A kdbx vault acts as a key

The idea, if properly implemented, makes it possible to transport key and vault files in the same usb storage, securely.

The idea is this:

I create a new database (A) protected only by password and inside I place a key file.

To open the real database (B) I place B in the "vault" field and A in the "key" field. They are both vaults, but one contains only the key (A).

When I press Open the vault that acts as the key will pop up a password prompt to get access to its database. Once the password is entered, database B goes looking for the key file to open its vault.

Advantages of this scheme:

I can carry key file and safe in the usb dongle.
If I am crossing a (potentially dangerous) border I have the option) to remember only one password that the vault that contains the real key.

No files or tests are identified in the issue. Start by tracing KeePassDX's vault-opening and key-file handling entry points, then determine how a kdbx vault supplied as the key should be unlocked and reused. Done means the described A/B flow works securely, including the password prompt and subsequent key lookup.

Written by the indexing model from the issue text.