feat: Daily 모드 ConnectionError 재시도 로직 추가 (issue #209)

- _retry_connection() 헬퍼 추가: MAX_CONNECTION_RETRIES(3회) 지수 백오프
  (2^attempt 초) 재시도, 읽기 전용 API 호출에만 적용 (주문 제외)
- run_daily_session(): get_current_price / get_overseas_price 호출에 적용
- run_daily_session(): get_balance / get_overseas_balance 호출에 적용
  - 잔고 조회 전체 실패 시 해당 마켓을 skip하고 다른 마켓은 계속 처리
- 테스트 5개 추가: TestRetryConnection 클래스

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/main.py

@@ -88,6 +88,47 @@ DAILY_TRADE_SESSIONS = 4  # Number of trading sessions per day
 TRADE_SESSION_INTERVAL_HOURS = 6  # Hours between sessions
 
 
+async def _retry_connection(coro_factory: Any, *args: Any, label: str = "", **kwargs: Any) -> Any:
+    """Call an async function retrying on ConnectionError with exponential backoff.
+
+    Retries up to MAX_CONNECTION_RETRIES times (exclusive of the first attempt),
+    sleeping 2^attempt seconds between attempts.  Use only for idempotent read
+    operations — never for order submission.
+
+    Args:
+        coro_factory: Async callable (method or function) to invoke.
+        *args: Positional arguments forwarded to coro_factory.
+        label: Human-readable label for log messages.
+        **kwargs: Keyword arguments forwarded to coro_factory.
+
+    Raises:
+        ConnectionError: If all retries are exhausted.
+    """
+    for attempt in range(1, MAX_CONNECTION_RETRIES + 1):
+        try:
+            return await coro_factory(*args, **kwargs)
+        except ConnectionError as exc:
+            if attempt < MAX_CONNECTION_RETRIES:
+                wait_secs = 2 ** attempt
+                logger.warning(
+                    "Connection error %s (attempt %d/%d), retrying in %ds: %s",
+                    label,
+                    attempt,
+                    MAX_CONNECTION_RETRIES,
+                    wait_secs,
+                    exc,
+                )
+                await asyncio.sleep(wait_secs)
+            else:
+                logger.error(
+                    "Connection error %s — all %d retries exhausted: %s",
+                    label,
+                    MAX_CONNECTION_RETRIES,
+                    exc,
+                )
+                raise
+
+
 def _extract_symbol_from_holding(item: dict[str, Any]) -> str:
     """Extract symbol from overseas holding payload variants."""
     for key in (
@@ -964,11 +1005,18 @@ async def run_daily_session(
             try:
                 if market.is_domestic:
                     current_price, price_change_pct, foreigner_net = (
-                        await broker.get_current_price(stock_code)
+                        await _retry_connection(
+                            broker.get_current_price,
+                            stock_code,
+                            label=stock_code,
+                        )
                     )
                 else:
-                    price_data = await overseas_broker.get_overseas_price(
-                        market.exchange_code, stock_code
+                    price_data = await _retry_connection(
+                        overseas_broker.get_overseas_price,
+                        market.exchange_code,
+                        stock_code,
+                        label=f"{stock_code}@{market.exchange_code}",
                     )
                     current_price = safe_float(
                         price_data.get("output", {}).get("last", "0")
@@ -1019,9 +1067,27 @@ async def run_daily_session(
             logger.warning("No valid stock data for market %s", market.code)
             continue
 
-        # Get balance data once for the market
+        # Get balance data once for the market (read-only — safe to retry)
+        try:
+            if market.is_domestic:
+                balance_data = await _retry_connection(
+                    broker.get_balance, label=f"balance:{market.code}"
+                )
+            else:
+                balance_data = await _retry_connection(
+                    overseas_broker.get_overseas_balance,
+                    market.exchange_code,
+                    label=f"overseas_balance:{market.exchange_code}",
+                )
+        except ConnectionError as exc:
+            logger.error(
+                "Balance fetch failed for market %s after all retries — skipping market: %s",
+                market.code,
+                exc,
+            )
+            continue
+
         if market.is_domestic:
-            balance_data = await broker.get_balance()
             output2 = balance_data.get("output2", [{}])
             total_eval = safe_float(
                 output2[0].get("tot_evlu_amt", "0")
@@ -1033,7 +1099,6 @@ async def run_daily_session(
                 output2[0].get("pchs_amt_smtl_amt", "0")
             ) if output2 else 0
         else:
-            balance_data = await overseas_broker.get_overseas_balance(market.exchange_code)
             output2 = balance_data.get("output2", [{}])
             if isinstance(output2, list) and output2:
                 balance_info = output2[0]

tests/test_main.py

@@ -18,6 +18,7 @@ from src.main import (
     _extract_held_codes_from_balance,
     _extract_held_qty_from_balance,
     _handle_market_close,
+    _retry_connection,
     _run_context_scheduler,
     _run_evolution_loop,
     _start_dashboard_server,
@@ -3183,3 +3184,90 @@ class TestOverseasBrokerIntegration:
 
         # DB도 브로커도 보유 없음 → BUY 주문이 실행되어야 함 (회귀 테스트)
         overseas_broker.send_overseas_order.assert_called_once()
+
+
+# ---------------------------------------------------------------------------
+# _retry_connection — unit tests (issue #209)
+# ---------------------------------------------------------------------------
+
+
+class TestRetryConnection:
+    """Unit tests for the _retry_connection helper (issue #209)."""
+
+    @pytest.mark.asyncio
+    async def test_success_on_first_attempt(self) -> None:
+        """Returns the result immediately when the first call succeeds."""
+        async def ok() -> str:
+            return "data"
+
+        result = await _retry_connection(ok, label="test")
+        assert result == "data"
+
+    @pytest.mark.asyncio
+    async def test_succeeds_after_one_connection_error(self) -> None:
+        """Retries once on ConnectionError and returns result on 2nd attempt."""
+        call_count = 0
+
+        async def flaky() -> str:
+            nonlocal call_count
+            call_count += 1
+            if call_count < 2:
+                raise ConnectionError("timeout")
+            return "ok"
+
+        with patch("src.main.asyncio.sleep") as mock_sleep:
+            mock_sleep.return_value = None
+            result = await _retry_connection(flaky, label="flaky")
+
+        assert result == "ok"
+        assert call_count == 2
+        mock_sleep.assert_called_once()
+
+    @pytest.mark.asyncio
+    async def test_raises_after_all_retries_exhausted(self) -> None:
+        """Raises ConnectionError after MAX_CONNECTION_RETRIES attempts."""
+        from src.main import MAX_CONNECTION_RETRIES
+
+        call_count = 0
+
+        async def always_fail() -> None:
+            nonlocal call_count
+            call_count += 1
+            raise ConnectionError("unreachable")
+
+        with patch("src.main.asyncio.sleep") as mock_sleep:
+            mock_sleep.return_value = None
+            with pytest.raises(ConnectionError, match="unreachable"):
+                await _retry_connection(always_fail, label="always_fail")
+
+        assert call_count == MAX_CONNECTION_RETRIES
+
+    @pytest.mark.asyncio
+    async def test_passes_args_and_kwargs_to_factory(self) -> None:
+        """Forwards positional and keyword arguments to the callable."""
+        received: dict = {}
+
+        async def capture(a: int, b: int, *, key: str) -> str:
+            received["a"] = a
+            received["b"] = b
+            received["key"] = key
+            return "captured"
+
+        result = await _retry_connection(capture, 1, 2, key="val", label="test")
+        assert result == "captured"
+        assert received == {"a": 1, "b": 2, "key": "val"}
+
+    @pytest.mark.asyncio
+    async def test_non_connection_error_not_retried(self) -> None:
+        """Non-ConnectionError exceptions propagate immediately without retry."""
+        call_count = 0
+
+        async def bad_input() -> None:
+            nonlocal call_count
+            call_count += 1
+            raise ValueError("bad data")
+
+        with pytest.raises(ValueError, match="bad data"):
+            await _retry_connection(bad_input, label="bad")
+
+        assert call_count == 1  # No retry for non-ConnectionError