feat(CASH): Implement Sign In

[i1skn]

Fixed: APP-3956

Why?

A Cash account only existed on the device that created it. Anyone who reinstalled the app, cleared app data, or picked up a second device had no way back into their account — the Sign In entry point on the deposit intro panel was inert, and the only alternative, Set Up Account, dead-ends on the phone number already being registered.

This closes that hole so an existing account holder can get back to depositing on any device: they enter the phone number attached to the account, approve with their passkey, and land on Add Cash with their linked card already restored.

Approach

Sign-in on a fresh device can't identify the account the usual way, because the user id is exactly what the device is missing. The login ceremony now accepts either identifier — the stored account id, or the phone number — so both entry points share one flow, and the account id recorded by the device comes back from the verified login rather than from local state.

Visuals

Simulator.Screen.Recording.-.iPhone.17.Pro.-.2026-08-07.at.11.27.19.mov

Testing

Requires an existing Cash account with a passkey. To simulate a fresh device, use Developer Settings → Cash Settings → "Clear cash account" — the deposit intro panel reappears with Sign In available.

• Sign In with the phone number on the account: passkey prompt appears, and you land on Add Cash. If the account has a linked card, it shows in the Add From row; if it doesn't, the sheet offers to add a card.
• Sign In with a phone number that has no account: an error shows on the screen and you stay put, able to correct the number.
• Dismiss the passkey prompt mid-flow: the screen returns to editable with no error.
• Back on the sign-in screen closes the flow.

[linear]

APP-3956

[github-actions]

Launch in simulator or device for def031c