fix: add session lock in StockSelector, remove unused HEALTH_PORT_OFFSET, lint fixesHEADmaster

- Add asyncio.Lock to StockSelector._ensure_session() to prevent race condition
- Remove unused HEALTH_PORT_OFFSET constant from news-collector
- Auto-fix import sorting and formatting from ruff

1 files changed, 6 insertions, 3 deletions

diff --git a/services/strategy-engine/src/strategy_engine/stock_selector.py b/services/strategy-engine/src/strategy_engine/stock_selector.py
index 5acef0f..8657b93 100644
--- a/services/strategy-engine/src/strategy_engine/stock_selector.py
+++ b/services/strategy-engine/src/strategy_engine/stock_selector.py
@@ -1,5 +1,6 @@
 """3-stage stock selector engine: sentiment → technical → LLM."""
 
+import asyncio
 import json
 import logging
 import re
@@ -218,11 +219,13 @@ class StockSelector:
         self._model = anthropic_model
         self._max_picks = max_picks
         self._http_session: aiohttp.ClientSession | None = None
+        self._session_lock = asyncio.Lock()
 
     async def _ensure_session(self) -> aiohttp.ClientSession:
-        if self._http_session is None or self._http_session.closed:
-            self._http_session = aiohttp.ClientSession()
-        return self._http_session
+        async with self._session_lock:
+            if self._http_session is None or self._http_session.closed:
+                self._http_session = aiohttp.ClientSession()
+            return self._http_session
 
     async def close(self) -> None:
         if self._http_session and not self._http_session.closed: