Number field disappears from username selector when invalid username is entered

[cyberstream]

• I have searched open and closed issues for duplicates
• I am submitting a bug report for existing functionality that does not work as intended
• I have read https://github.com/signalapp/Signal-Android/wiki/Submitting-useful-bug-reports
• This isn't a feature request or a discussion topic

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Bug description

When selecting a new username, if an invalid number is entered for the username (e.g. already in use), the number field disappears.

Steps to reproduce

• Open Settings > Profile Picture > Username.
• Enter a username, e.g. "John".
• App will propose a numeric extension that is available.
• Delete the automatically generated number.
• Enter a number already in use, e.g. "10".
• App displays error message: "This username is not available, try another number."

Actual result: Number field disappears from username selector. In order to get the number field to return, user must enter a different base username (the text portion) that is available, or, if user wants to keep the same base username as they started with (e.g. "John"), they must leave the username page and come back to it to get the number field to appear again.

Expected result: App should indicate the proposed numeric extension to the username is not available by some other means, such as turning it red and displaying the error message below the username selector. The number field should never be removed.

Screenshots

Device info

Device: Samsung SM-918U (Galaxy S23 Ultra)
Android version: 14
Signal version: 7.15.4

Link to debug log

Debug Log