diff --git a/__tests__/hooks/use-online-status.test.ts b/__tests__/hooks/use-online-status.test.ts
new file mode 100644
index 0000000..5f0f351
--- /dev/null
+++ b/__tests__/hooks/use-online-status.test.ts
@@ -0,0 +1,59 @@
+import { describe, it, expect, afterEach } from 'vitest'
+import { renderHook, act } from '@testing-library/react'
+import { useOnlineStatus } from '@/hooks/use-online-status'
+
+function setNavigatorOnline(online: boolean) {
+  Object.defineProperty(navigator, 'onLine', { configurable: true, get: () => online })
+}
+
+describe('useOnlineStatus', () => {
+  afterEach(() => {
+    setNavigatorOnline(true)
+  })
+
+  it('defaults to online', () => {
+    const { result } = renderHook(() => useOnlineStatus())
+    expect(result.current).toBe(true)
+  })
+
+  it('syncs to navigator.onLine on mount', () => {
+    setNavigatorOnline(false)
+    const { result } = renderHook(() => useOnlineStatus())
+    expect(result.current).toBe(false)
+  })
+
+  it('becomes false when the offline event fires', () => {
+    const { result } = renderHook(() => useOnlineStatus())
+
+    act(() => {
+      window.dispatchEvent(new Event('offline'))
+    })
+
+    expect(result.current).toBe(false)
+  })
+
+  it('becomes true again when the online event fires', () => {
+    const { result } = renderHook(() => useOnlineStatus())
+
+    act(() => {
+      window.dispatchEvent(new Event('offline'))
+    })
+    expect(result.current).toBe(false)
+
+    act(() => {
+      window.dispatchEvent(new Event('online'))
+    })
+    expect(result.current).toBe(true)
+  })
+
+  it('removes its event listeners on unmount', () => {
+    const { result, unmount } = renderHook(() => useOnlineStatus())
+    unmount()
+
+    // No assertion possible on a removed listener directly, but dispatching
+    // after unmount must not throw (no dangling state updates on an
+    // unmounted component).
+    expect(() => window.dispatchEvent(new Event('offline'))).not.toThrow()
+    expect(result.current).toBe(true)
+  })
+})
diff --git a/__tests__/hooks/use-page-visibility.test.ts b/__tests__/hooks/use-page-visibility.test.ts
new file mode 100644
index 0000000..07636e7
--- /dev/null
+++ b/__tests__/hooks/use-page-visibility.test.ts
@@ -0,0 +1,81 @@
+import { describe, it, expect, vi, afterEach } from 'vitest'
+import { renderHook } from '@testing-library/react'
+import { usePageVisibility } from '@/hooks/use-page-visibility'
+
+// Issue #740 describes this hook as returning state that updates on
+// visibilitychange. The real hook (hooks/use-page-visibility.ts) returns
+// nothing — it's callback-based: it calls onVisible/onHidden depending on
+// document.hidden when the event fires. These tests cover the real shape.
+
+function setDocumentHidden(hidden: boolean) {
+  Object.defineProperty(document, 'hidden', { configurable: true, get: () => hidden })
+}
+
+function fireVisibilityChange() {
+  document.dispatchEvent(new Event('visibilitychange'))
+}
+
+describe('usePageVisibility', () => {
+  afterEach(() => {
+    setDocumentHidden(false)
+  })
+
+  it('calls onHidden when the document becomes hidden', () => {
+    const onVisible = vi.fn()
+    const onHidden = vi.fn()
+    renderHook(() => usePageVisibility({ onVisible, onHidden }))
+
+    setDocumentHidden(true)
+    fireVisibilityChange()
+
+    expect(onHidden).toHaveBeenCalledTimes(1)
+    expect(onVisible).not.toHaveBeenCalled()
+  })
+
+  it('calls onVisible when the document becomes visible again', () => {
+    const onVisible = vi.fn()
+    const onHidden = vi.fn()
+    renderHook(() => usePageVisibility({ onVisible, onHidden }))
+
+    setDocumentHidden(true)
+    fireVisibilityChange()
+    setDocumentHidden(false)
+    fireVisibilityChange()
+
+    expect(onHidden).toHaveBeenCalledTimes(1)
+    expect(onVisible).toHaveBeenCalledTimes(1)
+  })
+
+  it('does not throw when a callback is omitted', () => {
+    renderHook(() => usePageVisibility({ onHidden: vi.fn() }))
+    setDocumentHidden(false)
+    expect(() => fireVisibilityChange()).not.toThrow()
+  })
+
+  it('always calls the latest callback identity, even without re-registering the listener', () => {
+    const onHiddenFirst = vi.fn()
+    const onHiddenSecond = vi.fn()
+    const { rerender } = renderHook(({ onHidden }) => usePageVisibility({ onHidden }), {
+      initialProps: { onHidden: onHiddenFirst },
+    })
+
+    rerender({ onHidden: onHiddenSecond })
+
+    setDocumentHidden(true)
+    fireVisibilityChange()
+
+    expect(onHiddenFirst).not.toHaveBeenCalled()
+    expect(onHiddenSecond).toHaveBeenCalledTimes(1)
+  })
+
+  it('removes the listener on unmount', () => {
+    const onHidden = vi.fn()
+    const { unmount } = renderHook(() => usePageVisibility({ onHidden }))
+
+    unmount()
+    setDocumentHidden(true)
+    fireVisibilityChange()
+
+    expect(onHidden).not.toHaveBeenCalled()
+  })
+})
diff --git a/__tests__/hooks/use-streams-view-preference.test.ts b/__tests__/hooks/use-streams-view-preference.test.ts
new file mode 100644
index 0000000..5b151d8
--- /dev/null
+++ b/__tests__/hooks/use-streams-view-preference.test.ts
@@ -0,0 +1,39 @@
+import { describe, it, expect, beforeEach } from 'vitest'
+import { renderHook, act } from '@testing-library/react'
+import { useStreamsViewPreference } from '@/hooks/use-streams-view-preference'
+
+const KEY = 'flowstar:streams-view'
+
+describe('useStreamsViewPreference', () => {
+  beforeEach(() => {
+    localStorage.clear()
+  })
+
+  it('defaults to "list" when nothing is stored', () => {
+    const { result } = renderHook(() => useStreamsViewPreference())
+    expect(result.current.view).toBe('list')
+  })
+
+  it('reads a previously stored preference', () => {
+    localStorage.setItem(KEY, 'compact')
+    const { result } = renderHook(() => useStreamsViewPreference())
+    expect(result.current.view).toBe('compact')
+  })
+
+  it('ignores an invalid stored value and falls back to the default', () => {
+    localStorage.setItem(KEY, 'not-a-real-view')
+    const { result } = renderHook(() => useStreamsViewPreference())
+    expect(result.current.view).toBe('list')
+  })
+
+  it('setView updates state and persists to localStorage', () => {
+    const { result } = renderHook(() => useStreamsViewPreference())
+
+    act(() => {
+      result.current.setView('timeline')
+    })
+
+    expect(result.current.view).toBe('timeline')
+    expect(localStorage.getItem(KEY)).toBe('timeline')
+  })
+})
diff --git a/__tests__/hooks/use-undo-cancel.test.ts b/__tests__/hooks/use-undo-cancel.test.ts
new file mode 100644
index 0000000..048baa7
--- /dev/null
+++ b/__tests__/hooks/use-undo-cancel.test.ts
@@ -0,0 +1,136 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest'
+import { renderHook, act } from '@testing-library/react'
+
+vi.mock('@/hooks/use-contract', () => ({
+  useContract: vi.fn(),
+}))
+
+vi.mock('sonner', () => {
+  const toast = vi.fn() as unknown as { (...args: unknown[]): void; dismiss: ReturnType<typeof vi.fn>; info: ReturnType<typeof vi.fn> }
+  toast.dismiss = vi.fn()
+  toast.info = vi.fn()
+  return { toast }
+})
+
+import { useContract } from '@/hooks/use-contract'
+import { toast } from 'sonner'
+import { useUndoableCancel, useIsStreamCancelling, CANCEL_UNDO_DELAY_MS } from '@/hooks/use-undo-cancel'
+
+const cancelMock = vi.fn()
+
+describe('useUndoableCancel / useIsStreamCancelling', () => {
+  beforeEach(() => {
+    vi.useFakeTimers()
+    cancelMock.mockReset().mockResolvedValue(undefined)
+    vi.mocked(useContract).mockReturnValue({ cancel: cancelMock } as unknown as ReturnType<typeof useContract>)
+    vi.mocked(toast).mockClear()
+    vi.mocked(toast.dismiss).mockClear()
+    vi.mocked(toast.info).mockClear()
+  })
+
+  afterEach(() => {
+    vi.useRealTimers()
+  })
+
+  it('marks the stream as cancelling immediately when scheduled', () => {
+    const { result: cancelHook } = renderHook(() => useUndoableCancel())
+    const { result: isCancelling } = renderHook(() => useIsStreamCancelling('stream-1'))
+
+    expect(isCancelling.current).toBe(false)
+
+    act(() => {
+      cancelHook.current.scheduleCancel('stream-1')
+    })
+
+    expect(isCancelling.current).toBe(true)
+    expect(cancelMock).not.toHaveBeenCalled()
+  })
+
+  it('submits the cancel transaction once the undo delay elapses (cancel-on-timeout)', async () => {
+    const { result: cancelHook } = renderHook(() => useUndoableCancel())
+    const { result: isCancelling } = renderHook(() => useIsStreamCancelling('stream-1'))
+
+    act(() => {
+      cancelHook.current.scheduleCancel('stream-1')
+    })
+    expect(isCancelling.current).toBe(true)
+
+    await act(async () => {
+      await vi.advanceTimersByTimeAsync(CANCEL_UNDO_DELAY_MS)
+    })
+
+    expect(cancelMock).toHaveBeenCalledWith('stream-1')
+    expect(isCancelling.current).toBe(false)
+    expect(toast.dismiss).toHaveBeenCalledWith('cancel-undo-stream-1')
+  })
+
+  it('aborting before the delay elapses cancels the countdown and never submits the transaction (undo-before-timeout)', async () => {
+    const { result: cancelHook } = renderHook(() => useUndoableCancel())
+    const { result: isCancelling } = renderHook(() => useIsStreamCancelling('stream-1'))
+
+    act(() => {
+      cancelHook.current.scheduleCancel('stream-1')
+    })
+
+    act(() => {
+      vi.advanceTimersByTime(CANCEL_UNDO_DELAY_MS / 2)
+    })
+    expect(isCancelling.current).toBe(true)
+
+    act(() => {
+      const aborted = cancelHook.current.abortCancel('stream-1')
+      expect(aborted).toBe(true)
+    })
+
+    expect(isCancelling.current).toBe(false)
+
+    // Advancing past the original delay must not retroactively submit the
+    // cancel — the timers backing it were cleared by abortCancel.
+    await act(async () => {
+      await vi.advanceTimersByTimeAsync(CANCEL_UNDO_DELAY_MS)
+    })
+    expect(cancelMock).not.toHaveBeenCalled()
+  })
+
+  it('abortCancel returns false when there is nothing pending for that stream', () => {
+    const { result: cancelHook } = renderHook(() => useUndoableCancel())
+
+    act(() => {
+      const aborted = cancelHook.current.abortCancel('never-scheduled')
+      expect(aborted).toBe(false)
+    })
+  })
+
+  it('useIsStreamCancelling reacts to a cancellation scheduled by a different hook instance', () => {
+    const { result: cancelHookA } = renderHook(() => useUndoableCancel())
+    const { result: isCancellingB } = renderHook(() => useIsStreamCancelling('shared-stream'))
+
+    expect(isCancellingB.current).toBe(false)
+
+    act(() => {
+      cancelHookA.current.scheduleCancel('shared-stream')
+    })
+
+    // A separate hook instance subscribed to the same stream id observes the
+    // change via the shared pub/sub, without any prop-drilling between them.
+    expect(isCancellingB.current).toBe(true)
+  })
+
+  it('unmounting the scheduling component aborts any in-flight countdown', async () => {
+    const { result: cancelHook, unmount } = renderHook(() => useUndoableCancel())
+    const { result: isCancelling } = renderHook(() => useIsStreamCancelling('stream-1'))
+
+    act(() => {
+      cancelHook.current.scheduleCancel('stream-1')
+    })
+    expect(isCancelling.current).toBe(true)
+
+    unmount()
+    expect(isCancelling.current).toBe(false)
+
+    await act(async () => {
+      await vi.advanceTimersByTimeAsync(CANCEL_UNDO_DELAY_MS)
+    })
+    expect(cancelMock).not.toHaveBeenCalled()
+  })
+})