## ADDED Requirements

### Requirement: Silent 19-digit ICCID verification retry

When an asset login identifier matches `^89\\d{17}$`, the H5 client SHALL first verify the entered 19-digit value. If that attempt fails or does not return a non-empty `asset_token`, it SHALL calculate the ISO/IEC 7812 Luhn mod-10 check digit, append it as the twentieth digit, and verify the completed ICCID exactly once.

#### Scenario: Completed ICCID succeeds

- **WHEN** a customer enters a 19-digit numeric identifier beginning with `89`
- **AND** the initial verification does not provide an asset token
- **AND** verification of the Luhn-completed 20-digit ICCID returns an asset token
- **THEN** the customer continues through login without seeing an error from the first verification
- **AND** the authenticated session uses the 20-digit ICCID

#### Scenario: Initial verification succeeds

- **WHEN** a customer enters a 19-digit numeric identifier beginning with `89`
- **AND** initial verification returns an asset token
- **THEN** the client SHALL not calculate or submit a second identifier

#### Scenario: Completed ICCID fails

- **WHEN** the Luhn-completed retry does not return an asset token
- **THEN** the client SHALL invoke the existing login failure presentation once using the retry failure

#### Scenario: Identifier is not a 19-digit ICCID prefix

- **WHEN** an identifier does not match `^89\\d{17}$`
- **AND** verification fails or does not return an asset token
- **THEN** the client SHALL not issue a retry
- **AND** SHALL retain the existing login failure presentation