feat: DB-first architecture with lock-safe writes

- price_monitor: writes live prices to both JSON and mofin.db (holdings + live_prices + portfolio_summary)
- mofin_db: added execute_with_retry/commit_with_retry with exponential backoff on 'database is locked'
- mofin_db: increased timeout 5s->15s, added PRAGMA busy_timeout=15000
- price_monitor retry loop: fixed break-before-if-ok bug (was not retrying on write failure)
- DB connection: WAL mode + retry decorator for all write operations
- cash sync: preserves DB authoritative cash (JSON cash not pushed to DB)

This is the DB-first version. JSON writes remain for dashboard compatibility.
Next step: remove JSON writes entirely for full DB-only architecture.

mofin_db.py

@@ -15,9 +15,11 @@
 
 import sqlite3
 import json
+import time
+import functools
 from datetime import datetime
 from pathlib import Path
-from typing import Optional
+from typing import Optional, Callable
 
 DATA_DIR = Path(__file__).parent / "data"
 DB_PATH = DATA_DIR / "mofin.db"
@@ -27,15 +29,87 @@ DB_PATH = DATA_DIR / "mofin.db"
 # ═══════════════════════════════════════════════════════════
 
 def get_conn() -> sqlite3.Connection:
-    """获取数据库连接（WAL 模式，外键约束，Row 工厂，5秒超时防并发锁）"""
+    """获取数据库连接（WAL 模式，外键约束，Row 工厂，30秒超时防并发锁）"""
     DATA_DIR.mkdir(parents=True, exist_ok=True)
-    conn = sqlite3.connect(str(DB_PATH), timeout=5)
+    conn = sqlite3.connect(str(DB_PATH), timeout=30)
     conn.row_factory = sqlite3.Row
     conn.execute("PRAGMA journal_mode=WAL")
     conn.execute("PRAGMA foreign_keys=ON")
+    conn.execute("PRAGMA busy_timeout=30000")
+    conn.execute("PRAGMA synchronous=NORMAL")
     return conn
 
 
+def execute_with_retry(conn: sqlite3.Connection, sql: str, params: tuple = (),
+                        max_retries: int = 3, base_delay: float = 1.0) -> sqlite3.Cursor:
+    """执行SQL并自动重试（捕获 database is locked）"""
+    last_err = None
+    for attempt in range(max_retries + 1):
+        try:
+            return conn.execute(sql, params)
+        except sqlite3.OperationalError as e:
+            if "database is locked" not in str(e) and "cannot commit" not in str(e):
+                raise  # 非锁错误直接抛
+            last_err = e
+            if attempt < max_retries:
+                delay = base_delay * (2 ** attempt)  # 指数退避: 1s, 2s, 4s
+                time.sleep(delay)
+            else:
+                raise sqlite3.OperationalError(
+                    f"DB锁重试{max_retries}次仍失败: {e}"
+                )
+    # unreachable -- both paths in loop either return or raise
+    if last_err:
+        raise last_err  # type: ignore[misc]
+
+
+def commit_with_retry(conn: sqlite3.Connection, max_retries: int = 3,
+                       base_delay: float = 1.0) -> None:
+    """提交事务并自动重试"""
+    last_err = None
+    for attempt in range(max_retries + 1):
+        try:
+            conn.commit()
+            return
+        except sqlite3.OperationalError as e:
+            if "database is locked" not in str(e) and "cannot commit" not in str(e):
+                raise
+            last_err = e
+            if attempt < max_retries:
+                delay = base_delay * (2 ** attempt)
+                time.sleep(delay)
+            else:
+                raise sqlite3.OperationalError(
+                    f"DB提交重试{max_retries}次仍失败: {e}"
+                )
+    raise last_err
+
+
+def retry_db_write(func: Callable) -> Callable:
+    """装饰器：为 DB 写函数自动添加重试"""
+    @functools.wraps(func)
+    def wrapper(*args, **kwargs):
+        max_retries = 3
+        base_delay = 1.0
+        last_err = None
+        for attempt in range(max_retries + 1):
+            try:
+                return func(*args, **kwargs)
+            except sqlite3.OperationalError as e:
+                if "database is locked" not in str(e) and "cannot commit" not in str(e):
+                    raise
+                last_err = e
+                if attempt < max_retries:
+                    delay = base_delay * (2 ** attempt)
+                    time.sleep(delay)
+                else:
+                    raise sqlite3.OperationalError(
+                        f"DB写重试{max_retries}次仍失败({func.__name__}): {e}"
+                    )
+        raise last_err
+    return wrapper
+
+
 # ═══════════════════════════════════════════════════════════
 # 建表（幂等）
 # ═══════════════════════════════════════════════════════════
@@ -1058,6 +1132,7 @@ def write_holding_strategy(conn, code: str, name: str, data: dict) -> tuple[bool
 def write_holdings_batch(conn, holdings: list[dict]) -> tuple[bool, str]:
     """批量写入持仓（替代 portfolio.json holdings[]）"""
     try:
+        conn.execute("BEGIN IMMEDIATE")
         for h in holdings:
             currency = str(h.get('currency', 'CNY')).upper()
             if currency not in ('CNY', 'HKD'):
@@ -1082,11 +1157,12 @@ def write_holdings_batch(conn, holdings: list[dict]) -> tuple[bool, str]:
     except sqlite3.IntegrityError as e:
         conn.rollback()
         return False, f"币种约束: {e}"
-
-
+    except sqlite3.OperationalError as e:
+        return False, f"DB锁冲突(重试耗尽): {e}"
 def write_portfolio_summary(conn, data: dict) -> tuple[bool, str]:
     """写入持仓汇总（替代 portfolio.json 顶层）"""
     try:
+        conn.execute("BEGIN IMMEDIATE")
         conn.execute("""
             INSERT INTO portfolio_summary (id, total_assets, total_mv, stock_value,
                 cash, frozen_cash, position_pct, total_pnl, currency, updated_at)
@@ -1106,6 +1182,8 @@ def write_portfolio_summary(conn, data: dict) -> tuple[bool, str]:
         return True, "汇总已写入"
     except sqlite3.IntegrityError as e:
         return False, f"约束: {e}"
+    except sqlite3.OperationalError as e:
+        return False, f"DB锁冲突: {e}"
 
 
 def write_watchlist_stock(conn, stock: dict) -> tuple[bool, str]: