Verifies that getLongTermPrivateKey reads the derivation index from vault metadata instead of using hardcoded index 0. Test creates a mock vault with DerivationIndex=5 and confirms the derived key matches index 5.
Verifies that getLongTermPrivateKey reads the derivation index from vault metadata instead of using hardcoded index 0. Test creates a mock vault with DerivationIndex=5 and confirms the derived key matches index 5.