test(books): cover same-day reading completion

Protect equal manual start and finish dates through the client and status API.

Closes #1097

client/src/features/book/components/__tests__/DetailsTab.spec.ts

@@ -358,6 +358,54 @@ describe('DetailsTab - present state', () => {
     )
   })
 
+  it('allows the finished date to match the started date', async () => {
+    vi.mocked(api).mockImplementation(async (input, init) => {
+      if (input === '/api/v1/books/1/status' && init?.method === 'PATCH') {
+        return makeApiResponse({
+          status: 'read',
+          source: 'manual',
+          startedAt: '2026-04-10',
+          finishedAt: '2026-04-10',
+          updatedAt: '2026-04-10T00:00:00.000Z',
+        })
+      }
+      if (input === '/api/v1/collections/membership') return makeApiResponse([])
+      return makeApiResponse({}, false)
+    })
+
+    const wrapper = mount(DetailsTab, {
+      props: {
+        book: makeBook({
+          readStatus: {
+            status: 'reading',
+            source: 'manual',
+            startedAt: '2026-04-10',
+            finishedAt: null,
+            updatedAt: '2026-04-10T00:00:00.000Z',
+          },
+        }),
+      },
+      global: globalStubs,
+    })
+
+    await wrapper.find('button[title="Edit date finished"]').trigger('click')
+    await wrapper.find('input[type="date"]').setValue('2026-04-10')
+
+    const saveButton = wrapper.findAll('button').find((button) => button.text() === 'Save')
+    expect(saveButton?.exists()).toBe(true)
+    await saveButton!.trigger('click')
+    await flushPromises()
+
+    expect(wrapper.text()).not.toContain('Date Finished must be on or after Date Started')
+    expect(vi.mocked(api)).toHaveBeenCalledWith(
+      '/api/v1/books/1/status',
+      expect.objectContaining({
+        method: 'PATCH',
+        body: JSON.stringify({ finishedAt: '2026-04-10' }),
+      }),
+    )
+  })
+
   it('shows validation for finished date earlier than started date and blocks save', async () => {
     vi.mocked(api).mockImplementation(async (input) => {
       if (input === '/api/v1/collections/membership') return makeApiResponse([])

server/test/reading-attempts.e2e-spec.ts

@@ -644,6 +644,14 @@ describe('Reading attempts main-flow simulation (docker e2e)', { timeout: TIMEOU
     expect((await listAttempts(bothDates.bookId)).items).toEqual([
       expect.objectContaining({ startedOn: '2026-02-01', endedOn: '2026-02-10', outcome: 'completed', origin: 'manual' }),
     ]);
+
+    const sameDay = await createBook();
+    const sameDayResponse = await patchStatus(sameDay.bookId, { startedAt: '2026-02-15', finishedAt: '2026-02-15' });
+    expect(sameDayResponse.statusCode).toBe(200);
+    expect(sameDayResponse.json()).toMatchObject({ status: 'read', startedAt: '2026-02-15', finishedAt: '2026-02-15' });
+    expect((await listAttempts(sameDay.bookId)).items).toEqual([
+      expect.objectContaining({ startedOn: '2026-02-15', endedOn: '2026-02-15', outcome: 'completed', origin: 'manual' }),
+    ]);
   });
 
   it('27. closes active lifecycle states with a date-only finish patch', async () => {