diff --git a/src/lib/withings/__tests__/sync-activity.test.ts b/src/lib/withings/__tests__/sync-activity.test.ts
index 38c5c8a9a..e0d196dd7 100644
--- a/src/lib/withings/__tests__/sync-activity.test.ts
+++ b/src/lib/withings/__tests__/sync-activity.test.ts
@@ -45,12 +45,27 @@ vi.mock("@/lib/logging/context", () => ({
   })),
 }));
 
+// v1.4.39.1 — the sync now hands its touched (type, day) keys to the
+// measurement rollup writer so the dashboard chart's `source=rollup`
+// fast-path sees the new buckets. The mock collects the call args so
+// the regression test below can assert the hook fired.
+vi.mock("@/lib/measurements/rollups", async () => {
+  const actual = await vi.importActual<
+    typeof import("@/lib/measurements/rollups")
+  >("@/lib/measurements/rollups");
+  return {
+    ...actual,
+    recomputeBucketsForMeasurement: vi.fn().mockResolvedValue(undefined),
+  };
+});
+
 import { prisma } from "@/lib/db";
 import {
   parkIntegrationAtReauth,
   recordSyncFailure,
   recordSyncSuccess,
 } from "@/lib/integrations/status";
+import { recomputeBucketsForMeasurement } from "@/lib/measurements/rollups";
 
 import { fetchWithingsActivity, syncUserActivity } from "../sync-activity";
 
@@ -363,3 +378,66 @@ describe("syncUserActivity — scope-skip guard (v1.4.26)", () => {
     expect(parkIntegrationAtReauth).not.toHaveBeenCalled();
   });
 });
+
+describe("syncUserActivity — measurement rollup hook (v1.4.39.1)", () => {
+  it("folds the persistent rollup table for each (type, day) the sync touched", async () => {
+    // Two distinct calendar days × three activity metrics each = 6
+    // writes; the rollup hook should be called once per distinct
+    // `(type, dayStart)` so the dashboard chart's `source=rollup` fast-
+    // path lights up the Withings-ingested days. Pre-v1.4.39.1 the
+    // sync skipped the hook entirely, leaving the rollup tier blind to
+    // Withings activity.
+    installFetchMock([
+      { date: "2026-05-12", steps: 8420, distance: 6720, calories: 412 },
+      { date: "2026-05-13", steps: 9100, distance: 7100, calories: 430 },
+    ]);
+    vi.mocked(prisma.measurement.findFirst).mockResolvedValue(null);
+    vi.mocked(prisma.measurement.create).mockResolvedValue({} as never);
+
+    await syncUserActivity("user-1");
+
+    expect(recomputeBucketsForMeasurement).toHaveBeenCalledTimes(6);
+    const calls = vi
+      .mocked(recomputeBucketsForMeasurement)
+      .mock.calls.map((c) => ({
+        userId: c[0],
+        type: c[1],
+        measuredAtIso: (c[2] as Date).toISOString(),
+      }));
+    // Distinct (type, day) pairs the sync touched, derived from the two
+    // dates × three metrics × `collapseToTypeDayKeys`.
+    const distinct = new Set(calls.map((c) => `${c.type}|${c.measuredAtIso}`));
+    expect(distinct.size).toBe(6);
+    expect(calls.every((c) => c.userId === "user-1")).toBe(true);
+  });
+
+  it("collapses multiple writes for the same (type, day) into a single rollup recompute", async () => {
+    // A single-date entry exercises the existing day-collapse helper —
+    // three metric rows for 2026-05-12 must fold into three rollup
+    // calls (one per type), not nine.
+    installFetchMock([
+      { date: "2026-05-12", steps: 8420, distance: 6720, calories: 412 },
+    ]);
+    vi.mocked(prisma.measurement.findFirst).mockResolvedValue(null);
+    vi.mocked(prisma.measurement.create).mockResolvedValue({} as never);
+
+    await syncUserActivity("user-1");
+
+    expect(recomputeBucketsForMeasurement).toHaveBeenCalledTimes(3);
+  });
+
+  it("swallows a populator failure so the sync still returns its imported count", async () => {
+    // The rollup recompute is a best-effort cache tier — a populator
+    // hiccup must never fail the user's sync. The sync's `imported`
+    // return value should still reflect the rows written.
+    installFetchMock([{ date: "2026-05-12", steps: 8420 }]);
+    vi.mocked(prisma.measurement.findFirst).mockResolvedValue(null);
+    vi.mocked(prisma.measurement.create).mockResolvedValue({} as never);
+    vi.mocked(recomputeBucketsForMeasurement).mockRejectedValueOnce(
+      new Error("simulated rollup failure"),
+    );
+
+    const imported = await syncUserActivity("user-1");
+    expect(imported).toBe(1);
+  });
+});
diff --git a/src/lib/withings/__tests__/sync-sleep.test.ts b/src/lib/withings/__tests__/sync-sleep.test.ts
index e79c9cfa0..04d005488 100644
--- a/src/lib/withings/__tests__/sync-sleep.test.ts
+++ b/src/lib/withings/__tests__/sync-sleep.test.ts
@@ -44,12 +44,27 @@ vi.mock("@/lib/logging/context", () => ({
   })),
 }));
 
+// v1.4.39.1 — the sleep sync now folds the persistent measurement
+// rollup tier for each touched SLEEP_DURATION day so the dashboard
+// chart's `source=rollup` fast-path sees the new segments. The mock
+// surfaces the call args for the regression test below.
+vi.mock("@/lib/measurements/rollups", async () => {
+  const actual = await vi.importActual<
+    typeof import("@/lib/measurements/rollups")
+  >("@/lib/measurements/rollups");
+  return {
+    ...actual,
+    recomputeBucketsForMeasurement: vi.fn().mockResolvedValue(undefined),
+  };
+});
+
 import { prisma } from "@/lib/db";
 import {
   parkIntegrationAtReauth,
   recordSyncFailure,
   recordSyncSuccess,
 } from "@/lib/integrations/status";
+import { recomputeBucketsForMeasurement } from "@/lib/measurements/rollups";
 
 import {
   fetchWithingsSleep,
@@ -352,3 +367,47 @@ describe("syncUserSleep — scope-skip guard (v1.4.26)", () => {
     expect(parkIntegrationAtReauth).not.toHaveBeenCalled();
   });
 });
+
+describe("syncUserSleep — measurement rollup hook (v1.4.39.1)", () => {
+  it("folds the persistent rollup table once per night the sync touched", async () => {
+    // Two distinct nights, each with multiple stage segments. The
+    // sync should collapse the per-night segments to one rollup
+    // recompute per night via `collapseToTypeDayKeys`. Pre-v1.4.39.1
+    // the rollup tier never heard about Withings sleep at all.
+    const nightA = Math.floor(Date.UTC(2026, 4, 12, 22) / 1000); // 2026-05-12 22:00 UTC
+    const nightB = Math.floor(Date.UTC(2026, 4, 13, 22) / 1000); // 2026-05-13 22:00 UTC
+    installFetchMock([
+      { startdate: nightA, enddate: nightA + 3600, state: 1, id: 1 },
+      { startdate: nightA + 3600, enddate: nightA + 5400, state: 2, id: 1 },
+      { startdate: nightA + 5400, enddate: nightA + 7200, state: 3, id: 1 },
+      { startdate: nightB, enddate: nightB + 3600, state: 1, id: 2 },
+      { startdate: nightB + 3600, enddate: nightB + 5400, state: 2, id: 2 },
+    ]);
+    vi.mocked(prisma.measurement.findFirst).mockResolvedValue(null);
+    vi.mocked(prisma.measurement.create).mockResolvedValue({} as never);
+
+    await syncUserSleep("user-1");
+
+    // Both segments of night A land in the same UTC day; night B in
+    // the next. Distinct (SLEEP_DURATION, dayStart) tuples = 2.
+    expect(recomputeBucketsForMeasurement).toHaveBeenCalledTimes(2);
+    const types = vi
+      .mocked(recomputeBucketsForMeasurement)
+      .mock.calls.map((c) => c[1]);
+    expect(new Set(types)).toEqual(new Set(["SLEEP_DURATION"]));
+  });
+
+  it("swallows a populator failure so the sync still returns its imported count", async () => {
+    installFetchMock([
+      { startdate: 1715000000, enddate: 1715003600, state: 2, id: 1 },
+    ]);
+    vi.mocked(prisma.measurement.findFirst).mockResolvedValue(null);
+    vi.mocked(prisma.measurement.create).mockResolvedValue({} as never);
+    vi.mocked(recomputeBucketsForMeasurement).mockRejectedValueOnce(
+      new Error("simulated rollup failure"),
+    );
+
+    const imported = await syncUserSleep("user-1");
+    expect(imported).toBe(1);
+  });
+});
diff --git a/src/lib/withings/sync-activity.ts b/src/lib/withings/sync-activity.ts
index f541a6b7c..b3eb3b086 100644
--- a/src/lib/withings/sync-activity.ts
+++ b/src/lib/withings/sync-activity.ts
@@ -38,6 +38,10 @@ import type { MeasurementType } from "@/generated/prisma/client";
 import { prisma } from "@/lib/db";
 import { getEvent } from "@/lib/logging/context";
 import { getUnitForType } from "@/lib/validations/measurement";
+import {
+  collapseToTypeDayKeys,
+  recomputeBucketsForMeasurement,
+} from "@/lib/measurements/rollups";
 
 import { hasActivityScope } from "./client";
 import {
@@ -285,6 +289,11 @@ export async function syncUserActivity(
   }
 
   let imported = 0;
+  // v1.4.39.1 — track every (type, measuredAt) we touched so the
+  // persistent rollup tier can be re-folded at the end of the sync.
+  // See sync.ts header for the full rationale; the chart's
+  // `source=rollup` fast-path otherwise misses Withings activity days.
+  const touched: Array<{ type: MeasurementType; measuredAt: Date }> = [];
   for (const entry of entries) {
     if (!entry.date) continue;
     const measuredAt = activityMeasuredAt(entry.date);
@@ -323,6 +332,7 @@ export async function syncUserActivity(
             },
           });
         }
+        touched.push({ type, measuredAt });
         imported++;
       } catch (err) {
         getEvent()?.addWarning(
@@ -332,6 +342,20 @@ export async function syncUserActivity(
     }
   }
 
+  // v1.4.39.1 — refresh the persistent rollup table for every distinct
+  // (type, day) the sync touched. Collapsed so a multi-day Withings
+  // catch-up costs at most ~N (type, day) recomputes.
+  try {
+    const keys = collapseToTypeDayKeys(touched);
+    for (const k of keys) {
+      await recomputeBucketsForMeasurement(userId, k.type, k.measuredAt);
+    }
+  } catch (err) {
+    getEvent()?.addWarning(
+      `withings activity: rollup recompute failed for ${userId}: ${err}`,
+    );
+  }
+
   await recordSyncSuccess(userId, "withings");
   return imported;
 }
diff --git a/src/lib/withings/sync-sleep.ts b/src/lib/withings/sync-sleep.ts
index b69f16ddf..4e85858ab 100644
--- a/src/lib/withings/sync-sleep.ts
+++ b/src/lib/withings/sync-sleep.ts
@@ -36,6 +36,10 @@ import type { MeasurementType, SleepStage } from "@/generated/prisma/client";
 import { prisma } from "@/lib/db";
 import { getEvent } from "@/lib/logging/context";
 import { getUnitForType } from "@/lib/validations/measurement";
+import {
+  collapseToTypeDayKeys,
+  recomputeBucketsForMeasurement,
+} from "@/lib/measurements/rollups";
 
 import { hasActivityScope } from "./client";
 import {
@@ -223,6 +227,10 @@ export async function syncUserSleep(
 
   let imported = 0;
   let segmentIndex = 0;
+  // v1.4.39.1 — track every (type, measuredAt) we touched so the
+  // persistent rollup tier can be re-folded at the end. See sync.ts for
+  // the full rationale.
+  const touched: Array<{ type: MeasurementType; measuredAt: Date }> = [];
   for (const segment of segments) {
     const stage = mapWithingsSleepState(segment.state);
     if (!stage) {
@@ -270,6 +278,7 @@ export async function syncUserSleep(
           },
         });
       }
+      touched.push({ type: SLEEP_TYPE, measuredAt });
       imported++;
     } catch (err) {
       getEvent()?.addWarning(
@@ -279,6 +288,20 @@ export async function syncUserSleep(
     segmentIndex++;
   }
 
+  // v1.4.39.1 — refresh the persistent rollup table for every distinct
+  // (type, day) the sync touched. Sleep segments collapse heavily —
+  // ~10 stage rows per night land in one DAY recompute.
+  try {
+    const keys = collapseToTypeDayKeys(touched);
+    for (const k of keys) {
+      await recomputeBucketsForMeasurement(userId, k.type, k.measuredAt);
+    }
+  } catch (err) {
+    getEvent()?.addWarning(
+      `withings sleep: rollup recompute failed for ${userId}: ${err}`,
+    );
+  }
+
   await recordSyncSuccess(userId, "withings");
   return imported;
 }
diff --git a/src/lib/withings/sync.ts b/src/lib/withings/sync.ts
index 9cf117105..cd6068eb6 100644
--- a/src/lib/withings/sync.ts
+++ b/src/lib/withings/sync.ts
@@ -18,6 +18,10 @@ import {
   recordSyncFailure,
   recordSyncSuccess,
 } from "@/lib/integrations/status";
+import {
+  collapseToTypeDayKeys,
+  recomputeBucketsForMeasurement,
+} from "@/lib/measurements/rollups";
 
 /**
  * Build the callback URL handed to Withings at `Notify.subscribe` time.
@@ -194,6 +198,18 @@ export async function syncUserMeasurements(
   }
 
   let imported = 0;
+  // v1.4.39.1 — track every (type, measuredAt) we touched so the
+  // persistent rollup tier can be re-folded at the end of the sync.
+  // Pre-fix, Withings-ingested BP / weight / pulse / body-fat rows
+  // skipped the rollup write hook entirely: subsequent dashboard chart
+  // fetches with `source=rollup` saw fewer DAY buckets than the live
+  // measurements table, painting the "Noch nicht genug Daten" empty
+  // state for the 30-day range on accounts whose recent data only came
+  // through Withings. We collect first, fold once at the end so a 100-
+  // row monthly catch-up costs at most ~N (type, day) recomputes rather
+  // than N per-row hooks. Best-effort: a populator hiccup never fails
+  // the user's sync.
+  const touched: Array<{ type: MeasurementType; measuredAt: Date }> = [];
 
   for (const m of measures) {
     const measType = m.type as MeasurementType;
@@ -233,12 +249,29 @@ export async function syncUserMeasurements(
           },
         });
       }
+      touched.push({ type: measType, measuredAt: m.measuredAt });
       imported++;
     } catch (err) {
       getEvent()?.addWarning(`Failed to upsert measure: ${err}`);
     }
   }
 
+  // v1.4.39.1 — refresh the persistent rollup table for every distinct
+  // (type, day) the sync touched. The chart-data + analytics read paths
+  // consume these buckets via `source=rollup`; without this hook,
+  // Withings-only metrics stayed off the rollup tier and the dashboard
+  // chart at the 30-day range under-counted recent days.
+  try {
+    const keys = collapseToTypeDayKeys(touched);
+    for (const k of keys) {
+      await recomputeBucketsForMeasurement(userId, k.type, k.measuredAt);
+    }
+  } catch (err) {
+    getEvent()?.addWarning(
+      `withings: rollup recompute failed for ${userId}: ${err}`,
+    );
+  }
+
   // Update last synced timestamp
   await prisma.withingsConnection.update({
     where: { userId },