Set up default currency accounts automatically (#72)

docs/ux/exchange-workspace.md

@@ -302,32 +302,42 @@ that contradicts displayed balances or usage without explaining the fixtures.
 - Keep unrelated accounts/history accessible during a pending operation. Do not
   block the whole product behind an exchange spinner.
 
-## Empty currency accounts (task #66)
+## Automatic currency accounts (task #72)
 
-The shared empty-account message used on Accounts and transfer screens explains
-that no currency accounts have been set up and directs the customer to support
-to request setup. English and Russian no longer suggest that refreshing creates
-accounts or imply that automatic provisioning is underway. This follows the
-existing support guidance for missing funding and payout setup. The application
-has no configured support contact channel; the message therefore provides text
-guidance without a nonfunctional contact button or invented contact details.
+New customers receive RUB, USDT and USDC accounts through backend-owned setup
+during signup. Existing customers receive missing defaults on their next wallet
+load. The UI requires no account-creation form or support contact. During initial
+loading it announces that the accounts are being prepared. Failure shows one
+clear load error and a **Try again** action that reruns the same idempotent setup.
+An unexpected empty snapshot has its own setup-failure fallback, rather than
+being shown simultaneously with an error. A failed refresh retains existing
+cards and the stale-data warning. Account-not-found copy requires loaded data.
 
-UX review: the copy names the missing resource and the next step, retains the
-existing wrapping text and accessible reading order, and does not alter loading,
-error or populated-state behavior. Existing manual refresh remains available for
-accounts provisioned externally. This copy-only change adds no controls or
-journey outcomes and requires no new analytics events. Existing transaction
-journey signals and their production measurement limitations below still apply;
-support resolution and external account provisioning are not measured in-app.
+The existing DTO → mapper → service → model → provider → UI boundaries remain
+intact. Account creation belongs to the backend/provider, and widgets invoke the
+existing provider refresh action. English and Russian use wrapping text and the
+existing accessible button pattern; status text uses a live region. Dedicated
+widget regressions cover loading, failure, retry and successful default accounts
+on Accounts, Top up, Exchange and Payout at 320px with 1.6× text. Native device and
+screen-reader QA remain a release check; tests do not claim physical-device QA.
 
-Validation: `flutter gen-l10n`, `flutter analyze` in `frontend/app`,
-`make test-frontend` (217 tests), and `git diff --check` passed. No Dart source
-changed, so Dart formatting was not applicable. Existing responsive workspace
-tests cover Russian at 320px with enlarged text; this copy-only change does not
-add a dedicated empty-state rendering or native screen-reader test. No security
-scan was requested. Delivery: [task #66](https://git.sendico.io/tech/sxchnge/issues/66),
-branch `wallet-66`, [PR #68](https://git.sendico.io/tech/sxchnge/pulls/68).
-Merge and deployment remain separate.
+Measurement: `sxchnge_currency_accounts_setup_total{outcome="ready|failed"}` and
+`sxchnge_currency_accounts_setup_duration_seconds` cover the server setup attempt.
+`ready` is emitted only after all default bindings are confirmed, including
+idempotent completion of provider wallet/route setup for newly bound ledgers.
+Each signup/resend/wallet load is a separate attempt; a retry is not a new unique
+customer conversion. The failure fraction uses all attempts as its denominator;
+the histogram measures one attempt, not time across multiple browser sessions.
+No customer, ledger, currency, balance, credentials or form input is a metric
+label. These server metrics do not measure client abandonment or prove that a
+balance card was viewed. Existing transaction journey outcomes below are reused;
+no speculative button-click events are added.
+
+Scope and rollout: [task #72](https://git.sendico.io/tech/sxchnge/issues/72), branch
+`wallet-72`, [task #72](https://git.sendico.io/tech/sxchnge/issues/72). The provider
+prerequisite and deployment order are documented in [payments](../payments.md).
+Merge and deployment remain separate. Final validation is recorded in the task
+and PR, including any transient failures and environmental blockers.
 
 ## Journey measurement plan