diff --git a/src/app/api/measurements/__tests__/group-by-day.test.ts b/src/app/api/measurements/__tests__/group-by-day.test.ts
new file mode 100644
index 000000000..19e817603
--- /dev/null
+++ b/src/app/api/measurements/__tests__/group-by-day.test.ts
@@ -0,0 +1,261 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { NextRequest } from "next/server";
+
+/**
+ * v1.4.37 W7c — GET /api/measurements gains two new branches for
+ * cumulative HK types (steps, active energy, distance, flights,
+ * daylight):
+ *
+ *   1. `?type=ACTIVITY_STEPS&groupBy=day` → one synthesised row per
+ *      user-TZ day with `value` = SUM and `sampleCount` = number of
+ *      per-sample rows behind the bucket.
+ *   2. `?type=ACTIVITY_STEPS&dayKey=YYYY-MM-DD` → raw per-sample rows
+ *      for that single calendar day in the user's IANA timezone.
+ *
+ * Spot metrics (BP, weight, pulse, etc.) keep the legacy
+ * `findMany`-only behaviour even when these params are present —
+ * the schema accepts the params but the route gates each branch on
+ * `CUMULATIVE_HK_TYPES`.
+ */
+
+vi.mock("@/lib/db", () => ({
+  prisma: {
+    measurement: {
+      findMany: vi.fn(),
+      count: vi.fn(),
+    },
+    measurementRollup: {
+      findMany: vi.fn(),
+    },
+    $queryRaw: vi.fn(),
+  },
+}));
+
+vi.mock("@/lib/auth/session", () => ({ getSession: vi.fn() }));
+vi.mock("@/lib/auth/audit", () => ({ auditLog: vi.fn() }));
+vi.mock("@/lib/logging/transports", () => ({ emitIfSampled: vi.fn() }));
+vi.mock("@/lib/db-compat", () => ({
+  ensureDbCompatibility: vi.fn().mockResolvedValue(undefined),
+}));
+vi.mock("next/headers", () => ({
+  headers: vi.fn(async () => ({ get: () => null })),
+  cookies: vi.fn(async () => ({
+    get: () => undefined,
+    set: () => {},
+    delete: () => {},
+  })),
+}));
+
+import { GET } from "../route";
+import { prisma } from "@/lib/db";
+import { getSession } from "@/lib/auth/session";
+
+const SESSION_OK = {
+  session: { id: "sess-1", expiresAt: new Date(Date.now() + 3_600_000) },
+  user: {
+    id: "user-1",
+    username: "test-user",
+    role: "USER" as const,
+    timezone: "Europe/Berlin",
+  },
+};
+
+function getRequest(query: string): NextRequest {
+  return new NextRequest(`http://localhost/api/measurements?${query}`, {
+    method: "GET",
+  });
+}
+
+beforeEach(() => {
+  vi.resetAllMocks();
+  vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+});
+
+describe("GET /api/measurements — groupBy=day (W7c collapsed list)", () => {
+  it("collapses per-sample step rows into one row per user-TZ day with sampleCount", async () => {
+    // Three Apple-Watch chunks on 2026-05-15 (Europe/Berlin) +
+    // two on 2026-05-16 — the route should sum each day's bucket.
+    vi.mocked(prisma.measurement.findMany).mockResolvedValue([
+      {
+        id: "m-1",
+        type: "ACTIVITY_STEPS",
+        value: 1200,
+        unit: "steps",
+        source: "APPLE_HEALTH",
+        measuredAt: new Date("2026-05-15T08:00:00.000Z"),
+        notes: null,
+      },
+      {
+        id: "m-2",
+        type: "ACTIVITY_STEPS",
+        value: 3400,
+        unit: "steps",
+        source: "APPLE_HEALTH",
+        measuredAt: new Date("2026-05-15T11:00:00.000Z"),
+        notes: null,
+      },
+      {
+        id: "m-3",
+        type: "ACTIVITY_STEPS",
+        value: 800,
+        unit: "steps",
+        source: "APPLE_HEALTH",
+        measuredAt: new Date("2026-05-15T16:00:00.000Z"),
+        notes: null,
+      },
+      {
+        id: "m-4",
+        type: "ACTIVITY_STEPS",
+        value: 2500,
+        unit: "steps",
+        source: "APPLE_HEALTH",
+        measuredAt: new Date("2026-05-16T07:00:00.000Z"),
+        notes: null,
+      },
+      {
+        id: "m-5",
+        type: "ACTIVITY_STEPS",
+        value: 4500,
+        unit: "steps",
+        source: "APPLE_HEALTH",
+        measuredAt: new Date("2026-05-16T14:00:00.000Z"),
+        notes: null,
+      },
+    ] as never);
+
+    const res = await GET(
+      getRequest(
+        "type=ACTIVITY_STEPS&groupBy=day&from=2026-05-15T00:00:00Z&to=2026-05-17T00:00:00Z",
+      ),
+    );
+    expect(res.status).toBe(200);
+    const json = (await res.json()) as {
+      data: {
+        measurements: Array<{
+          type: string;
+          value: number;
+          unit: string;
+          dayKey: string;
+          sampleCount: number;
+          measuredAt: string;
+        }>;
+        meta: { groupBy?: string; total: number };
+      };
+    };
+    expect(json.data.meta.groupBy).toBe("day");
+    expect(json.data.measurements.length).toBe(2);
+    // Sort is desc by default — newer day first.
+    const [day16, day15] = json.data.measurements;
+    expect(day16.dayKey).toBe("2026-05-16");
+    expect(day16.value).toBe(7000);
+    expect(day16.sampleCount).toBe(2);
+    expect(day16.unit).toBe("steps");
+    expect(day15.dayKey).toBe("2026-05-15");
+    expect(day15.value).toBe(5400);
+    expect(day15.sampleCount).toBe(3);
+    // The collapsed row's measuredAt anchors to local noon so the
+    // row sorts cleanly between same-day spot samples (canonical
+    // daily-timestamp contract shared with the drain helper).
+    expect(day15.measuredAt).toContain("2026-05-15T10:00:00");
+  });
+
+  it("falls back to the legacy findMany path when groupBy=day is set on a non-cumulative type", async () => {
+    vi.mocked(prisma.measurement.findMany).mockResolvedValue([
+      {
+        id: "m-1",
+        type: "PULSE",
+        value: 60,
+        unit: "bpm",
+        source: "MANUAL",
+        measuredAt: new Date("2026-05-15T09:00:00.000Z"),
+        notes: null,
+      },
+    ] as never);
+    vi.mocked(prisma.measurement.count).mockResolvedValue(1 as never);
+
+    const res = await GET(getRequest("type=PULSE&groupBy=day"));
+    expect(res.status).toBe(200);
+    const json = (await res.json()) as {
+      data: {
+        measurements: Array<{ type: string }>;
+        meta: { groupBy?: string };
+      };
+    };
+    // Spot metrics keep the per-sample shape; the collapse branch
+    // never fires.
+    expect(json.data.meta.groupBy).toBeUndefined();
+    expect(json.data.measurements.length).toBe(1);
+  });
+});
+
+describe("GET /api/measurements — dayKey drill-down (W7c)", () => {
+  it("returns per-sample rows for the requested calendar day in the user's TZ", async () => {
+    vi.mocked(prisma.measurement.findMany).mockResolvedValue([
+      {
+        id: "m-1",
+        type: "ACTIVITY_STEPS",
+        value: 1200,
+        unit: "steps",
+        source: "APPLE_HEALTH",
+        measuredAt: new Date("2026-05-15T08:00:00.000Z"),
+        notes: null,
+      },
+      {
+        id: "m-2",
+        type: "ACTIVITY_STEPS",
+        value: 3400,
+        unit: "steps",
+        source: "APPLE_HEALTH",
+        measuredAt: new Date("2026-05-15T15:00:00.000Z"),
+        notes: null,
+      },
+    ] as never);
+
+    const res = await GET(
+      getRequest("type=ACTIVITY_STEPS&dayKey=2026-05-15"),
+    );
+    expect(res.status).toBe(200);
+    const json = (await res.json()) as {
+      data: {
+        measurements: Array<{ id: string; value: number }>;
+        meta: { dayKey?: string };
+      };
+    };
+    expect(json.data.meta.dayKey).toBe("2026-05-15");
+    expect(json.data.measurements.length).toBe(2);
+    expect(json.data.measurements[0].value).toBe(1200);
+
+    // The route resolves the user-TZ day boundary, so the underlying
+    // findMany must be called with measuredAt: { gte, lt } shape.
+    const call = vi.mocked(prisma.measurement.findMany).mock.calls[0]?.[0];
+    expect(call).toBeDefined();
+    const measuredAt = (call as { where: { measuredAt?: unknown } }).where
+      .measuredAt as { gte?: Date; lt?: Date };
+    expect(measuredAt.gte).toBeInstanceOf(Date);
+    expect(measuredAt.lt).toBeInstanceOf(Date);
+    // Window is exactly 24 hours wide for any whole-hour-offset zone.
+    expect(measuredAt.lt!.getTime() - measuredAt.gte!.getTime()).toBe(
+      24 * 60 * 60 * 1000,
+    );
+  });
+
+  it("rejects a malformed dayKey at the validation gate (no DB call)", async () => {
+    const res = await GET(getRequest("type=ACTIVITY_STEPS&dayKey=15.05.2026"));
+    expect(res.status).toBe(422);
+    expect(prisma.measurement.findMany).not.toHaveBeenCalled();
+  });
+
+  it("ignores dayKey on non-cumulative types and falls back to the legacy path", async () => {
+    vi.mocked(prisma.measurement.findMany).mockResolvedValue([] as never);
+    vi.mocked(prisma.measurement.count).mockResolvedValue(0 as never);
+
+    const res = await GET(getRequest("type=PULSE&dayKey=2026-05-15"));
+    expect(res.status).toBe(200);
+    const json = (await res.json()) as {
+      data: { meta: { dayKey?: string } };
+    };
+    // No dayKey echo on the legacy path — proves the W7c branch
+    // didn't fire for the spot metric.
+    expect(json.data.meta.dayKey).toBeUndefined();
+  });
+});
diff --git a/src/components/measurements/__tests__/measurement-list-step-grouping.test.tsx b/src/components/measurements/__tests__/measurement-list-step-grouping.test.tsx
new file mode 100644
index 000000000..d30eebbb2
--- /dev/null
+++ b/src/components/measurements/__tests__/measurement-list-step-grouping.test.tsx
@@ -0,0 +1,108 @@
+import { describe, expect, it, vi } from "vitest";
+import { renderToStaticMarkup } from "react-dom/server";
+
+/**
+ * v1.4.37 W7c — when the list filter is a cumulative HK type, the
+ * list view renders one row per user-TZ day with the day's total and
+ * a chevron that drills back into the per-sample chunks via a
+ * separate query. This test mocks both queries (the parent + the
+ * drill-down) and asserts the rendered surface paints the collapsed
+ * shape without leaking per-sample rows by default.
+ */
+
+const collapsed = [
+  {
+    id: "day:ACTIVITY_STEPS:2026-05-15",
+    type: "ACTIVITY_STEPS",
+    value: 12000,
+    unit: "steps",
+    source: "APPLE_HEALTH",
+    measuredAt: "2026-05-15T10:00:00.000Z",
+    notes: null,
+    dayKey: "2026-05-15",
+    sampleCount: 42,
+  },
+];
+
+// Per-mock TanStack Query stub: when the queryKey starts with
+// "measurement-drilldown" we serve nothing (drill-down should not
+// fire until the chevron is clicked, which static render never
+// triggers).
+vi.mock("@tanstack/react-query", () => ({
+  useQuery: ({ queryKey }: { queryKey: unknown[] }) => {
+    if (
+      Array.isArray(queryKey) &&
+      queryKey[0] === "measurement-drilldown"
+    ) {
+      return { data: undefined, isLoading: false };
+    }
+    return {
+      data: { measurements: collapsed, meta: { total: 1 } },
+      isLoading: false,
+    };
+  },
+  useQueryClient: () => ({ invalidateQueries: vi.fn() }),
+  useMutation: () => ({
+    mutate: vi.fn(),
+    mutateAsync: vi.fn(),
+    isPending: false,
+    isError: false,
+    error: null,
+  }),
+}));
+
+vi.mock("next/navigation", () => ({
+  useRouter: () => ({ push: vi.fn(), replace: vi.fn() }),
+  usePathname: () => "/measurements",
+}));
+
+vi.mock("@/hooks/use-auth", () => ({
+  useAuth: () => ({
+    user: { id: "u1", username: "marc", role: "USER" },
+    isAuthenticated: true,
+    isLoading: false,
+  }),
+}));
+
+import { I18nProvider } from "@/lib/i18n/context";
+import { MeasurementList } from "../measurement-list";
+
+function render(locale: "en" | "de" = "en") {
+  return renderToStaticMarkup(
+    <I18nProvider initialLocale={locale}>
+      <MeasurementList />
+    </I18nProvider>,
+  );
+}
+
+describe("MeasurementList — cumulative-type collapsed view (W7c)", () => {
+  it("renders the daily-total caption with the sample count", () => {
+    const html = render("en");
+    // The daily-total caption ("(42 samples)") sits next to the
+    // day's total ("12000 steps") on the collapsed row.
+    expect(html).toContain("12,000 steps");
+    expect(html).toMatch(/\(42 samples\)/);
+  });
+
+  it("renders a chevron-expand button on the collapsed row", () => {
+    const html = render("en");
+    expect(html).toContain('data-testid="measurement-day-expand"');
+    // The chevron exposes its expanded state via aria-expanded so
+    // assistive tech announces the toggle correctly.
+    expect(html).toMatch(/aria-expanded="false"/);
+  });
+
+  it("does not paint edit/delete affordances on the synthesised daily row", () => {
+    const html = render("en");
+    // The edit + delete actions are hidden because the synthetic
+    // `day:…` id has no real Measurement row backing it. The chevron
+    // is the only action.
+    expect(html).not.toMatch(/aria-label="Edit"/);
+    expect(html).not.toMatch(/aria-label="Delete"/);
+  });
+
+  it("localises the daily-total caption in German", () => {
+    const html = render("de");
+    expect(html).toMatch(/\(42 Einzelwerte\)/);
+  });
+});
diff --git a/src/lib/jobs/__tests__/drain-cumulative-queue.test.ts b/src/lib/jobs/__tests__/drain-cumulative-queue.test.ts
new file mode 100644
index 000000000..349d08bce
--- /dev/null
+++ b/src/lib/jobs/__tests__/drain-cumulative-queue.test.ts
@@ -0,0 +1,53 @@
+/**
+ * v1.4.37 W7c — pg-boss queue registration for the nightly drain of
+ * per-sample APPLE_HEALTH cumulative rows. The drain helper exists
+ * since v1.4.30 but only ran via the admin endpoint / CLI; the
+ * scheduled wrapper closes the loop so the list view stops painting
+ * hundreds of step chunks per day.
+ *
+ * Same source-text-grep approach as the Withings queue regression
+ * guard so we never have to boot pg-boss + Prisma to assert the
+ * scheduler wiring stays intact.
+ */
+import { readFileSync } from "node:fs";
+import { join } from "node:path";
+
+import { describe, expect, it } from "vitest";
+
+const REMINDER_WORKER_PATH = join(__dirname, "..", "reminder-worker.ts");
+const source = readFileSync(REMINDER_WORKER_PATH, "utf8");
+
+describe("reminder-worker — drainPerSampleCumulative nightly schedule", () => {
+  it("declares the drain queue at the documented Berlin cadence", () => {
+    expect(source).toMatch(
+      /DRAIN_CUMULATIVE_QUEUE\s*=\s*["']drain-per-sample-cumulative["']/,
+    );
+    // 03:45 Europe/Berlin — between audit-log cleanup (03:15) and the
+    // feedback aggregator (04:00). Keep the slot stable so an operator
+    // staring at the cron table can find the job easily.
+    expect(source).toMatch(/DRAIN_CUMULATIVE_CRON\s*=\s*["']45 3 \* \* \*["']/);
+  });
+
+  it("passes a 36 hour grace window into the drain helper", () => {
+    expect(source).toMatch(/DRAIN_CUMULATIVE_CUTOFF_HOURS\s*=\s*36/);
+    expect(source).toMatch(/cutoffHours:\s*DRAIN_CUMULATIVE_CUTOFF_HOURS/);
+  });
+
+  it("imports drainPerSampleCumulative from the existing helper module", () => {
+    expect(source).toMatch(
+      /import\s*\{\s*drainPerSampleCumulative\s*\}\s*from\s*["']@\/lib\/measurements\/drain-per-sample-cumulative["']/,
+    );
+  });
+
+  it("registers a boss.work handler against the drain queue", () => {
+    expect(source).toMatch(
+      /boss\.work[\s\S]{0,200}DRAIN_CUMULATIVE_QUEUE[\s\S]{0,400}drainPerSampleCumulative/,
+    );
+  });
+
+  it("schedules the drain cron via boss.schedule (allQueues + schedules)", () => {
+    expect(source).toMatch(
+      /\[DRAIN_CUMULATIVE_QUEUE,\s*DRAIN_CUMULATIVE_CRON\]/,
+    );
+  });
+});
diff --git a/src/lib/measurements/__tests__/drain-per-sample-cumulative.test.ts b/src/lib/measurements/__tests__/drain-per-sample-cumulative.test.ts
index db340f475..8aa2fcb83 100644
--- a/src/lib/measurements/__tests__/drain-per-sample-cumulative.test.ts
+++ b/src/lib/measurements/__tests__/drain-per-sample-cumulative.test.ts
@@ -1,11 +1,13 @@
-import { describe, expect, it } from "vitest";
+import { describe, expect, it, vi } from "vitest";
 
 import {
   bucketRowsByUserDay,
   canonicalDailyTimestamp,
   dayKeyForUserTz,
+  drainPerSampleCumulative,
   sumBucketValues,
 } from "../drain-per-sample-cumulative";
+import type { PrismaClient } from "@/generated/prisma/client";
 
 describe("dayKeyForUserTz", () => {
   it("anchors the calendar day to the user's IANA zone", () => {
@@ -152,3 +154,83 @@ describe("sumBucketValues", () => {
     expect(sumBucketValues(rows)).toBeCloseTo(20.0);
   });
 });
+
+// v1.4.37 W7c — the scheduled nightly drain passes a 36 h grace
+// window so today + the trailing watch-sync reconciliation period
+// stay per-sample for the list view. The test below pins that the
+// cutoffHours option filters by `measuredAt: { lt: cutoff }` rather
+// than collapsing every row in sight.
+describe("drainPerSampleCumulative — cutoffHours", () => {
+  function buildPrismaMock() {
+    const findManyUser = vi.fn();
+    const findManyMeasurement = vi.fn().mockResolvedValue([]);
+    return {
+      user: { findMany: findManyUser },
+      measurement: { findMany: findManyMeasurement },
+      $transaction: vi.fn(async (cb: (tx: unknown) => Promise<unknown>) =>
+        cb({}),
+      ),
+    } as unknown as PrismaClient & {
+      user: { findMany: ReturnType<typeof vi.fn> };
+      measurement: { findMany: ReturnType<typeof vi.fn> };
+    };
+  }
+
+  it("passes a measuredAt cutoff into the per-sample findMany when cutoffHours is set", async () => {
+    const prismaMock = buildPrismaMock();
+    prismaMock.user.findMany.mockResolvedValue([
+      { id: "user-1", timezone: "Europe/Berlin" },
+    ]);
+
+    const beforeAt = Date.now();
+    await drainPerSampleCumulative(prismaMock, {
+      cutoffHours: 36,
+      log: () => {},
+    });
+    const afterAt = Date.now();
+
+    // The helper iterates every cumulative type — assert the first
+    // findMany call carries the expected cutoff filter shape.
+    const call = prismaMock.measurement.findMany.mock.calls[0]?.[0];
+    expect(call).toBeDefined();
+    expect(call.where.source).toBe("APPLE_HEALTH");
+    expect(call.where.measuredAt?.lt).toBeInstanceOf(Date);
+
+    const cutoff = call.where.measuredAt!.lt as Date;
+    const expectedMin = beforeAt - 36 * 60 * 60 * 1000;
+    const expectedMax = afterAt - 36 * 60 * 60 * 1000;
+    expect(cutoff.getTime()).toBeGreaterThanOrEqual(expectedMin);
+    expect(cutoff.getTime()).toBeLessThanOrEqual(expectedMax);
+  });
+
+  it("omits the cutoff filter when cutoffHours is not provided (CLI / admin one-shot)", async () => {
+    const prismaMock = buildPrismaMock();
+    prismaMock.user.findMany.mockResolvedValue([
+      { id: "user-1", timezone: "Europe/Berlin" },
+    ]);
+
+    await drainPerSampleCumulative(prismaMock, { log: () => {} });
+
+    const call = prismaMock.measurement.findMany.mock.calls[0]?.[0];
+    expect(call).toBeDefined();
+    expect(call.where.source).toBe("APPLE_HEALTH");
+    // Legacy callers (CLI, admin endpoint) must keep the all-rows
+    // behaviour so a backfill drains everything the operator asked for.
+    expect(call.where.measuredAt).toBeUndefined();
+  });
+
+  it("ignores a zero cutoffHours value (treat 0 as not-set)", async () => {
+    const prismaMock = buildPrismaMock();
+    prismaMock.user.findMany.mockResolvedValue([
+      { id: "user-1", timezone: "Europe/Berlin" },
+    ]);
+
+    await drainPerSampleCumulative(prismaMock, {
+      cutoffHours: 0,
+      log: () => {},
+    });
+
+    const call = prismaMock.measurement.findMany.mock.calls[0]?.[0];
+    expect(call.where.measuredAt).toBeUndefined();
+  });
+});