diff --git a/apps/worker/src/screens/Stopwatch.test.tsx b/apps/worker/src/screens/Stopwatch.test.tsx
index d3e04cd..c861307 100644
--- a/apps/worker/src/screens/Stopwatch.test.tsx
+++ b/apps/worker/src/screens/Stopwatch.test.tsx
@@ -1,4 +1,4 @@
-import { render, screen, waitFor } from '@testing-library/react';
+import { act, fireEvent, render, screen, waitFor } from '@testing-library/react';
 import userEvent from '@testing-library/user-event';
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
 import { QueryClient, QueryClientProvider } from '@tanstack/react-query';
@@ -296,4 +296,197 @@ describe('Stopwatch', () => {
     );
     expect(screen.queryByRole('button', { name: 'Stop & Opslaan' })).not.toBeInTheDocument();
   });
+
+  it('starts by tapping the display when idle and a handling is chosen', async () => {
+    const user = userEvent.setup();
+    renderStopwatch();
+
+    await user.selectOptions(screen.getByLabelText('Type handeling'), 'Frezen');
+    await user.click(screen.getByRole('button', { name: 'Stopwatch' }));
+
+    expect(startMutate).toHaveBeenCalledTimes(1);
+  });
+
+  it('does not start on a display tap when idle with no handling chosen', async () => {
+    const user = userEvent.setup();
+    renderStopwatch();
+
+    await user.click(screen.getByRole('button', { name: 'Stopwatch' }));
+
+    expect(startMutate).not.toHaveBeenCalled();
+  });
+
+  it('decrements the pair count and disables the minus button at the floor of 1', async () => {
+    const user = userEvent.setup();
+    renderStopwatch();
+
+    const input = screen.getByLabelText('Aantal zolen');
+    expect(input).toHaveValue('2');
+
+    await user.click(screen.getByRole('button', { name: 'Minder zolen' }));
+    expect(input).toHaveValue('1');
+    expect(screen.getByRole('button', { name: 'Minder zolen' })).toBeDisabled();
+  });
+
+  it('accepts a free-typed pair count and ignores a non-positive value', async () => {
+    const user = userEvent.setup();
+    renderStopwatch();
+
+    const input = screen.getByLabelText('Aantal zolen');
+    await user.clear(input);
+    await user.type(input, '7');
+    expect(input).toHaveValue('7');
+
+    // A non-positive entry is mirrored in the field but is not adopted as the count.
+    await user.clear(input);
+    await user.type(input, '0');
+    expect(input).toHaveValue('0');
+
+    // Starting uses the last valid count (7), proving the '0' was ignored.
+    await user.selectOptions(screen.getByLabelText('Type handeling'), 'Frezen');
+    await user.click(screen.getByRole('button', { name: 'Start Stopwatch' }));
+    expect(startMutate.mock.calls[0][0]).toMatchObject({ pair_count: 7 });
+  });
+
+  it('clears the chosen handling when the empty option is reselected', async () => {
+    const user = userEvent.setup();
+    renderStopwatch();
+
+    const select = screen.getByLabelText('Type handeling');
+    await user.selectOptions(select, 'Frezen');
+    expect(screen.getByRole('button', { name: 'Start Stopwatch' })).toBeEnabled();
+
+    await user.selectOptions(select, '');
+    expect(screen.getByRole('button', { name: 'Start Stopwatch' })).toBeDisabled();
+  });
+
+  it('resets to idle when stop succeeds', async () => {
+    const user = userEvent.setup();
+    stopMutate.mockImplementation((_id: number, opts?: { onSuccess?: () => void }) => {
+      opts?.onSuccess?.();
+    });
+    mockedUseActiveSessions.mockReturnValue(
+      query<ReturnType<typeof useActiveSessions>>([activeSession()]),
+    );
+    renderStopwatch();
+
+    await user.click(await screen.findByRole('button', { name: 'Stop & Opslaan' }));
+
+    expect(await screen.findByRole('button', { name: 'Start Stopwatch' })).toBeInTheDocument();
+    expect(screen.queryByRole('button', { name: 'Stop & Opslaan' })).not.toBeInTheDocument();
+  });
+
+  it('resets to idle when discard is confirmed and succeeds', async () => {
+    const user = userEvent.setup();
+    discardMutate.mockImplementation((_id: number, opts?: { onSuccess?: () => void }) => {
+      opts?.onSuccess?.();
+    });
+    mockedUseActiveSessions.mockReturnValue(
+      query<ReturnType<typeof useActiveSessions>>([activeSession()]),
+    );
+    renderStopwatch();
+
+    await user.click(await screen.findByRole('button', { name: 'Annuleren' }));
+    await user.click(screen.getByRole('button', { name: 'Nogmaals tikken ter bevestiging' }));
+
+    expect(discardMutate).toHaveBeenCalledTimes(1);
+    expect(await screen.findByRole('button', { name: 'Start Stopwatch' })).toBeInTheDocument();
+  });
+
+  it('disarms discard after the confirm window expires', () => {
+    // Fake timers + fireEvent (userEvent's internal delays fight the 1s display tick).
+    vi.useFakeTimers();
+    mockedUseActiveSessions.mockReturnValue(
+      query<ReturnType<typeof useActiveSessions>>([activeSession()]),
+    );
+    renderStopwatch();
+
+    fireEvent.click(screen.getByRole('button', { name: 'Annuleren' }));
+    expect(
+      screen.getByRole('button', { name: 'Nogmaals tikken ter bevestiging' }),
+    ).toBeInTheDocument();
+
+    // The 3s arm window lapses without a second tap → discard disarms back to 'Annuleren'.
+    act(() => {
+      vi.advanceTimersByTime(3000);
+    });
+    expect(screen.getByRole('button', { name: 'Annuleren' })).toBeInTheDocument();
+  });
+
+  it('clears a pending discard timer when the session is reconciled away', async () => {
+    const user = userEvent.setup();
+    mockedUseActiveSessions.mockReturnValue(
+      query<ReturnType<typeof useActiveSessions>>([activeSession()]),
+    );
+    const { rerender } = renderStopwatch();
+
+    // Arm discard so a pending timer exists when the reconcile reset fires.
+    await user.click(await screen.findByRole('button', { name: 'Annuleren' }));
+    await screen.findByRole('button', { name: 'Nogmaals tikken ter bevestiging' });
+
+    // Admin stops the session: the poll no longer lists it → resetTimer clears the armed timer.
+    mockedUseActiveSessions.mockReturnValue(query<ReturnType<typeof useActiveSessions>>([]));
+    const queryClient = new QueryClient({ defaultOptions: { queries: { retry: false } } });
+    rerender(
+      <QueryClientProvider client={queryClient}>
+        <Stopwatch />
+      </QueryClientProvider>,
+    );
+
+    expect(
+      await screen.findByText('Deze sessie is door de beheerder gestopt.'),
+    ).toBeInTheDocument();
+    expect(screen.getByRole('button', { name: 'Start Stopwatch' })).toBeInTheDocument();
+  });
+
+  it('clears a pending discard timer on unmount', async () => {
+    const user = userEvent.setup();
+    const clearSpy = vi.spyOn(globalThis, 'clearTimeout');
+    mockedUseActiveSessions.mockReturnValue(
+      query<ReturnType<typeof useActiveSessions>>([activeSession()]),
+    );
+    const { unmount } = renderStopwatch();
+
+    await user.click(await screen.findByRole('button', { name: 'Annuleren' }));
+    clearSpy.mockClear();
+    unmount();
+
+    expect(clearSpy).toHaveBeenCalled();
+  });
+
+  it('lifecycle: running locally, then a poll without the session resets it and shows the admin-stopped notice', async () => {
+    const user = userEvent.setup();
+    const local = activeSession({ id: 42 });
+    startMutate.mockImplementation(
+      (_input: unknown, opts?: { onSuccess?: (s: WorkSession) => void }) => {
+        opts?.onSuccess?.(local);
+      },
+    );
+    // Idle to begin with (no server-active session to adopt).
+    mockedUseActiveSessions.mockReturnValue(query<ReturnType<typeof useActiveSessions>>([]));
+    const { rerender } = renderStopwatch();
+
+    // Start locally → the screen enters the running state from the start mutation's onSuccess.
+    await user.selectOptions(screen.getByLabelText('Type handeling'), 'Frezen');
+    await user.click(screen.getByRole('button', { name: 'Start Stopwatch' }));
+    await screen.findByRole('button', { name: 'Stop & Opslaan' });
+
+    // The active-sessions poll now returns a list WITHOUT our session (only another worker's).
+    mockedUseActiveSessions.mockReturnValue(
+      query<ReturnType<typeof useActiveSessions>>([activeSession({ id: 77, user_id: 'other' })]),
+    );
+    const queryClient = new QueryClient({ defaultOptions: { queries: { retry: false } } });
+    rerender(
+      <QueryClientProvider client={queryClient}>
+        <Stopwatch />
+      </QueryClientProvider>,
+    );
+
+    // The timer resets to idle and the admin-stopped notice shows.
+    expect(
+      await screen.findByText('Deze sessie is door de beheerder gestopt.'),
+    ).toBeInTheDocument();
+    expect(screen.getByRole('button', { name: 'Start Stopwatch' })).toBeInTheDocument();
+    expect(screen.queryByRole('button', { name: 'Stop & Opslaan' })).not.toBeInTheDocument();
+  });
 });
diff --git a/apps/worker/src/screens/Stopwatch.tsx b/apps/worker/src/screens/Stopwatch.tsx
index 98fcd66..aa652bf 100644
--- a/apps/worker/src/screens/Stopwatch.tsx
+++ b/apps/worker/src/screens/Stopwatch.tsx
@@ -75,6 +75,7 @@ export default function Stopwatch() {
     // Restore pause state from the server (source of truth).
     const pausedAtMs = session.paused_at ? new Date(session.paused_at).getTime() : null;
     setIsPaused(pausedAtMs !== null);
+    /* c8 ignore next -- paused_seconds is z.number().int() (never null); ?? 0 is a defensive coalesce */
     setPausedMs((session.paused_seconds ?? 0) * 1000);
     setPauseStartedMs(pausedAtMs);
     // eslint-disable-next-line react-hooks/exhaustive-deps
@@ -102,6 +103,7 @@ export default function Stopwatch() {
   const elapsed = startMs !== null ? elapsedSeconds(startMs, effectiveNow, pausedMs) : 0;
 
   function handleSelectZool(type: InsoleType) {
+    /* c8 ignore next -- unreachable: the zool buttons are disabled while running */
     if (isRunning) return;
     setInsoleType(type);
     setActiveActivityId(null); // changing the zool clears the chosen handling
@@ -120,6 +122,7 @@ export default function Stopwatch() {
   }
 
   function handleStart() {
+    /* c8 ignore next -- unreachable: both callers gate on canStart; guard also narrows the type */
     if (!canStart || activeActivityId === null) return;
     setStoppedByAdmin(false); // clear any prior admin-stopped notice
     startSession.mutate(
@@ -177,6 +180,7 @@ export default function Stopwatch() {
   }
 
   function handleStop() {
+    /* c8 ignore next -- unreachable: the Stop button only renders while running (sessionId set) */
     if (sessionId === null) return;
     const id = sessionId;
     stopSession.mutate(id, { onSuccess: () => resetTimer(), onError: resetIfConflict });
@@ -184,6 +188,7 @@ export default function Stopwatch() {
   }
 
   function handleDiscard() {
+    /* c8 ignore next -- unreachable: the Annuleren button only renders while running (sessionId set) */
     if (sessionId === null) return;
     if (!discardPending) {
       setDiscardPending(true);
diff --git a/docs/reference/domain-test-checklist.md b/docs/reference/domain-test-checklist.md
index 968ae71..2dd355a 100644
--- a/docs/reference/domain-test-checklist.md
+++ b/docs/reference/domain-test-checklist.md
@@ -558,3 +558,43 @@ Guaranteed behaviors:
 - Lifecycle (`src/screens/Activities.test.tsx`): create a handeling → edit its insole types down to a
   single type → reorder it above another → delete it, with each step reflected in the refetched list;
   the Sidebar test (`src/components/Sidebar.test.tsx`) covers navigation switching screens.
+
+## Stopwatch + reconcile — worker client
+
+Src covered (worker `apps/worker`): `src/screens/Stopwatch.tsx` and `src/lib/stopwatch.ts` — both at
+100% stmts/branch/funcs/lines. Five `c8 ignore`s with reasons in `Stopwatch.tsx`: the
+`paused_seconds ?? 0` coalesce in the reconcile adopt (the contract types `paused_seconds` as
+`z.number().int()`, never null) and the four early-return guards in `handleSelectZool`, `handleStart`,
+`handleStop`, and `handleDiscard` — each unreachable because the button that triggers it is
+disabled or not rendered in exactly that state (and the `handleStart` guard also narrows the type).
+
+Guaranteed behaviors:
+
+- `formatTime` renders zero-padded `HH:MM:SS`, floors a negative total at `00:00:00`, and lets hours
+  exceed two digits; `elapsedSeconds` returns `(now − start − paused)` floored at 0 (paused time
+  excluded).
+- The three sections (`Type zool` / `Type handeling` / `Aantal zolen`) and the Dutch Start button
+  render; the zool segmented control offers `Kurk` / `Berk` / `3D` with `Kurk` selected by default.
+- Choosing a zooltype filters the handeling `<select>` to activities whose `insole_types` include that
+  type and clears any previously chosen handeling; picking the empty option (`Kies een handeling...`)
+  also clears the chosen handeling.
+- Start is disabled until a handeling is chosen; starting fires `useStartSession` with
+  `{ activity_id, insole_type, pair_count }` from the current selection.
+- Pair count: the stepper `+`/`−` buttons adjust the count with a floor of 1 (the `−` button is
+  disabled at 1); the free-typed field mirrors the raw text but only adopts a parsed value greater
+  than 0 (a non-positive or non-numeric entry keeps the last valid count).
+- The stopwatch display is tappable: while idle with a handeling chosen it starts the session (idle
+  tap with no handeling is a no-op); while running it pauses via `usePauseSession`; while paused it
+  resumes via `useResumeSession` (folding the just-finished pause span into the local accumulator).
+- On a successful start the screen adopts the returned session's running state (id, start time, cleared
+  pause); a paused server session is recovered into the paused UI (`Gepauzeerd — tik om te hervatten`).
+- Stop (`Stop & Opslaan`) and discard both reset the timer to idle on success; a `409` (already closed
+  server-side) on either resets locally instead of leaving the timer stuck.
+- Discard is a double-tap: the first `Annuleren` tap arms it (`Nogmaals tikken ter bevestiging`) and the
+  second confirms and fires `useDiscardSession`; the arm window lapses after 3s back to `Annuleren`, and
+  a pending arm timer is cleared both on reconcile-reset and on unmount.
+- Reconcile against the active-sessions poll: while idle with a server-active session, the screen adopts
+  it (phone-died / resume-elsewhere); the running-vs-server check keys on session id.
+- Lifecycle (`src/screens/Stopwatch.test.tsx`): running locally after a successful start, when the
+  active-sessions poll returns a list **without** the local session (only another worker's), the timer
+  resets to idle and the `Deze sessie is door de beheerder gestopt.` notice shows.