Add Account dialog defaults to existing Account #0 without warning, causing derivation path duplicates

[Sponge5663]

Describe the bug
When adding a new account to an existing singlesig wallet, the "Add Account" dialog defaults to "Account #0" even if Account #0 already exists. If the user clicks OK without manually changing the dropdown, Sparrow imports the xpub for Account #0 again, creating a duplicate derivation path under a new tab name. This corrupts the wallet's transaction mapping and splits history between tabs.

To Reproduce
Steps to reproduce the behavior:

1. Create a wallet with Account #0 (e.g., Native Segwit)
2. Add Account #1, give it a name
3. Click "Add Account..." again
4. Dialog shows "Account #0" as the default option
5. Click OK without changing the dropdown
6. Sparrow creates a new tab with the same derivation path as Account #0
7. Transaction history becomes split/corrupted across tabs

Expected behavior
The "Add Account" dialog should either:

• Default to the next unused account number (e.g., Account #2 if #0 and #1 exist

), OR

• Gray out/disable already-used account numbers, OR
• Show a warning if the user selects an already-used account

Screenshots
[Screenshot showing Account #0 offered when it already exists]
)
Sparrow Version: 2.5.1
OS: macOS / Linux Mint

[craigraw]

I've following the steps to reproduce multiple times, and I can't reproduce the issue you have described. Sparrow excludes already added accounts in the Add Account dialog.

Perhaps you are using a non-default derivation path, so Sparrow can't detect what accounts have already been added?