diff --git a/apps/api/src/routes/sessions.ts b/apps/api/src/routes/sessions.ts
index 4b2fa77..6b5296f 100644
--- a/apps/api/src/routes/sessions.ts
+++ b/apps/api/src/routes/sessions.ts
@@ -136,6 +136,7 @@ sessionsRoutes.post('/api/sessions/:id/resume', async (c) => {
   if (!row.pausedAt) return c.json({ error: 'Not paused' }, 409);
 
   const pausedSeconds =
+    /* c8 ignore next -- pausedSeconds is NOT NULL (default 0) in schema; ?? 0 is a defensive guard */
     (row.pausedSeconds ?? 0) + Math.round((Date.now() - new Date(row.pausedAt).getTime()) / 1000);
 
   const [updated] = await db
@@ -164,6 +165,7 @@ sessionsRoutes.post('/api/sessions/:id/stop', async (c) => {
   const extraPaused = row.pausedAt
     ? Math.round((now - new Date(row.pausedAt).getTime()) / 1000)
     : 0;
+  /* c8 ignore next -- pausedSeconds is NOT NULL (default 0) in schema; ?? 0 is a defensive guard */
   const pausedSeconds = (row.pausedSeconds ?? 0) + extraPaused;
   const endTime = new Date(now);
   const wall = Math.round((now - new Date(row.startTime).getTime()) / 1000);
diff --git a/apps/api/test/integration/worker-session-lifecycle.test.ts b/apps/api/test/integration/worker-session-lifecycle.test.ts
new file mode 100644
index 0000000..028b345
--- /dev/null
+++ b/apps/api/test/integration/worker-session-lifecycle.test.ts
@@ -0,0 +1,69 @@
+import { describe, it, expect, beforeEach } from 'vitest';
+import { eq } from 'drizzle-orm';
+import { createApp } from '../../src/app';
+import { db } from '../../src/db/client';
+import { workSessions } from '../../src/db/schema';
+import { authToken, bearer, seedActivity, resetDb } from '../helpers';
+
+describe('worker session lifecycle (start→pause→resume→stop→history→export)', () => {
+  beforeEach(resetDb);
+
+  it('excludes paused time, shows in history, and exports a CSV row', async () => {
+    const app = createApp();
+    const token = await authToken(app, 'lifecycle@example.com');
+    const activityId = await seedActivity('Frezen', ['Kurk']);
+
+    // start
+    const startRes = await app.request('/api/sessions/start', {
+      method: 'POST',
+      headers: bearer(token),
+      body: JSON.stringify({ activity_id: activityId, insole_type: 'Kurk', pair_count: 3 }),
+    });
+    expect(startRes.status).toBe(200);
+    const started = await startRes.json();
+
+    // pause, then backdate the pause start by 4s so resume accumulates a real span
+    await app.request(`/api/sessions/${started.id}/pause`, {
+      method: 'POST',
+      headers: bearer(token),
+    });
+    await db
+      .update(workSessions)
+      .set({ pausedAt: new Date(Date.now() - 4000) })
+      .where(eq(workSessions.id, started.id));
+    const resumeRes = await app.request(`/api/sessions/${started.id}/resume`, {
+      method: 'POST',
+      headers: bearer(token),
+    });
+    expect((await resumeRes.json()).paused_seconds).toBeGreaterThan(0);
+
+    // backdate the start by 10s so worked-time is deterministic-ish, then stop
+    await db
+      .update(workSessions)
+      .set({ startTime: new Date(Date.now() - 10000) })
+      .where(eq(workSessions.id, started.id));
+    const stopRes = await app.request(`/api/sessions/${started.id}/stop`, {
+      method: 'POST',
+      headers: bearer(token),
+    });
+    const stopped = await stopRes.json();
+    expect(stopped.status).toBe('completed');
+    expect(stopped.paused_seconds).toBeGreaterThan(0);
+    expect(stopped.duration_seconds).toBeLessThan(10); // paused time excluded
+    const wall = Math.round((Date.parse(stopped.end_time) - Date.parse(stopped.start_time)) / 1000);
+    expect(stopped.duration_seconds + stopped.paused_seconds).toBe(wall);
+
+    // history shows it
+    const hist = await (await app.request('/api/sessions', { headers: bearer(token) })).json();
+    expect(hist).toHaveLength(1);
+    expect(hist[0].id).toBe(started.id);
+    expect(hist[0].activity_name).toBe('Frezen');
+
+    // export contains the completed row
+    const csvRes = await app.request('/api/export', { headers: bearer(token) });
+    expect(csvRes.status).toBe(200);
+    const csv = await csvRes.text();
+    expect(csv).toContain('Frezen');
+    expect(csv.trim().split('\n').length).toBe(2); // header + 1 row
+  });
+});
diff --git a/apps/api/test/sessions.test.ts b/apps/api/test/sessions.test.ts
index 86881b0..8d7c4ad 100644
--- a/apps/api/test/sessions.test.ts
+++ b/apps/api/test/sessions.test.ts
@@ -441,3 +441,146 @@ describe('session reads', () => {
     expect(body[0].status).toBe('active');
   });
 });
+
+describe('session edge and error branches', () => {
+  beforeEach(resetDb);
+
+  it('400s start when the body is not valid JSON', async () => {
+    const app = createApp();
+    const token = await authToken(app, 'sess-badjson@example.com');
+
+    const res = await app.request('/api/sessions/start', {
+      method: 'POST',
+      headers: bearer(token),
+      body: '{ not json',
+    });
+    expect(res.status).toBe(400);
+  });
+
+  it('404s pause/resume/stop/discard when the id is not numeric', async () => {
+    const app = createApp();
+    const token = await authToken(app, 'sess-nan-id@example.com');
+
+    for (const action of ['pause', 'resume', 'stop', 'discard']) {
+      const res = await app.request(`/api/sessions/not-a-number/${action}`, {
+        method: 'POST',
+        headers: bearer(token),
+      });
+      expect(res.status).toBe(404);
+    }
+  });
+
+  it('409s pausing a session that is no longer active', async () => {
+    const app = createApp();
+    const token = await authToken(app, 'sess-pause-closed@example.com');
+    const activityId = await seedActivity('Frezen');
+
+    const startRes = await app.request('/api/sessions/start', {
+      method: 'POST',
+      headers: bearer(token),
+      body: JSON.stringify({ activity_id: activityId, insole_type: 'Kurk', pair_count: 2 }),
+    });
+    const started = await startRes.json();
+    await app.request(`/api/sessions/${started.id}/stop`, {
+      method: 'POST',
+      headers: bearer(token),
+    });
+
+    const res = await app.request(`/api/sessions/${started.id}/pause`, {
+      method: 'POST',
+      headers: bearer(token),
+    });
+    expect(res.status).toBe(409);
+  });
+
+  it('409s resuming a session that is no longer active', async () => {
+    const app = createApp();
+    const token = await authToken(app, 'sess-resume-closed@example.com');
+    const activityId = await seedActivity('Slijpen');
+
+    const startRes = await app.request('/api/sessions/start', {
+      method: 'POST',
+      headers: bearer(token),
+      body: JSON.stringify({ activity_id: activityId, insole_type: 'Kurk', pair_count: 2 }),
+    });
+    const started = await startRes.json();
+    await app.request(`/api/sessions/${started.id}/stop`, {
+      method: 'POST',
+      headers: bearer(token),
+    });
+
+    const res = await app.request(`/api/sessions/${started.id}/resume`, {
+      method: 'POST',
+      headers: bearer(token),
+    });
+    expect(res.status).toBe(409);
+  });
+
+  it('404s discarding a missing session', async () => {
+    const app = createApp();
+    const token = await authToken(app, 'sess-discard-missing@example.com');
+
+    const res = await app.request('/api/sessions/999999/discard', {
+      method: 'POST',
+      headers: bearer(token),
+    });
+    expect(res.status).toBe(404);
+  });
+
+  it('409s discarding an already-closed session', async () => {
+    const app = createApp();
+    const token = await authToken(app, 'sess-discard-closed@example.com');
+    const activityId = await seedActivity('Bekleden');
+
+    const startRes = await app.request('/api/sessions/start', {
+      method: 'POST',
+      headers: bearer(token),
+      body: JSON.stringify({ activity_id: activityId, insole_type: 'Kurk', pair_count: 2 }),
+    });
+    const started = await startRes.json();
+    await app.request(`/api/sessions/${started.id}/stop`, {
+      method: 'POST',
+      headers: bearer(token),
+    });
+
+    const res = await app.request(`/api/sessions/${started.id}/discard`, {
+      method: 'POST',
+      headers: bearer(token),
+    });
+    expect(res.status).toBe(409);
+  });
+
+  it('404s stopping a missing session', async () => {
+    const app = createApp();
+    const token = await authToken(app, 'sess-stop-missing@example.com');
+
+    const res = await app.request('/api/sessions/999999/stop', {
+      method: 'POST',
+      headers: bearer(token),
+    });
+    expect(res.status).toBe(404);
+  });
+
+  it("does not let user B discard user A's session (ownership scoping → 404)", async () => {
+    const app = createApp();
+    const tokenA = await authToken(app, 'sess-discard-ownerA@example.com');
+    const tokenB = await authToken(app, 'sess-discard-ownerB@example.com');
+    const activityId = await seedActivity('Printen');
+
+    const startRes = await app.request('/api/sessions/start', {
+      method: 'POST',
+      headers: bearer(tokenA),
+      body: JSON.stringify({ activity_id: activityId, insole_type: '3D', pair_count: 2 }),
+    });
+    const started = await startRes.json();
+
+    const res = await app.request(`/api/sessions/${started.id}/discard`, {
+      method: 'POST',
+      headers: bearer(tokenB),
+    });
+    expect(res.status).toBe(404);
+
+    const [row] = await db.select().from(workSessions).where(eq(workSessions.id, started.id));
+    expect(row.status).toBe('active');
+  });
+});
diff --git a/apps/api/test/work-session.test.ts b/apps/api/test/work-session.test.ts
index f899d47..4f7cadd 100644
--- a/apps/api/test/work-session.test.ts
+++ b/apps/api/test/work-session.test.ts
@@ -37,3 +37,71 @@ describe('toWorkSession paused fields', () => {
     expect(result.paused_at).toBe(pausedAt.toISOString());
   });
 });
+
+describe('toWorkSession field mapping', () => {
+  it('maps a null insoleType to null', () => {
+    const result = toWorkSession(baseRow({ insoleType: null }));
+    expect(result.insole_type).toBeNull();
+  });
+
+  it('coalesces a nullish pausedSeconds to 0 (defensive against a null column value)', () => {
+    const result = toWorkSession(baseRow({ pausedSeconds: null as unknown as number }));
+    expect(result.paused_seconds).toBe(0);
+  });
+
+  it('coalesces a nullish durationSeconds to null and a nullish notes to null', () => {
+    const result = toWorkSession(baseRow({ durationSeconds: null, notes: null }));
+    expect(result.duration_seconds).toBeNull();
+    expect(result.notes).toBeNull();
+  });
+
+  it('shapes every field, threading activity/user opts through', () => {
+    const start = new Date('2026-06-17T08:00:00.000Z');
+    const end = new Date('2026-06-17T09:30:00.000Z');
+    const created = new Date('2026-06-17T07:59:00.000Z');
+    const result = toWorkSession(
+      baseRow({
+        id: 42,
+        userId: 'user-42',
+        activityId: 7,
+        insoleType: 'Berk',
+        pairCount: 4,
+        startTime: start,
+        endTime: end,
+        durationSeconds: 5000,
+        pausedSeconds: 400,
+        status: 'completed',
+        source: 'manual',
+        notes: 'handmatig',
+        createdAt: created,
+      }),
+      { activityName: 'Frezen', userName: 'Jan', userEmail: 'jan@example.com' },
+    );
+    expect(result).toEqual({
+      id: 42,
+      user_id: 'user-42',
+      activity_id: 7,
+      activity_name: 'Frezen',
+      user_name: 'Jan',
+      user_email: 'jan@example.com',
+      insole_type: 'Berk',
+      pair_count: 4,
+      start_time: start.toISOString(),
+      end_time: end.toISOString(),
+      duration_seconds: 5000,
+      paused_seconds: 400,
+      paused_at: null,
+      status: 'completed',
+      source: 'manual',
+      notes: 'handmatig',
+      created_at: created.toISOString(),
+    });
+  });
+
+  it('defaults activity/user opts to undefined when omitted', () => {
+    const result = toWorkSession(baseRow());
+    expect(result.activity_name).toBeUndefined();
+    expect(result.user_name).toBeUndefined();
+    expect(result.user_email).toBeUndefined();
+  });
+});
diff --git a/docs/reference/domain-test-checklist.md b/docs/reference/domain-test-checklist.md
index 1306022..f8a6482 100644
--- a/docs/reference/domain-test-checklist.md
+++ b/docs/reference/domain-test-checklist.md
@@ -90,3 +90,40 @@ Guaranteed behaviors:
   unknown id).
 - Lifecycle: an admin creates three activities → reorders them → a worker's GET reflects the new
   order → the admin deletes one → it is gone from the list.
+
+## Work-sessions
+
+Src covered: `src/routes/sessions.ts` and `src/lib/work-session.ts` — both at
+100% stmts/branch/funcs/lines. The two `row.pausedSeconds ?? 0` guards in `sessions.ts`
+(resume/stop) are `c8 ignore`d with a reason — `paused_seconds` is `NOT NULL DEFAULT 0`, so the
+null branch is unreachable via any route.
+
+Guaranteed behaviors:
+
+- `start`, `pause`, `resume`, `stop`, `discard` all require a session (401 without a token), as do
+  the reads `GET /api/sessions` and `GET /api/sessions/active`.
+- `POST /api/sessions/start`: 200 creates an `active`, `source: 'app'` session (null `end_time` /
+  `duration_seconds`); 400 on an invalid body **and** on a malformed-JSON body; 404 when the
+  `activity_id` does not exist.
+- `POST /:id/pause`: 200 sets `paused_at` on a running session; 404 for a non-numeric or unknown
+  id; 409 on a double pause (already paused) and 409 when the session is no longer active.
+- `POST /:id/resume`: 200 clears `paused_at` and accumulates `paused_seconds`; 404 for a
+  non-numeric or unknown id; 409 when the session is running (not paused) and 409 when it is no
+  longer active.
+- `POST /:id/stop`: 200 completes the session, folds an open pause span into `paused_seconds`, and
+  computes `duration_seconds = wall-clock − paused_seconds` (never negative); a never-paused stop
+  keeps `paused_seconds = 0` and `duration = wall-clock`; 404 for a non-numeric/unknown id; 409
+  when already closed.
+- `POST /:id/discard`: 200 marks the session `discarded` with a null `duration_seconds`; 404 for a
+  non-numeric/unknown id; 409 when already closed.
+- Ownership scoping: user B can neither stop nor discard user A's session — both return 404 and
+  leave A's session untouched (still `active`).
+- Reads: `GET /api/sessions` returns the caller's sessions only, newest-first, joined to the
+  activity `name`; `GET /api/sessions/active` returns only that user's `active` sessions.
+- `toWorkSession` maps every field to the API contract (incl. `paused_at`, `paused_seconds`,
+  `notes`, `created_at`), threads `activity_name` / `user_name` / `user_email` opts through
+  (undefined when omitted), maps a null `insoleType` / `durationSeconds` / `notes` to null, and
+  coalesces a nullish `paused_seconds` to 0.
+- Lifecycle: start → pause → (backdate) resume accumulates paused time → (backdate) stop excludes
+  paused time from worked duration → the completed session appears in history with its activity
+  name → `GET /api/export` returns a CSV with exactly the header + one data row.