Clarify settings and app wiring

app/backend/main.py

@@ -1,19 +1,28 @@
-"""Application entrypoint and router wiring."""
+"""
+API Application Entrypoint and Router Wiring.
+
+This module initializes the core FastAPI application instance, loads
+configuration, applies middleware, and wires up all defined API routers.
+"""
 
 from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
-
+from typing import List
 
 from api.v1.router import router as api_v1_router
 from operations.health.router import router as health_router
+from core.config import get_settings, Settings # Import Settings type for clarity
 
-from core.config import get_settings
+def create_app(settings: Settings = get_settings()) -> FastAPI:
+    """
+    Create and configure the FastAPI application instance.
 
-def create_app() -> FastAPI:
-    """Create and configure the FastAPI application."""
-
-    settings = get_settings()
+    Args:
+        settings: Configuration object from core.config. Defaults to current settings.
 
+    Returns:
+        A configured FastAPI application instance.
+    """
     app = FastAPI(
         title=settings.title,
         description=settings.description,
@@ -23,19 +32,25 @@ def create_app() -> FastAPI:
         openapi_url="/openapi.json",
     )
 
-    # CORS for local dev (frontend on 3000). Tighten/override in prod.
+    # Define allowed origins dynamically based on local dev environment needs
+    # In a production setting, this list would typically be sourced from environment variables.
+    allowed_origins: List[str] = ["http://localhost:3000", "http://127.0.0.1:3000"]
+    
+    # Configure CORS middleware
+    # TODO: Tightly restrict origins in production deployment.
     app.add_middleware(
         CORSMiddleware,
-        allow_origins=["http://localhost:3000", "http://127.0.0.1:3000"],
+        allow_origins=allowed_origins,
         allow_credentials=True,
         allow_methods=["*"],
         allow_headers=["*"],
     )
 
+    # Include API routers
     app.include_router(health_router)
     app.include_router(api_v1_router, prefix="/api/v1")
 
     return app
 
-
+# Main entry point for services like Uvicorn (e.g., `uvicorn main:app --reload`)
 app = create_app()