PhoneNumberField still decomposes only four seeded dial codes

[marassteiner]

Summary

PR #909 opened the prefix input to any 1–3 digit dial code, but seeded-value decomposition still walks a closed list of four codes (+41, +49, +43, +423) and falls back to +41 plus an empty national field for everything else. A stored +33…, +1…, +7…, or +420… number is therefore still shown as 41 with a blank number; the user has to re-type the whole number before submit.

Found while reviewing #909. Not a merge-blocker: this is the pre-existing seed path, now improved for +43 / +423. New input of any 1–3 digit prefix already works. The PR body explicitly rejected a full country-code picker.

Evidence

• lib/widgets/form/phone_number_field.dart:18 — final prefixes = ['+41', '+49', '+43', '+423'];
• lib/widgets/form/phone_number_field.dart:28-34 — longest-first match only against that list
• lib/widgets/form/phone_number_field.dart:42 — prefix ??= prefixes.first; (+41)
• test/screens/kyc/steps/kyc_personal_data_page_test.dart:178-183 — pins the +336… → displayed 41 fallback
• Call sites that seed from the API and later submit phoneCtrl.value: lib/screens/kyc/steps/personal_data/kyc_personal_data_page.dart:140, registration personal step

Suggested follow-up

• Decompose seeded values with a complete, longest-first calling-code table used only for split-on-prefill, never as an input allow-list (CONTRIBUTING: the API decides whether a dial code exists).
• Or have the API return prefix and national number separately so the client does not guess.
• Add prefill tests for +1, +7, and an unknown 2-/3-digit code.

Related

• feat(kyc): open the phone country prefix field to any 1-3 digit dial code #909