Fix: lifespan teardown masks startup failures

backend/src/infrastructure/app_factory.py

@@ -53,15 +53,24 @@ async def lifespan(app: FastAPI) -> AsyncGenerator[None, None]:
 
         await set_threadpool_tokens()
 
+        # Teardown must only close what actually initialized: when startup fails
+        # midway, closing a never-initialized component raises from the finally
+        # block and masks the real startup error (e.g. an unreachable DB was
+        # reported as "Backend 'redis' is not available" from close_cache).
+        cache_initialized = False
+        rate_limiter_initialized = False
+
         try:
             if isinstance(settings, DatabaseSettings) and create_tables_on_startup:
                 await create_tables()
 
             if isinstance(settings, CacheSettings) and settings.CACHE_ENABLED:
                 await initialize_cache()
+                cache_initialized = True
 
             if isinstance(settings, RateLimiterSettings) and settings.RATE_LIMITER_ENABLED:
                 await initialize_rate_limiter()
+                rate_limiter_initialized = True
 
             await auth.initialize()
 
@@ -72,10 +81,10 @@ async def lifespan(app: FastAPI) -> AsyncGenerator[None, None]:
         finally:
             await auth.shutdown()
 
-            if isinstance(settings, CacheSettings) and settings.CACHE_ENABLED:
+            if cache_initialized:
                 await close_cache()
 
-            if isinstance(settings, RateLimiterSettings) and settings.RATE_LIMITER_ENABLED:
+            if rate_limiter_initialized:
                 await close_rate_limiter()
 
     return lifespan

backend/tests/unit/infrastructure/test_app_factory.py

@@ -0,0 +1,29 @@
+"""Unit tests for the application lifespan factory."""
+
+import pytest
+from fastapi import FastAPI
+
+from src.infrastructure import app_factory
+from src.infrastructure.config.settings import settings
+
+
+@pytest.mark.asyncio
+async def test_startup_failure_surfaces_the_original_error(monkeypatch):
+    """A failed startup must raise the failing step's exception, not a teardown one.
+
+    Before the initialized-flags guard, a startup failure (e.g. an unreachable DB
+    in ``create_tables``) reached the ``finally`` block, where ``close_cache()``
+    raised ``BackendNotFoundError`` for the never-initialized backend and masked
+    the real error at the bottom of the log.
+    """
+
+    async def failing_create_tables() -> None:
+        raise RuntimeError("db unreachable")
+
+    monkeypatch.setattr(app_factory, "create_tables", failing_create_tables)
+
+    lifespan = app_factory.lifespan_factory(settings, create_tables_on_startup=True)
+
+    with pytest.raises(RuntimeError, match="db unreachable"):
+        async with lifespan(FastAPI()):
+            pass  # pragma: no cover - startup fails before the yield