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docs: add ADR-004 TanStack Query migration
- Document migration rationale and trade-offs - Add TanStack Query patterns to CLAUDE.md - Include testing patterns and key benefits Co-Authored-By: Claude
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‎CLAUDE.md‎

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- Fetches in batches via `rvlimit=max` with continuation tokens (`rvcontinue`)
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- Client-side dump processing was considered and rejected due to prohibitive download times (ADR-003)
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## TanStack Query Integration (ADR-004)
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The application uses TanStack Query for page ID fetching with the following patterns:
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### Query Configuration
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- **QueryClientProvider** in @src/App.tsx with:
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- 1-hour `staleTime` for automatic caching (page IDs are immutable)
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- Single retry on failure
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- ReactQueryDevtools in development mode
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### Page ID Fetching Pattern
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@src/components/PageTitleInput.tsx:
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- Uses TanStack Pacer's `useDebouncedValue` (300ms) for input debouncing
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- Always renders QueryErrorResetBoundary > ErrorBoundary > Suspense > PageIdFetcher (no conditional branching)
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- Uses `react-error-boundary` package with `resetKeys={[debouncedTitle]}` for automatic error recovery on title change
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- Discriminates 404 errors (page not found) from other errors using `isNotFoundError()` helper
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- Shows retry button with inline link styling for non-404 errors
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- Renders hidden `<input name="pageId">` in error fallback to prevent form submission
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@src/components/PageIdFetcher.tsx:
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- Uses `useSuspenseQuery` with query key `['pageId', wikiUrl.href, pageTitle]`
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- Handles empty title inside `queryFn`: returns `null` for empty title (quick-resolving, no Suspense flash)
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- Passes `AbortSignal` from query to `fetchPageId` for request cancellation
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- Throws errors for ErrorBoundary to catch (no inline error handling)
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### Key Benefits
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- **Request cancellation**: In-flight requests automatically aborted on input change
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- **Automatic caching**: Same page title returns cached result (1h staleTime, page IDs are immutable)
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- **Deduplication**: Multiple components requesting same data share one request
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- **Promise stability**: Query cache handles promise reference stability
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### Testing Pattern
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All components using queries must be wrapped in `QueryClientProvider`:
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```tsx
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const renderWithQuery = (component: React.ReactElement) => {
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return render(
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<QueryClientProvider client={queryClient}>
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{component}
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</QueryClientProvider>
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);
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};
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```
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## Testing Requirements (TDD Workflow)
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Uses **Vitest** with **in-source testing** pattern. All source files MUST include tests:
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- **ADR-001**: Removed revision sampling in favor of linear streaming search for code simplicity
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- **ADR-002**: Enabled client-side caching with `maxage` parameter (60s for recent, 600s for historical)
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- **ADR-003**: Rejected client-side dump processing due to prohibitive download speeds
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- **ADR-004**: Migrated to TanStack Query for page ID fetching (replaced useMemo + use() pattern)
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## Deployment
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‎docs/adr/004-tanstack-query-migration.md‎

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# ADR-004: Migration to TanStack Query
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## Status
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Accepted
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## Context
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The application initially used a `useMemo` + `use()` hook pattern for fetching page IDs in `PageTitleInput.tsx`. While functional, this pattern has several issues:
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1. **Anti-pattern**: React 19 documentation explicitly warns against creating promises in Client Components
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2. **No request cancellation**: In-flight requests cannot be aborted when dependencies change
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3. **Manual memoization**: Requires careful dependency array management
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4. **Promise recreation**: Every dependency change creates a new promise
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5. **No caching**: Repeated searches for the same title refetch unnecessarily
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6. **Future risk**: React may tighten enforcement of this pattern in future versions
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## Decision
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Migrate from the `useMemo` + `use()` pattern to TanStack Query with the following architecture:
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- Use `useSuspenseQuery` for data fetching (idiomatic React 19 pattern)
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- Use TanStack Pacer's `useDebouncedValue` for input debouncing (300ms)
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- Implement component composition pattern for conditional rendering (since `useSuspenseQuery` doesn't support `enabled` option)
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- Add `AbortSignal` support to `fetchPageId` for proper request cancellation
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- Set 1-hour `staleTime` for automatic caching (page IDs are immutable)
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## Consequences
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### Positive
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- **Idiomatic React 19**: Follows official React guidance for data fetching
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- **Automatic caching**: Same title returns cached response (1h staleTime, page IDs are immutable)
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- **Request cancellation**: AbortSignal propagated to fetch, cancels in-flight requests
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- **Promise stability**: Global query cache handles stability automatically
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- **Deduplication**: Multiple components requesting same data share one request
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- **DevTools**: TanStack Query DevTools available for debugging cache/queries
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- **Background refetch**: Configurable stale-while-revalidate behavior
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### Negative
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- **Bundle size increase**: ~13.91 KB gzipped (70.74 KB → 84.65 KB)
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- **Additional dependency**: Requires TanStack Query and Pacer packages
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- **Increased complexity**: Requires QueryProvider setup and understanding query concepts
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- **Learning curve**: Team needs to understand TanStack Query patterns
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### Implementation Details
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#### Component Composition Pattern
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`PageTitleInput.tsx` always renders the same structure without conditional branching:
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```tsx
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<QueryErrorResetBoundary>
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{({ reset }) => (
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<ErrorBoundary
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resetKeys={[debouncedTitle]}
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onReset={reset}
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fallbackRender={({ error, resetErrorBoundary }) => (
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// Error UI with retry button and hidden pageId input
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)}
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>
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<Suspense fallback={<LoadingIndicator />}>
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<PageIdFetcher wikiUrl={wikiUrl} pageTitle={debouncedTitle} />
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</Suspense>
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</ErrorBoundary>
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)}
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</QueryErrorResetBoundary>
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```
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The component uses `react-error-boundary` package for enhanced error handling:
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- **`QueryErrorResetBoundary`**: Coordinates error boundary resets with TanStack Query cache
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- **`resetKeys={[debouncedTitle]}`**: Automatically resets error boundary when title changes
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- **`onReset={reset}`**: Synchronizes with TanStack Query's error state
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- **404 discrimination**: Uses `isNotFoundError()` helper to distinguish 404s from other errors
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- **Retry button**: Displayed only for non-404 errors with inline link styling
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- **Hidden input**: Renders `<input name="pageId">` in error fallback to prevent form submission with invalid page ID
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`PageIdFetcher.tsx` handles empty title in `queryFn` to avoid Rules of Hooks violations:
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```tsx
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const { data: pageId } = useSuspenseQuery({
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queryKey: ['pageId', wikiUrl.href, pageTitle],
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queryFn: ({ signal }) => pageTitle ? fetchPageId(wikiUrl, pageTitle, signal) : null,
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});
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```
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When `pageTitle` is empty, the `queryFn` returns `null` immediately (no network request, no Suspense flash).
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#### AbortSignal Propagation
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```tsx
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export async function fetchPageId(
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baseUrl: URL,
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pageTitle: string,
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signal: AbortSignal | null = null,
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): Promise<number> {
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const response = await fetch(url, { signal });
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// ...
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}
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```
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#### Query Configuration
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```tsx
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const queryClient = new QueryClient({
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defaultOptions: {
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queries: {
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staleTime: 1 * 60 * 60 * 1000, // 1 hour (page IDs are immutable)
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retry: 1,
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},
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},
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});
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```
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## References
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- [React 19 Documentation on use() hook](https://react.dev/reference/react/use)
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- [TanStack Query Documentation](https://tanstack.com/query/latest)
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- [TanStack Pacer Documentation](https://tanstack.com/pacer/latest)
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- [react-error-boundary Documentation](https://github.com/bvaughn/react-error-boundary)

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