History Mini App

[madhead]

Finish the half-built History Mini App — a Telegram Mini App that lists a group's shared expenses with live, debounced, per-field search and infinite pagination. Launched via the group-bound, HISTORY-scoped, 30-min deep-link token minted by /history.

This is the next thing to build. The visible half is the frontend, but the bigger lift is the backend: search is currently a stub.

Backend

• Real search. Today TransactionsSearchParams has only title, and TransactionsSearchService.search() ignores it — it returns every transaction for the group. Implement actual filtering in the TransactionRepository Postgres adapter via a dynamic WHERE (all filters optional; empty = match all):
  • title — case-insensitive substring (ILIKE)
  • participant(s) — "involves member": payer OR present in recipients; multi-select, any-of
  • amount — min/max range (only meaningful together with a currency)
  • currency — exact match (from the group's used currencies)
  • date — from/to range on timestamp (stored UTC)
• Pagination — keyset/cursor, not OFFSET (degrades on deep history). ORDER BY timestamp DESC, id DESC; cursor = last-seen (timestamp, id); return a next-cursor. Page size ~30.
• API wiring. Thread query params through GET /app/api/group/transactions?title=&currency=&amountMin=&amountMax=&from=&to=&participant=&cursor= into TransactionsSearchParams. Keep the existing BigDecimal/Instant serializers.

Frontend

• Filter bar — one control per field, no Search button; search fires on edit, debounced (~300ms).
• Infinite scroll — IntersectionObserver sentinel; append pages by cursor.
• Transaction widget rework:
  • Resolve payer + recipient IDs → names via GET /app/api/group/members (fetch once, cache in memory).
  • Render payer, recipients (the .participants area is currently empty), amount, currency, title, date.
  • Replace hand-rolled Amount.formatAmount with Intl.NumberFormat (locale + currency aware).
• States — loading, empty, and error states + an ErrorBoundary (today HistoryApp does setTransactions(await res.json()) with no handling).
• Lifecycle — WebApp.ready() (dismiss the Telegram splash) and WebApp.expand() (full viewport).

Digested from #294 (Mini App findings)

• Transaction.tsx doesn't render participants — the .participants div is empty, so history cards never show who paid / who owes (needs /group/members to resolve IDs → names).
• group/members endpoint has no client caller (consumed here, for names). The frontend only calls auth/validation and group/transactions; group/members and group/currencies have no client callers.
• No loading / error / empty states, no error boundary. HistoryApp.tsx does setTransactions(await response.json()) with no error handling (failed/non-JSON response throws unhandled); no loading indicator, no empty state, no ErrorBoundary. AppWrapper shows a blank screen (null) while auth is in flight.
• Missing Mini App lifecycle calls. No WebApp.ready() (dismiss Telegram's loading placeholder) and no WebApp.expand() (full viewport). No MainButton/BackButton integration (MainButton is the idiomatic submit affordance for the future expense form).
• Amount.formatAmount hand-trims trailing zeros with string slicing and is locale-blind — prefer Intl.NumberFormat.

Open questions

• Participant filter: single "involves" selector (default) vs separate payer/recipient filters?
• Amount filter UX: force a currency when an amount range is set? (cross-currency amounts aren't comparable)
• Final page-size / debounce values
• Sort: newest-first only, or expose sort options?

Notes / technical details

• Token TTL is by design. Deep-linked apps keep the short 30-min token (indefinite tokens would be bad). Expiry surfaces as 401 + X-Auth-Error: token_expired, which the FE already maps to a "reopen" message — no refresh path for deep-linked launches. Some sort of an HTTP interceptor might be installed, so that if a Mini App makes an HTTP request with an expired token, it is cleared (like the AppWrapper does on init).
• Language mismatch (deferred). i18n currently keys off the user's Telegram language_code while the bot uses GroupConfig.language, so the app and bot can render different languages. Solvable later (we know user↔group at auth time and can return the group language). Not in scope here.