Build exchange workspace and shared transaction services (#28)

docs/implementation.md

@@ -195,3 +195,42 @@ essential information, accessibility, and recovery. Documentation only.
 Validation: skill-creator `quick_validate.py` passed in an isolated environment
 with PyYAML (the system Python lacked it); `git diff --check` passed. No runtime
 tests were needed. The PR is not merged.
+
+## Exchange workspace — task #28
+
+- Branch `workspace-28`, stacked on `limits-22` / PR #23. Merge KYC #21 first,
+  then limits #23, then retarget this workspace contribution to main. The approved
+  plan from #24/#25 is included and updated for the user's available-only direction.
+- Implemented Accounts, Activity/detail, Limits and Settings in a responsive
+  go_router shell, with top-up, exchange and payout input/review/status flows.
+  One action group follows the selected currency; all colors use theme roles.
+  Only available balances are displayed. Status explains credit timing, outgoing
+  amount plus fee, completion and full return after failure.
+- Shared `sxchnge_wallet` service/providers own coherent demo balances, quotes,
+  idempotent submissions, reconciliation, history, account language and live
+  snapshot refresh. The limits adapter reuses the KYC DTO/mapper and refreshes
+  usage when operations change. Widgets consume provider models.
+- Language is in account settings, with failed-save feedback and retry. Public
+  auth and verified-email screens enter the workspace. KYC remains optional;
+  the demo service enforces its basic/verified outgoing caps at submission.
+- UX review: EN/RU at 320px with 1.6 text scaling; available-only presentation;
+  field preservation after errors; explicit draft discard; quote expiry;
+  loading/stale/empty states; operation outcome explanations; accessible labels,
+  semantic status announcements and focus after quote/errors. Browser walkthrough
+  verifies quote amounts and service-confirmed credit with the exchange handoff.
+  Native mobile and dedicated VoiceOver/TalkBack testing remain release QA.
+- Measurement review: typed draft/quote/submission/settlement steps with scoped
+  journey IDs, safe failure enums, simulated flag and deduplicated terminal
+  outcomes. No financial amounts, recipients or account IDs in events. Pending
+  app closure is not draft abandonment. Real PostHog delivery and cross-session
+  server outcomes remain integration work.
+- Validation passed: `make test-frontend` (115 tests), `flutter analyze` in app,
+  sxchnge_wallet, sxchnge_analytics and sxchnge_kyc; format check of all 36 changed
+  Dart files; `flutter build web`; `git diff --check`. Review fixes included
+  narrow Russian layouts, limit-provider typing, automatic pending refresh,
+  single-use quotes and ambiguous-response recovery. No security scan requested.
+- Demo limits: opening EUR 75, fixed rates/fees and three currencies, no real
+  payment methods/bank validation/storage/auth enforcement. Account preferences,
+  history and balances reset on reload. No receipt export, date pagination,
+  notification preferences or security settings beyond an honest capability note.
+  Backend adapters must supply these before production use; see the wallet README.