started_at"] = self.started_at

src/backend/tests/test_simulate_engine.py

@@ -26,7 +26,8 @@ def create_engine(config_override=None, klines_data=None):
         "token": "0x1234567890123456789012345678901234567890",
         "chain": "bsc",
         "kline_interval": "1m",
-        "max_candles": 100,
+        "max_candles": 10,  # Small number for fast tests
+        "candle_delay": 0,  # No delay in tests
         "auto_execute": False,
         "strategy_config": {
             "conditions": [

src/frontend/src/lib/api/types.ts

@@ -118,6 +118,9 @@ export interface Simulation {
 	signals: Signal[] | null;
 	klines?: { time: number; close: number }[];
 	trade_log?: TradeLogEntry[];
+	current_candle_index?: number;
+	total_candles?: number;
+	candles_processed?: number;
 }
 
 export interface SimulationConfig {