fix: flush redis cache on API service startup (#1048)

## Summary
- Flushes all Redis cache on API service startup to avoid
stale/inconsistent responses after catalog updates
- Adds proper lifespan handler to close Redis connection on shutdown

Partial mitigation for #1047.

## Test plan
- [x] Verified cache flush works on restart (set test key, restart, key
is cleared)
- [x] Verified API health and cache health endpoints still work
- [x] Confirmed no external API endpoint exposes the flush functionality

Author: dannon

backend/api/app/core/cache.py

@@ -72,6 +72,16 @@ async def clear_pattern(self, pattern: str) -> int:
             logger.error(f"Cache clear pattern error for {pattern}: {e}")
             return 0
 
+    async def flush_all(self) -> bool:
+        """Flush all keys from the current database"""
+        try:
+            await self.redis.flushdb()
+            logger.info("Cache flushed successfully")
+            return True
+        except redis.RedisError as e:
+            logger.error(f"Cache flush error: {e}")
+            return False
+
     async def get_stats(self) -> Dict[str, Any]:
         """Get cache statistics"""
         try:

backend/api/app/core/dependencies.py

@@ -14,3 +14,9 @@ async def get_cache_service() -> CacheService:
         settings = get_settings()
         _cache_service = CacheService(settings.REDIS_URL)
     return _cache_service
+
+
+def reset_cache_service() -> None:
+    """Reset the global cache service instance (used during shutdown)"""
+    global _cache_service
+    _cache_service = None

backend/api/app/main.py

@@ -1,17 +1,37 @@
+import logging
+from contextlib import asynccontextmanager
+
 from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
 
 from app.api.v1 import cache, health, links, version
 from app.core.config import get_settings
+from app.core.dependencies import get_cache_service, reset_cache_service
 
+logger = logging.getLogger(__name__)
 settings = get_settings()
 
+
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    """Startup and shutdown events for the application"""
+    # Startup: flush cache to ensure fresh data after restart
+    cache_service = await get_cache_service()
+    await cache_service.flush_all()
+    logger.info("Cache cleared on startup")
+    yield
+    # Shutdown: close cache connection and reset singleton
+    await cache_service.close()
+    reset_cache_service()
+
+
 app = FastAPI(
     title="BRC Analytics API",
     version=settings.APP_VERSION,
     openapi_url="/api/openapi.json",
     docs_url="/api/docs",
     redoc_url="/api/redoc",
+    lifespan=lifespan,
 )
 
 app.add_middleware(