fix:fix total equity zero (#566)

## 📝 Pull Request Template

### 1. Related Issue
Closes # (issue number)

### 2. Type of Change (select one)
Type of Change: Bug Fix 
### 3. Description
Please describe the changes made and why they are necessary.

### 4. Testing
- [x] I have tested this locally.
- [ ] I have updated or added relevant tests.

### 5. Checklist
- [x] I have read the [Code of Conduct](./CODE_OF_CONDUCT.md)
- [x] I have followed the [Contributing Guidelines](./CONTRIBUTING.md)
- [x] My changes follow the project's coding style

Author: su8su

python/valuecell/agents/common/trading/execution/ccxt_trading.py

@@ -1329,8 +1329,10 @@ async def fetch_positions(self, symbols: Optional[List[str]] = None) -> List[Dic
             positions = await exchange.fetch_positions(normalized_symbols)
             return positions
         except Exception as e:
-            print(f"Warning: Could not fetch positions: {e}")
-            return []
+            # Do NOT return an empty list on network/exchange errors; propagate
+            # so upstream retry/backoff logic can kick in and avoid wiping holdings.
+            logger.warning(f"⚠️ Could not fetch positions: {e}")
+            raise
 
     async def cancel_order(self, order_id: str, symbol: str) -> Dict:
         """Cancel an open order.

python/valuecell/agents/common/trading/utils.py

@@ -31,7 +31,10 @@ async def fetch_free_cash_from_gateway(
     logger.info("Fetching exchange balance for LIVE trading mode")
     try:
         if not hasattr(execution_gateway, "fetch_balance"):
-            return 0.0, 0.0
+            raise AttributeError(
+                f"Execution gateway {execution_gateway.__class__.__name__} "
+                "does not implement the required 'fetch_balance' method."
+            )
         balance = await execution_gateway.fetch_balance()
     except Exception as e:
         if retry_cnt < max_retries:
@@ -44,11 +47,12 @@ async def fetch_free_cash_from_gateway(
             return await fetch_free_cash_from_gateway(
                 execution_gateway, symbols, retry_cnt + 1, max_retries
             )
+        # Propagate after exhausting retries so upstream can keep cached portfolio
         logger.error(
-            f"Failed to fetch free cash from exchange after {max_retries} retries, returning 0.0",
+            f"Failed to fetch free cash from exchange after {max_retries} retries.",
             exception=e,
         )
-        return 0.0, 0.0
+        raise
 
     logger.info(f"Raw balance response: {balance}")
     free_map: dict[str, float] = {}
@@ -70,6 +74,10 @@ async def fetch_free_cash_from_gateway(
                 except Exception:
                     continue
 
+    # If balance structure is unrecognized, avoid returning zeros silently
+    if not isinstance(balance, dict) or (not free_map and free_section is None):
+        raise ValueError("Unrecognized balance response shape from exchange")
+
     logger.info(f"Parsed free balance map: {free_map}")
     # Derive quote currencies from symbols, fallback to common USD-stable quotes
     quotes: list[str] = []