fix: dispatch ADD_START, correlate preview/lookup responses with the current attempt

web/test/scanPage.test.tsx

@@ -3,7 +3,7 @@ import { render, screen, waitFor } from '@testing-library/react'
 import userEvent from '@testing-library/user-event'
 import { MemoryRouter } from 'react-router-dom'
 import ScanPage from '../src/pages/ScanPage.js'
-import type { Candidate, ReleasePreview } from '../src/types.js'
+import type { Candidate, Item, ReleasePreview } from '../src/types.js'
 
 vi.mock('../src/components/Scanner.js', () => ({
   default: ({ onDetect }: { onDetect: (code: string) => void }) => (
@@ -48,6 +48,25 @@ const preview: ReleasePreview = {
 }
 
 // The api module is mocked directly, so mocks resolve with parsed bodies.
+const addedItem: Item = {
+  id: 1,
+  discogsReleaseId: 1001,
+  title: 'Motion',
+  artist: 'The Cinematic Orchestra',
+  year: 1999,
+  formats: ['CD'],
+  genres: [],
+  labels: ['Ninja Tune'],
+  tracklist: [],
+  catno: 'ZENCD012',
+  country: 'UK',
+  artworkUrl: null,
+  barcodes: ['5021592210629'],
+  dateAdded: '2026-08-29',
+  ripOverride: null,
+  ripStatus: 'not_ripped',
+}
+
 function jsonOk(body: unknown) {
   return Promise.resolve(body)
 }
@@ -70,26 +89,7 @@ describe('ScanPage flow', () => {
   it('scan → candidates → confirm → added', async () => {
     vi.mocked(api.lookupBarcode).mockResolvedValue(jsonOk({ candidates: [candidate] }) as never)
     vi.mocked(api.getReleasePreview).mockResolvedValue(jsonOk(preview) as never)
-    vi.mocked(api.addToCollection).mockResolvedValue(
-      jsonOk({
-        id: 1,
-        discogsReleaseId: 1001,
-        title: 'Motion',
-        artist: 'The Cinematic Orchestra',
-        year: 1999,
-        formats: ['CD'],
-        genres: [],
-        labels: ['Ninja Tune'],
-        tracklist: [],
-        catno: 'ZENCD012',
-        country: 'UK',
-        artworkUrl: null,
-        barcodes: ['5021592210629'],
-        dateAdded: '2026-08-29',
-        ripOverride: null,
-        ripStatus: 'not_ripped',
-      }) as never
-    )
+    vi.mocked(api.addToCollection).mockResolvedValue(jsonOk(addedItem) as never)
 
     renderScan()
     await userEvent.click(screen.getByRole('button', { name: 'fake-scan' }))
@@ -158,4 +158,23 @@ describe('ScanPage flow', () => {
     await waitFor(() => expect(screen.getByText(/discogs token/i)).toBeTruthy())
     expect(screen.getByRole('link', { name: /settings/i }).getAttribute('href')).toBe('/settings')
   })
+
+  it('does not add twice when the button is clicked rapidly', async () => {
+    let resolveAdd: (v: unknown) => void = () => {}
+    vi.mocked(api.lookupBarcode).mockResolvedValue(jsonOk({ candidates: [candidate] }) as never)
+    vi.mocked(api.getReleasePreview).mockResolvedValue(jsonOk(preview) as never)
+    vi.mocked(api.addToCollection).mockImplementation(
+      () => new Promise((resolve) => { resolveAdd = resolve }) as never
+    )
+    renderScan()
+    await userEvent.click(screen.getByRole('button', { name: 'fake-scan' }))
+    await userEvent.click(await screen.findByRole('button', { name: /motion/i }))
+    const addBtn = await screen.findByRole('button', { name: /add to collection/i })
+    await userEvent.click(addBtn)
+    // adding=true → button is disabled ('Adding…'); a second rapid click must not re-fire the request
+    await userEvent.click(addBtn).catch(() => {})
+    resolveAdd(addedItem)
+    await waitFor(() => expect(screen.getByText(/added to collection/i)).toBeTruthy())
+    expect(api.addToCollection).toHaveBeenCalledTimes(1)
+  })
 })