app.py updated

app.py

@@ -33,7 +33,25 @@ app = Flask(
     template_folder='backend/templates'
 )
 app.config['SECRET_KEY'] = 'your-secret-key'
-app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:////tmp/codingo.db'
+#
+# Configure the database connection
+#
+# By default the application wrote its SQLite database into the
+# `/tmp` directory. On local machines this works, but on hosted
+# platforms like Hugging Face Spaces the `/tmp` directory is not
+# persistent across sessions. That means any data stored in
+# `/tmp/codingo.db` would be lost once the process restarts, and
+# newly created user accounts would appear to disappear immediately.
+#
+# To fix this we store the database file inside the project under
+# `backend/instance/codingo.db`. The `backend/instance` directory
+# already exists (it is created by `os.makedirs` below) and is
+# persisted across requests, so user registrations and other data
+# remain available. SQLAlchemy requires three slashes for a relative
+# SQLite URI (e.g. `sqlite:///relative/path.db`). Here we use four
+# leading slashes because the path is relative to the project
+# directory when using `sqlite:///backend/instance/codingo.db`.
+app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///backend/instance/codingo.db'
 app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False
 from flask_wtf.csrf import CSRFProtect