diff --git a/docs/integrations/google-health.md b/docs/integrations/google-health.md
index 7fc61e208..b9bf5e095 100644
--- a/docs/integrations/google-health.md
+++ b/docs/integrations/google-health.md
@@ -122,22 +122,87 @@ The Google Cloud client id/secret are per-user (Settings), not env vars.
 
 ## Backfill, the hourly sync and Google's rate limit
 
-Only one sync runs per account at a time. While the history backfill that
-follows a connect is running, the hourly sync leaves that account alone, and
-**Sync now** reports that a sync is already in progress and shows its progress
-instead of starting a second one.
+Only one sync runs per account at a time. **Sync now** reports that a sync is
+already in progress while the history backfill that follows a connect is
+running, and shows its progress instead of starting a second one.
+
+The backfill reads the account's whole history, and for a watch that records
+heart rate every minute that is a thousand-odd pages per year. It runs in
+slices: a slice reads for up to five minutes or 500 pages, writes what it
+read, notes how far it got and lets go of the account. The next slice starts
+a minute later where the last one stopped. Two kinds of note are kept: a data
+type read to the end is not read again, and a data type read page by page
+(heart rate, weight, body fat, blood glucose, core temperature) keeps the
+time of the oldest reading it has written, so the next slice asks Google only
+for what is older. A restart or an update in the middle loses at most the page
+that was being read.
+
+The hourly sync waits for the slice that is running (up to eight minutes)
+instead of skipping the account, so recent data keeps arriving while an old
+history is still coming in.
 
 Google limits how many requests one account may make per minute. When a sync
-reaches that limit, Google answers `429`, and HealthLog waits and repeats the
-request; the connection is never marked as needing a reconnect because of it.
-Access tokens last an hour, and a long backfill renews its token as it goes.
-A backfill that stops part-way (a restart, the job's time budget) picks up
-with the data types it has not finished yet on its next attempt.
+reaches that limit Google answers `429`, and HealthLog waits and repeats the
+request. If Google asks for a longer wait than a minute, the slice ends there
+and the next one starts five minutes later. A server error (`500`, `502`,
+`503`, `504`), a request that times out and a dropped connection are repeated
+three times before they count as a failure. None of these mark the connection
+as needing a reconnect. Access tokens last an hour, and a long backfill renews
+its token as it goes.
+
+A slice that moved nothing forward (no data type finished, no reading older
+than before) is a real failure: the job fails with the reason, pg-boss retries
+it a few times, and after that the next restart offers the backfill again.
+Everything already written stays.
 
 If an older version left your Google Health card asking for a reconnect after
 a backfill, the first sync after updating checks the stored grant and resumes
 on its own when the grant is still valid.
 
+### Reading the backfill in the logs
+
+Every slice writes one log line when it ends, with
+`"background":{"task_name":"job.integration_backfill"}`. The parts worth
+reading:
+
+- `meta.kind` is `google-health-backfill`, `meta.slice` the slice number
+  (0 for the first), `meta.job_id` the pg-boss job.
+- `external_calls` lists the requests the slice made to Google, one entry per
+  request: `method` names the data type and page (`fetchHeartRate(page=212)`),
+  `status` the HTTP status, `duration_ms` how long it took. A request that was
+  repeated carries a `note` (`rate_limited_retrying_in_ms=4000`,
+  `server_error_retrying_in_ms=2000`, `no_response_retrying_in_ms=2000`,
+  `token_rejected_retrying_with_fresh_token`); one that failed for good
+  carries an `error`. Successful requests are listed up to 60 per line and
+  everything up to 200; `external_calls_omitted` counts the rest.
+- `meta["googleHealth.backfill.slice"]` sums the slice up:
+  - `pages`, `elapsedMs` and `imported`: what the slice read, how long it
+    took, how many readings it wrote.
+  - `stopReason`: why it ended early. `time_budget` and `page_budget` are the
+    normal end of a slice, `rate_limited` means Google would not take more
+    requests for now, `job_budget` that the job itself ran out of time.
+    `null` means the slice read everything it started.
+  - `collectionsDone` of `collectionsTotal`: data types read to the end so
+    far.
+  - `collections`: one entry per data type the slice touched, with its
+    `status` (`done`, `stopped` short on a budget or a rate limit,
+    `deferred` to the next slice, or `failed`), its `pages`, and for the
+    page-by-page types
+    `edgeFrom` and `edgeTo`, the oldest reading written before and after the
+    slice.
+  - `edges`: where every unfinished page-by-page data type stands now.
+- `action.name` is `google_health.backfill.continued` for a slice that made
+  progress and queued the next one, `google_health.backfill.complete` for the
+  one that finished the history, and `google_health.backfill.stuck` for one
+  that moved nothing. A stuck slice also fails the job with a message that
+  names each unfinished data type and its status, for example
+  `no progress in slice 4, stopped on rate_limited; fetchHeartRate:stopped`.
+
+While a slice runs, the usual `job.progress` line for the
+`integration-backfill-admission` queue reports
+`google_health_backfill_slice`, `google_health_backfill_pages` and
+`google_health_backfill_collections_done` every two minutes.
+
 ## The 7-day re-consent caveat
 
 While the OAuth consent screen stays in **Testing** publishing mode, Google
diff --git a/prisma/schema.prisma b/prisma/schema.prisma
index 9834872e9..95b316c3a 100644
--- a/prisma/schema.prisma
+++ b/prisma/schema.prisma
@@ -4410,8 +4410,10 @@ model GoogleHealthConnection {
   /// pre-fix externalId (a re-scored night minted parallel copies). Null =
   /// repair pending (or the connection predates the fix).
   sleepRepairedAt     DateTime? @map("sleep_repaired_at")
-  /// The collections the in-flight history backfill has already walked to
-  /// the end (`{ done: string[] }`), so a retry resumes with the rest
+  /// How far the in-flight history backfill has got
+  /// (`{ done: string[], cursors: { [collection]: { at, order, pages } } }`):
+  /// the collections it walked to the end, and for each collection read page
+  /// by page the edge it has written up to, so the next slice resumes there
   /// instead of starting over. Null once the backfill completes, and reset
   /// on every reconnect.
   backfillProgress    Json?     @map("backfill_progress")
diff --git a/src/lib/google-health/__tests__/backfill-resume-progress.test.ts b/src/lib/google-health/__tests__/backfill-resume-progress.test.ts
index aa80d605d..69e9715e9 100644
--- a/src/lib/google-health/__tests__/backfill-resume-progress.test.ts
+++ b/src/lib/google-health/__tests__/backfill-resume-progress.test.ts
@@ -20,9 +20,17 @@ vi.mock("@/lib/logging/context", () => ({
 }));
 
 import {
+  readGoogleHealthBackfillCursors,
+  recordGoogleHealthBackfillPage,
   runGoogleHealthCollection,
   runWithGoogleHealthBackfillResume,
+  type GoogleHealthBackfillCursor,
 } from "../sync-core";
+import {
+  googleHealthSliceBudget,
+  runWithGoogleHealthClientOutcome,
+  runWithGoogleHealthStop,
+} from "../client";
 
 beforeEach(() => {
   vi.clearAllMocks();
@@ -41,7 +49,9 @@ describe("runGoogleHealthCollection under a backfill", () => {
     expect([...done]).toEqual(["fetchSteps", "sleep"]);
     expect(prismaMock.googleHealthConnection.update).toHaveBeenCalledWith({
       where: { userId: "u1" },
-      data: { backfillProgress: { done: ["fetchSteps", "sleep"] } },
+      data: {
+        backfillProgress: { done: ["fetchSteps", "sleep"], cursors: {} },
+      },
     });
   });
 
@@ -63,3 +73,183 @@ describe("runGoogleHealthCollection under a backfill", () => {
     );
   });
 });
+
+/**
+ * #1220 — a collection read page by page keeps its place inside the
+ * collection, not only once it is finished. A heart-rate history of years
+ * that one attempt could not finish used to start over from its newest page
+ * on every attempt.
+ */
+describe("the resume edge of a page-by-page collection", () => {
+  const at = (iso: string) => new Date(iso);
+
+  it("moves the edge to the oldest sample of each page and persists it", async () => {
+    prismaMock.googleHealthConnection.update.mockResolvedValue({});
+    const cursors = new Map<string, GoogleHealthBackfillCursor>();
+
+    const { advanced } = await runWithGoogleHealthBackfillResume(
+      "u1",
+      new Set(["sleep"]),
+      async () => {
+        await recordGoogleHealthBackfillPage("fetchHeartRate", {
+          first: at("2026-10-01T12:00:00Z"),
+          last: at("2026-10-01T00:00:00Z"),
+        });
+        await recordGoogleHealthBackfillPage("fetchHeartRate", {
+          first: at("2026-09-30T23:59:00Z"),
+          last: at("2026-09-30T08:00:00Z"),
+        });
+      },
+      cursors,
+    );
+
+    expect(cursors.get("fetchHeartRate")).toEqual({
+      at: "2026-09-30T08:00:00.000Z",
+      order: "desc",
+      pages: 2,
+    });
+    expect(advanced.get("fetchHeartRate")).toBeNull();
+    const last = prismaMock.googleHealthConnection.update.mock.calls.at(
+      -1,
+    )![0] as { data: { backfillProgress: unknown } };
+    expect(last.data.backfillProgress).toEqual({
+      done: ["sleep"],
+      cursors: {
+        fetchHeartRate: {
+          at: "2026-09-30T08:00:00.000Z",
+          order: "desc",
+          pages: 2,
+        },
+      },
+    });
+    // And it reads back the way it was written.
+    expect(
+      readGoogleHealthBackfillCursors(last.data.backfillProgress).get(
+        "fetchHeartRate",
+      ),
+    ).toEqual(cursors.get("fetchHeartRate"));
+  });
+
+  it("follows a walk that runs oldest first", async () => {
+    prismaMock.googleHealthConnection.update.mockResolvedValue({});
+    const cursors = new Map<string, GoogleHealthBackfillCursor>();
+    await runWithGoogleHealthBackfillResume(
+      "u1",
+      new Set(),
+      () =>
+        recordGoogleHealthBackfillPage("fetchWeight", {
+          first: at("2024-01-01T00:00:00Z"),
+          last: at("2024-03-01T00:00:00Z"),
+        }),
+      cursors,
+    );
+    expect(cursors.get("fetchWeight")).toMatchObject({
+      at: "2024-03-01T00:00:00.000Z",
+      order: "asc",
+    });
+  });
+
+  it("does not count a page that moved nothing as progress", async () => {
+    prismaMock.googleHealthConnection.update.mockResolvedValue({});
+    const cursors = new Map<string, GoogleHealthBackfillCursor>([
+      [
+        "fetchHeartRate",
+        { at: "2026-01-01T00:00:00.000Z", order: "desc", pages: 7 },
+      ],
+    ]);
+    const { advanced } = await runWithGoogleHealthBackfillResume(
+      "u1",
+      new Set(),
+      () =>
+        // The edge sample itself, read again: no further than before.
+        recordGoogleHealthBackfillPage("fetchHeartRate", {
+          first: at("2026-01-01T00:00:00Z"),
+          last: at("2026-01-01T00:00:00Z"),
+        }),
+      cursors,
+    );
+    expect(advanced.size).toBe(0);
+    expect(cursors.get("fetchHeartRate")).toMatchObject({
+      at: "2026-01-01T00:00:00.000Z",
+      pages: 8,
+    });
+  });
+
+  it("counts no progress when the edge cannot be written", async () => {
+    prismaMock.googleHealthConnection.update.mockRejectedValue(
+      new Error("connection reset"),
+    );
+    const cursors = new Map<string, GoogleHealthBackfillCursor>();
+    const { advanced } = await runWithGoogleHealthBackfillResume(
+      "u1",
+      new Set(),
+      () =>
+        recordGoogleHealthBackfillPage("fetchHeartRate", {
+          first: at("2026-10-01T12:00:00Z"),
+          last: at("2026-10-01T00:00:00Z"),
+        }),
+      cursors,
+    );
+    expect(advanced.size).toBe(0);
+    expect(cursors.size).toBe(0);
+    expect(warnings.some((w) => w.includes("progress write failed"))).toBe(
+      true,
+    );
+  });
+
+  it("clears a finished collection's edge with the same write that marks it done", async () => {
+    prismaMock.googleHealthConnection.update.mockResolvedValue({});
+    const cursors = new Map<string, GoogleHealthBackfillCursor>([
+      [
+        "fetchHeartRate",
+        { at: "2026-01-01T00:00:00.000Z", order: "desc", pages: 7 },
+      ],
+    ]);
+    const done = new Set<string>();
+    await runWithGoogleHealthBackfillResume(
+      "u1",
+      done,
+      () => runGoogleHealthCollection("fetchHeartRate", async () => 1),
+      cursors,
+    );
+    expect([...done]).toEqual(["fetchHeartRate"]);
+    expect(cursors.size).toBe(0);
+    expect(prismaMock.googleHealthConnection.update).toHaveBeenCalledWith({
+      where: { userId: "u1" },
+      data: { backfillProgress: { done: ["fetchHeartRate"], cursors: {} } },
+    });
+  });
+
+  it("leaves a collection for the next slice once the slice has no budget left", async () => {
+    prismaMock.googleHealthConnection.update.mockResolvedValue({});
+    const walk = vi.fn(async () => 5);
+    const budget = googleHealthSliceBudget(0, 100);
+    const { result } = await runWithGoogleHealthClientOutcome(() =>
+      runWithGoogleHealthBackfillResume("u1", new Set(), () =>
+        runWithGoogleHealthStop(
+          () => false,
+          () => runGoogleHealthCollection("fetchHeartRate", walk),
+          budget,
+        ),
+      ),
+    );
+    expect(walk).not.toHaveBeenCalled();
+    expect(result.collections).toEqual([
+      { key: "fetchHeartRate", status: "deferred", pages: 0, durationMs: 0 },
+    ]);
+    expect(budget.stopReason).toBe("time_budget");
+  });
+
+  it("marks the cycle incomplete when it leaves a collection for later", async () => {
+    const { outcome } = await runWithGoogleHealthClientOutcome(() =>
+      runWithGoogleHealthBackfillResume("u1", new Set(), () =>
+        runWithGoogleHealthStop(
+          () => false,
+          () => runGoogleHealthCollection("fetchWeight", async () => 0),
+          googleHealthSliceBudget(0, 100),
+        ),
+      ),
+    );
+    expect(outcome.truncated).toBe(true);
+  });
+});
diff --git a/src/lib/google-health/__tests__/rollup-request.test.ts b/src/lib/google-health/__tests__/rollup-request.test.ts
index 54e23c31b..bed00a773 100644
--- a/src/lib/google-health/__tests__/rollup-request.test.ts
+++ b/src/lib/google-health/__tests__/rollup-request.test.ts
@@ -208,7 +208,8 @@ describe("fetchDailyRollUp — chunk walk + conservative fallback", () => {
   });
 
   it("propagates a non-400 first-request failure without a fallback walk", async () => {
-    safeFetchMock.mockResolvedValueOnce(jsonResponse(500, {}));
+    // A 403 is neither the fallback's 400 nor a server error worth repeating.
+    safeFetchMock.mockResolvedValueOnce(jsonResponse(403, {}));
     await expect(
       fetchDailyRollUp(GOOGLE_HEALTH_DATA_TYPES.steps, "token", "fetchSteps", {
         start: new Date("2026-06-01T00:00:00Z"),
diff --git a/src/lib/google-health/__tests__/sync-metrics-dense-pages.test.ts b/src/lib/google-health/__tests__/sync-metrics-dense-pages.test.ts
index b4bf66c8e..becd43db9 100644
--- a/src/lib/google-health/__tests__/sync-metrics-dense-pages.test.ts
+++ b/src/lib/google-health/__tests__/sync-metrics-dense-pages.test.ts
@@ -32,6 +32,10 @@ vi.mock("../sync-core", () => ({
     (_userId: string, info: { accessToken: string }) => async () =>
       info.accessToken,
   runGoogleHealthCollection: (_key: string, fn: () => Promise<number>) => fn(),
+  // Outside a backfill: no resume edge, nothing to record.
+  googleHealthBackfillCursor: () => null,
+  googleHealthHardFailureCount: () => 0,
+  recordGoogleHealthBackfillPage: vi.fn(async () => {}),
 }));
 
 vi.mock("@/lib/db", () => ({
diff --git a/src/lib/google-health/__tests__/sync-metrics-failsoft.test.ts b/src/lib/google-health/__tests__/sync-metrics-failsoft.test.ts
index 0a4c021e0..1f0ce79d2 100644
--- a/src/lib/google-health/__tests__/sync-metrics-failsoft.test.ts
+++ b/src/lib/google-health/__tests__/sync-metrics-failsoft.test.ts
@@ -58,6 +58,10 @@ vi.mock("../sync-core", () => ({
     (_userId: string, info: { accessToken: string }) => async () =>
       info.accessToken,
   runGoogleHealthCollection: (_key: string, fn: () => Promise<number>) => fn(),
+  // Outside a backfill: no resume edge, nothing to record.
+  googleHealthBackfillCursor: () => null,
+  googleHealthHardFailureCount: () => 0,
+  recordGoogleHealthBackfillPage: vi.fn(async () => {}),
   upsertGoogleHealthMeasurements: vi.fn(async () => ({
     imported: 0,
     touched: [],
diff --git a/src/lib/google-health/__tests__/walk-resume-and-retry.test.ts b/src/lib/google-health/__tests__/walk-resume-and-retry.test.ts
new file mode 100644
index 000000000..ecaba31c6
--- /dev/null
+++ b/src/lib/google-health/__tests__/walk-resume-and-retry.test.ts
@@ -0,0 +1,192 @@
+/**
+ * #1220 — the list walk under a backfill slice.
+ *
+ *   - A server error or a request that got no answer is repeated a few times
+ *     instead of ending a walk of thousands of pages.
+ *   - A resumable walk asks only for the samples beyond the edge an earlier
+ *     attempt reached.
+ *   - Inside a slice, a resumable walk stops on the slice's budget and on a
+ *     rate limit it cannot wait out, and reports itself truncated rather than
+ *     failing; a walk that is not resumable runs on under the job's limit.
+ */
+import { afterAll, beforeEach, describe, expect, it, vi } from "vitest";
+
+const { safeFetchMock } = vi.hoisted(() => ({ safeFetchMock: vi.fn() }));
+vi.mock("@/lib/safe-fetch", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("@/lib/safe-fetch")>();
+  return { ...actual, safeFetch: safeFetchMock };
+});
+vi.mock("@/lib/logging/context", () => ({
+  annotate: () => {},
+  getEvent: () => null,
+}));
+
+import { SafeFetchError } from "@/lib/safe-fetch";
+import {
+  GOOGLE_HEALTH_DATA_TYPES,
+  GOOGLE_HEALTH_TRANSIENT_RETRY,
+  forEachDataPointPage,
+  googleHealthSliceBudget,
+  runWithGoogleHealthClientOutcome,
+  runWithGoogleHealthStop,
+} from "../client";
+import { GoogleHealthApiError } from "../response-classifier";
+
+function page(n: number, next: boolean, status = 200, headers = {}): Response {
+  return new Response(
+    JSON.stringify(
+      status === 200
+        ? {
+            dataPoints: [{ n }],
+            ...(next ? { nextPageToken: String(n + 1) } : {}),
+          }
+        : { error: { code: status } },
+    ),
+    { status, headers: { "content-type": "application/json", ...headers } },
+  );
+}
+
+const baseDelay = GOOGLE_HEALTH_TRANSIENT_RETRY.baseDelayMs;
+beforeEach(() => {
+  safeFetchMock.mockReset();
+  GOOGLE_HEALTH_TRANSIENT_RETRY.baseDelayMs = 0;
+});
+afterAll(() => {
+  GOOGLE_HEALTH_TRANSIENT_RETRY.baseDelayMs = baseDelay;
+});
+
+const walk = (query: Parameters<typeof forEachDataPointPage>[3] = {}) =>
+  runWithGoogleHealthClientOutcome(() =>
+    forEachDataPointPage(
+      GOOGLE_HEALTH_DATA_TYPES.heartRate,
+      "token",
+      "fetchHeartRate",
+      query,
+      () => {},
+    ),
+  );
+
+describe("a server error or a lost request mid-walk", () => {
+  it("is repeated and the walk goes on", async () => {
+    safeFetchMock
+      .mockResolvedValueOnce(page(0, true))
+      .mockResolvedValueOnce(page(0, false, 503))
+      .mockRejectedValueOnce(new SafeFetchError("aborted", "timeout"))
+      .mockResolvedValueOnce(page(1, false));
+
+    const { outcome } = await walk();
+
+    expect(safeFetchMock).toHaveBeenCalledTimes(4);
+    expect(outcome).toMatchObject({ pages: 2, truncated: false });
+  });
+
+  it("fails the walk once the retries are spent", async () => {
+    safeFetchMock.mockResolvedValue(page(0, false, 500));
+    await expect(walk()).rejects.toBeInstanceOf(GoogleHealthApiError);
+    expect(safeFetchMock).toHaveBeenCalledTimes(
+      GOOGLE_HEALTH_TRANSIENT_RETRY.maxRetries + 1,
+    );
+  });
+
+  it("does not repeat an error that is not about the server", async () => {
+    safeFetchMock.mockRejectedValue(new TypeError("bad request init"));
+    await expect(walk()).rejects.toBeInstanceOf(TypeError);
+    expect(safeFetchMock).toHaveBeenCalledTimes(1);
+  });
+});
+
+describe("a resumable walk", () => {
+  it("asks only for the samples at or beyond the recorded edge", async () => {
+    safeFetchMock.mockResolvedValue(page(0, false));
+    await walk({
+      resumable: true,
+      edge: { at: new Date("2025-03-01T08:00:00Z"), order: "desc" },
+    });
+    const url = new URL(safeFetchMock.mock.calls[0]![0] as string);
+    expect(url.searchParams.get("filter")).toBe(
+      'heart_rate.sample_time.physical_time <= "2025-03-01T08:00:00.000Z"',
+    );
+  });
+
+  it("stops on the slice's page budget and reports itself truncated", async () => {
+    safeFetchMock.mockImplementation(async (url: string) =>
+      page(Number(new URL(url).searchParams.get("pageToken") ?? 0), true),
+    );
+    const budget = googleHealthSliceBudget(60_000, 3);
+    const { outcome } = await runWithGoogleHealthStop(
+      () => false,
+      () => walk({ resumable: true }),
+      budget,
+    );
+    expect(safeFetchMock).toHaveBeenCalledTimes(3);
+    expect(outcome.truncated).toBe(true);
+    expect(budget.stopReason).toBe("page_budget");
+  });
+
+  it("starts the slice's clock at the first walk, not when the slice was set up", async () => {
+    safeFetchMock.mockResolvedValue(page(0, false));
+    let clock = 0;
+    const budget = googleHealthSliceBudget(1_000, 500, () => clock);
+    // The slice waited ten minutes for the account's lock before walking.
+    clock = 600_000;
+    const { outcome } = await runWithGoogleHealthStop(
+      () => false,
+      () => walk({ resumable: true }),
+      budget,
+    );
+    expect(outcome).toMatchObject({ pages: 1, truncated: false });
+    expect(budget.deadline).toBe(601_000);
+  });
+
+  it("ends the slice on a rate limit it cannot wait out, without failing", async () => {
+    safeFetchMock
+      .mockResolvedValueOnce(page(0, true))
+      .mockResolvedValueOnce(page(1, true, 429, { "retry-after": "3600" }));
+    const budget = googleHealthSliceBudget(60_000, 500);
+    const { outcome } = await runWithGoogleHealthStop(
+      () => false,
+      () => walk({ resumable: true }),
+      budget,
+    );
+    expect(outcome).toMatchObject({ pages: 1, truncated: true });
+    expect(budget.stopReason).toBe("rate_limited");
+  });
+
+  it("still fails on a rate limit outside a slice", async () => {
+    safeFetchMock.mockResolvedValue(
+      page(0, true, 429, { "retry-after": "3600" }),
+    );
+    await expect(walk({ resumable: true })).rejects.toBeInstanceOf(
+      GoogleHealthApiError,
+    );
+  });
+});
+
+describe("a walk that is not resumable", () => {
+  it("runs past the slice's budget to its end", async () => {
+    safeFetchMock.mockImplementation(async (url: string) => {
+      const n = Number(new URL(url).searchParams.get("pageToken") ?? 0);
+      return page(n, n < 5);
+    });
+    const budget = googleHealthSliceBudget(0, 1);
+    const { outcome } = await runWithGoogleHealthStop(
+      () => false,
+      () => walk(),
+      budget,
+    );
+    expect(safeFetchMock).toHaveBeenCalledTimes(6);
+    expect(outcome.truncated).toBe(false);
+  });
+
+  it("still stops on the job's own budget", async () => {
+    safeFetchMock.mockImplementation(async () => page(0, true));
+    let asked = 0;
+    const { outcome } = await runWithGoogleHealthStop(
+      () => ++asked > 2,
+      () => walk(),
+      googleHealthSliceBudget(60_000, 500),
+    );
+    expect(safeFetchMock).toHaveBeenCalledTimes(2);
+    expect(outcome.truncated).toBe(true);
+  });
+});
diff --git a/src/lib/google-health/client.ts b/src/lib/google-health/client.ts
index 3bdab3aec..1bcdee440 100644
--- a/src/lib/google-health/client.ts
+++ b/src/lib/google-health/client.ts
@@ -36,7 +36,7 @@
 import { AsyncLocalStorage } from "node:async_hooks";
 import { createHash, randomBytes } from "node:crypto";
 import { annotate, getEvent } from "@/lib/logging/context";
-import { safeFetch } from "@/lib/safe-fetch";
+import { SafeFetchError, safeFetch } from "@/lib/safe-fetch";
 import { wallClockInTz } from "@/lib/tz/wall-clock";
 import {
   GoogleHealthApiError,
@@ -134,18 +134,140 @@ export async function runWithGoogleHealthClientOutcome<T>(
  * reaching the page ceiling: the resource is incomplete, the cycle is not
  * stamped, and the reason shown is that only part of the history was
  * processed. Outside such a scope the walks never stop early.
+ *
+ * A backfill slice adds a second, tighter limit (`GoogleHealthSliceBudget`):
+ * minutes and pages rather than the job's hours. Only a walk that keeps its
+ * place across attempts (`resumable`) honours it, because only such a walk
+ * loses nothing by stopping; a walk that would start over from its first page
+ * runs on to the end under the job's limit alone.
  */
-const stopStorage = new AsyncLocalStorage<() => boolean>();
+interface GoogleHealthWalkLimits {
+  shouldStop: () => boolean;
+  slice?: GoogleHealthSliceBudget;
+}
 
-function stopRequested(): boolean {
-  return stopStorage.getStore()?.() === true;
+/** Why a backfill slice stopped walking. */
+export type GoogleHealthSliceStopReason =
+  "time_budget" | "page_budget" | "rate_limited" | "job_budget";
+
+/**
+ * One backfill slice's share of the work: a span of wall-clock time and a
+ * page count, both well inside the job's own expiry. The clock starts the
+ * first time a walk asks, which is after the slice has the account's lock: a
+ * slice that waited for an hourly sync to finish does not start out with its
+ * time already spent. `pages` counts every page the slice's walks have read;
+ * `stopReason` is set the first time a limit is reached and stays set, so
+ * every walk after it stops too.
+ */
+export interface GoogleHealthSliceBudget {
+  ms: number;
+  /** When the slice's time is up; null until the first walk asks. */
+  deadline: number | null;
+  maxPages: number;
+  pages: number;
+  stopReason: GoogleHealthSliceStopReason | null;
+  now: () => number;
+}
+
+/** A fresh slice budget of `ms` milliseconds and `maxPages` pages. */
+export function googleHealthSliceBudget(
+  ms: number,
+  maxPages: number,
+  now: () => number = Date.now,
+): GoogleHealthSliceBudget {
+  return {
+    ms,
+    deadline: null,
+    maxPages,
+    pages: 0,
+    stopReason: null,
+    now,
+  };
+}
+
+const stopStorage = new AsyncLocalStorage<GoogleHealthWalkLimits>();
+
+/** Whether the slice in scope has used its budget (and why, once it has). */
+function sliceExhausted(slice: GoogleHealthSliceBudget): boolean {
+  if (slice.stopReason) return true;
+  slice.deadline ??= slice.now() + slice.ms;
+  if (slice.now() >= slice.deadline) slice.stopReason = "time_budget";
+  else if (slice.pages >= slice.maxPages) slice.stopReason = "page_budget";
+  return slice.stopReason !== null;
+}
+
+/**
+ * Whether a walk should stop before its next request. Every walk stops on the
+ * job's limit; a resumable one also stops on the slice's.
+ */
+function stopRequested(resumable = false): boolean {
+  const limits = stopStorage.getStore();
+  if (!limits) return false;
+  if (limits.shouldStop()) {
+    if (limits.slice && !limits.slice.stopReason) {
+      limits.slice.stopReason = "job_budget";
+    }
+    return true;
+  }
+  return (
+    resumable && limits.slice !== undefined && sliceExhausted(limits.slice)
+  );
+}
+
+/**
+ * Whether the backfill slice in scope has used its budget. A collection that
+ * has not started yet waits for the next slice rather than starting now.
+ * False outside a slice.
+ */
+export function googleHealthSliceExhausted(): boolean {
+  const limits = stopStorage.getStore();
+  if (!limits) return false;
+  if (limits.shouldStop()) {
+    if (limits.slice && !limits.slice.stopReason) {
+      limits.slice.stopReason = "job_budget";
+    }
+    return true;
+  }
+  return limits.slice !== undefined && sliceExhausted(limits.slice);
+}
+
+/** Pages the slice in scope has read so far (0 outside a slice). */
+export function googleHealthSlicePagesRead(): number {
+  return stopStorage.getStore()?.slice?.pages ?? 0;
+}
+
+/** Count one page read against the slice in scope, if any. */
+function noteSlicePage(): void {
+  const slice = stopStorage.getStore()?.slice;
+  if (slice) slice.pages += 1;
+}
+
+/** End the slice in scope for `reason` (no-op outside a slice). */
+function endSlice(reason: GoogleHealthSliceStopReason): void {
+  const slice = stopStorage.getStore()?.slice;
+  if (slice && !slice.stopReason) slice.stopReason = reason;
+}
+
+/** Whether a resumable walk can stop and keep its place here. */
+function inSlice(): boolean {
+  return stopStorage.getStore()?.slice !== undefined;
 }
 
 export async function runWithGoogleHealthStop<T>(
   shouldStop: () => boolean,
   fn: () => Promise<T>,
+  slice?: GoogleHealthSliceBudget,
 ): Promise<T> {
-  return stopStorage.run(shouldStop, fn);
+  return stopStorage.run({ shouldStop, slice }, fn);
+}
+
+/**
+ * Mark the resource in scope truncated without a walk: a collection a slice
+ * left for the next one. The cycle then reports itself incomplete, so the
+ * backfill does not mistake a skipped collection for an empty one.
+ */
+export function noteGoogleHealthDeferred(): void {
+  notePagination(0, 0, true);
 }
 
 export const GOOGLE_HEALTH_API_BASE = "https://health.googleapis.com/v4";
@@ -527,6 +649,7 @@ export function resolveGoogleHealthUserId(
 //     camelCase nested objects (`sampleTime.physicalTime`,
 //     `interval.startTime`, `civilStartTime.date`).
 //
+
 // proto3 int64 fields arrive as JSON **strings** (`"12345"`) — every numeric
 // extractor coerces numeric strings before the finite check.
 
@@ -553,6 +676,9 @@ export const GOOGLE_HEALTH_ACTIVITY_PAGE_SIZE = 25;
  */
 export const GOOGLE_HEALTH_DENSE_MAX_PAGES = 10_000;
 
+/** Page ceiling for every other list walk. */
+export const GOOGLE_HEALTH_DEFAULT_MAX_PAGES = 1000;
+
 /** `dataPoints.list` envelope: `{ dataPoints, nextPageToken }`. */
 interface GoogleHealthDataPointPage {
   dataPoints?: GoogleHealthDataPoint[];
@@ -578,6 +704,20 @@ interface DataPointQuery {
    * surfaces it so a live account reports which grammar Google accepted.
    */
   onDateFilterStyle?: (style: GoogleHealthDateFilterStyle) => void;
+  /**
+   * The walk keeps its place across attempts (a backfill's resume cursor), so
+   * it may stop on the backfill slice's budget and on a rate limit it cannot
+   * wait out, and report itself truncated instead of failing: the next slice
+   * picks up from the edge it recorded.
+   */
+  resumable?: boolean;
+  /**
+   * Where an earlier attempt of this walk got to: the oldest sample it wrote
+   * when the walk ran newest first (`desc`), the newest when it ran oldest
+   * first (`asc`). The walk asks only for the samples at or beyond it; the
+   * one sample on the edge itself is read again and overwrites in place.
+   */
+  edge?: { at: Date; order: "desc" | "asc" };
 }
 
 const pad2 = (n: number): string => String(n).padStart(2, "0");
@@ -797,6 +937,21 @@ export function googleHealthRetryDelayMs(
   return undefined;
 }
 
+/**
+ * How a data request rides out a server that did not answer properly: a
+ * 500, 502, 503 or 504, a timeout, or a broken connection. A short history
+ * reads a handful of pages and rarely meets one; a full-history heart-rate
+ * walk reads thousands, and a single one used to end the walk and throw away
+ * everything it had read. Three tries more, 2, 4 and 8 s apart (or the
+ * `Retry-After` a 503 names, up to a minute), before the request fails.
+ */
+export const GOOGLE_HEALTH_TRANSIENT_RETRY = {
+  maxRetries: 3,
+  baseDelayMs: 2_000,
+};
+
+const GOOGLE_HEALTH_TRANSIENT_STATUSES = new Set([500, 502, 503, 504]);
+
 function waitMs(ms: number): Promise<void> {
   return new Promise((resolve) => setTimeout(resolve, ms));
 }
@@ -811,10 +966,12 @@ interface GoogleHealthDataResponse<T> {
 /**
  * Send one data request and answer with the response it finally got.
  *
- * Two answers are handled here rather than handed back:
+ * Three answers are handled here rather than handed back:
  *   - 429: the request waits (see `GOOGLE_HEALTH_RATE_LIMIT`) and is sent
  *     again, up to `maxRetries` times, unless the caller's stop condition
  *     says to end the walk.
+ *   - a server error or no answer at all (see
+ *     `GOOGLE_HEALTH_TRANSIENT_RETRY`): the same, with its own count.
  *   - 401 with a token source: the token expired or was revoked between
  *     the source's last check and this request. The source is asked once for
  *     a fresh token and the request is repeated. A second 401, or a 401 on a
@@ -830,6 +987,7 @@ async function googleHealthDataRequest<T>(
   isExpectedFallback: (status: number) => boolean = () => false,
 ): Promise<GoogleHealthDataResponse<T>> {
   let rateLimited = 0;
+  let transient = 0;
   let refreshed = false;
   let forceRefresh = false;
   for (;;) {
@@ -837,7 +995,33 @@ async function googleHealthDataRequest<T>(
       typeof token === "string" ? token : await token({ forceRefresh });
     forceRefresh = false;
     const started = performance.now();
-    const res = await send(accessToken);
+    let res: Response;
+    try {
+      res = await send(accessToken);
+    } catch (err) {
+      // No answer at all: the request timed out or the connection broke.
+      // On a walk of a thousand pages one of those is a matter of time, and
+      // it cost the whole walk.
+      const retry =
+        err instanceof SafeFetchError &&
+        (err.kind === "timeout" || err.kind === "network") &&
+        transient < GOOGLE_HEALTH_TRANSIENT_RETRY.maxRetries &&
+        !stopRequested();
+      const delayMs =
+        GOOGLE_HEALTH_TRANSIENT_RETRY.baseDelayMs * 2 ** transient;
+      getEvent()?.addExternalCall({
+        service: "google-health",
+        method: label,
+        duration_ms: Math.round(performance.now() - started),
+        ...(retry
+          ? { note: `no_response_retrying_in_ms=${delayMs}` }
+          : { error: err instanceof Error ? err.message : String(err) }),
+      });
+      if (!retry) throw err;
+      transient += 1;
+      await waitMs(delayMs);
+      continue;
+    }
     const json = (await res.json().catch(() => null)) as T | null;
     const verdict = classifyGoogleHealthResponse(res.status);
     const apiErrorDetail =
@@ -859,6 +1043,17 @@ async function googleHealthDataRequest<T>(
       !stopRequested();
     const willRefresh =
       res.status === 401 && typeof token !== "string" && !refreshed;
+    const transientDelayMs = GOOGLE_HEALTH_TRANSIENT_STATUSES.has(res.status)
+      ? Math.min(
+          googleHealthRetryDelayMs(res, json) ??
+            GOOGLE_HEALTH_TRANSIENT_RETRY.baseDelayMs * 2 ** transient,
+          GOOGLE_HEALTH_RATE_LIMIT.maxDelayMs,
+        )
+      : 0;
+    const willRetryTransient =
+      GOOGLE_HEALTH_TRANSIENT_STATUSES.has(res.status) &&
+      transient < GOOGLE_HEALTH_TRANSIENT_RETRY.maxRetries &&
+      !stopRequested();
 
     getEvent()?.addExternalCall({
       service: "google-health",
@@ -871,14 +1066,16 @@ async function googleHealthDataRequest<T>(
           ? { note: `rate_limited_retrying_in_ms=${backoffMs}` }
           : willRefresh
             ? { note: "token_rejected_retrying_with_fresh_token" }
-            : {
-                error:
-                  verdict.classification === "success"
-                    ? undefined
-                    : apiErrorDetail
-                      ? `${verdict.reason} ${apiErrorDetail}`
-                      : verdict.reason,
-              }),
+            : willRetryTransient
+              ? { note: `server_error_retrying_in_ms=${transientDelayMs}` }
+              : {
+                  error:
+                    verdict.classification === "success"
+                      ? undefined
+                      : apiErrorDetail
+                        ? `${verdict.reason} ${apiErrorDetail}`
+                        : verdict.reason,
+                }),
     });
 
     if (willWait) {
@@ -886,6 +1083,11 @@ async function googleHealthDataRequest<T>(
       await waitMs(backoffMs);
       continue;
     }
+    if (willRetryTransient) {
+      transient += 1;
+      await waitMs(transientDelayMs);
+      continue;
+    }
     if (willRefresh) {
       refreshed = true;
       forceRefresh = true;
@@ -947,8 +1149,9 @@ export async function forEachDataPointPage(
   query: DataPointQuery,
   onPage: (points: GoogleHealthDataPoint[]) => void | Promise<void>,
 ): Promise<void> {
-  const maxPages = query.maxPages ?? 1000;
+  const maxPages = query.maxPages ?? GOOGLE_HEALTH_DEFAULT_MAX_PAGES;
   const pageSize = query.pageSize ?? GOOGLE_HEALTH_PAGE_SIZE;
+  const resumable = query.resumable === true;
 
   let requestCount = 0;
 
@@ -961,11 +1164,12 @@ export async function forEachDataPointPage(
     let stopped = false;
 
     do {
-      if (stopRequested()) {
+      if (stopRequested(resumable)) {
         stopped = true;
         break;
       }
       const params = new URLSearchParams({ pageSize: String(pageSize) });
+      const filters: string[] = [];
       if (query.start) {
         const { field, bound } = incrementalFilter(
           dataType,
@@ -973,8 +1177,20 @@ export async function forEachDataPointPage(
           query.tz,
           dateStyle,
         );
-        params.set("filter", `${field} >= "${bound}"`);
+        filters.push(`${field} >= "${bound}"`);
       }
+      if (query.edge) {
+        const { field, bound } = incrementalFilter(
+          dataType,
+          query.edge.at,
+          query.tz,
+          dateStyle,
+        );
+        filters.push(
+          `${field} ${query.edge.order === "desc" ? "<=" : ">="} "${bound}"`,
+        );
+      }
+      if (filters.length > 0) params.set("filter", filters.join(" AND "));
       if (pageToken) params.set("pageToken", pageToken);
 
       requestCount += 1;
@@ -985,7 +1201,7 @@ export async function forEachDataPointPage(
       // an error next to the 200 that followed it. It is recorded as a note
       // now; any other 400 still carries its error.
       const firstRequest = requestCount === 1;
-      const { json, verdict, apiErrorDetail } =
+      const { status, json, verdict, apiErrorDetail } =
         await googleHealthDataRequest<GoogleHealthDataPointPage>(
           accessToken,
           `${verb}(page=${pageCount})`,
@@ -1003,6 +1219,15 @@ export async function forEachDataPointPage(
             firstRequest &&
             status === 400,
         );
+      // A rate limit the request could not wait out ends a resumable walk
+      // inside a backfill slice where it is: the pages before it are written
+      // and their edge recorded, so this is a pause, not a failure. The slice
+      // ends with it, since every other walk would meet the same quota.
+      if (status === 429 && resumable && inSlice()) {
+        endSlice("rate_limited");
+        stopped = true;
+        break;
+      }
       if (verdict.classification !== "success") {
         throw new GoogleHealthApiError({
           verb,
@@ -1017,6 +1242,7 @@ export async function forEachDataPointPage(
       pageToken = json?.nextPageToken ?? null;
       pageCount += 1;
       fetched += page.length;
+      noteSlicePage();
       await onPage(page);
     } while (pageToken && pageCount < maxPages);
 
@@ -1245,7 +1471,7 @@ export async function fetchDailyRollUp(
     let totalPages = 0;
     let truncated = false;
     for (const chunk of chunkCivilRange(startCivil, endCivil, maxDays)) {
-      if (stopRequested()) {
+      if (stopRequested(false)) {
         truncated = true;
         break;
       }
@@ -1295,6 +1521,7 @@ export async function fetchDailyRollUp(
         for (const p of json?.rollupDataPoints ?? []) points.push(p);
         pageToken = json?.nextPageToken ?? null;
         pageCount += 1;
+        noteSlicePage();
       } while (pageToken && pageCount < 100);
       totalPages += pageCount;
       truncated ||= Boolean(pageToken);
diff --git a/src/lib/google-health/mappers.ts b/src/lib/google-health/mappers.ts
index d73666dc6..194a782ff 100644
--- a/src/lib/google-health/mappers.ts
+++ b/src/lib/google-health/mappers.ts
@@ -387,6 +387,21 @@ function resolveMeasuredAt(
   return fallback;
 }
 
+/**
+ * The sample instant of a spot-reading `DataPoint` (`sample` data types), or
+ * null for any other shape or a point without a parseable time. A backfill
+ * reads it to record how far a walk has got.
+ */
+export function googleHealthSampleInstant(
+  point: GoogleHealthDataPoint,
+  dataType: GoogleHealthDataType,
+  tz?: string,
+): Date | null {
+  if (dataType.timeField !== "sample") return null;
+  const t = readPath(point, `${dataType.key}.sampleTime.physicalTime`);
+  return typeof t === "string" ? parseLocalInstant(t, tz) : null;
+}
+
 /**
  * Stable anchor for a `DataPoint`'s externalId. A spot reading anchors on its
  * sample time; a daily summary on its civil date. Combined with a type-specific
diff --git a/src/lib/google-health/sync-core.ts b/src/lib/google-health/sync-core.ts
index dc215266d..80004abf5 100644
--- a/src/lib/google-health/sync-core.ts
+++ b/src/lib/google-health/sync-core.ts
@@ -37,6 +37,9 @@ import {
 import { invalidateStatusInsightsForTypes } from "@/lib/insights/comprehensive-generate";
 import {
   googleHealthOutcomeTruncated,
+  googleHealthSliceExhausted,
+  googleHealthSlicePagesRead,
+  noteGoogleHealthDeferred,
   noteGoogleHealthMapped,
   noteGoogleHealthOutcomeFailure,
   noteGoogleHealthWritten,
@@ -402,33 +405,75 @@ export async function runWithGoogleHealthSyncCycle<T>(
 }
 
 /**
- * Collections a full-history backfill already walked to the end, carried from
- * one attempt of the backfill to the next.
+ * How far a full-history backfill has got, carried from one attempt of the
+ * backfill to the next.
  *
- * A backfill that ended early (its job budget ran out, a collection failed)
- * used to start the next attempt from the first page of the first collection,
- * so the dense heart-rate walk, thousands of pages, was paid for again on
- * every retry, and an account whose walk never fit into one attempt never
- * finished at all. Each collection that completes cleanly is now written to
- * `backfillProgress`, and the next attempt skips it and goes on with the
- * collections it did not reach. A collection is the unit because Google
- * offers no cursor that survives between attempts; its page tokens are not
- * documented to outlive the walk that received them.
+ * Two grains. A collection walked to the end is noted in `done`, and the next
+ * attempt skips it. A collection read page by page (the spot readings: heart
+ * rate, weight, glucose, ...) also notes, after every page it writes, the
+ * edge it has reached: the oldest sample written so far when the walk runs
+ * newest first, as Google's list does. The next attempt asks Google only for
+ * the samples at or beyond that edge, so a collection that does not fit into
+ * one attempt is worked through over several instead of being read from its
+ * first page every time.
+ *
+ * The edge is a sample time, not Google's page token: page tokens are not
+ * documented to outlive the walk that received them, a sample time is a
+ * filter Google documents. The one sample on the edge itself is read twice
+ * and overwrites its own row.
+ *
+ * Before the edge existed only `done` was kept, and a heart-rate history of
+ * years that one attempt could not finish (its budget, a rate limit, one
+ * failed page among thousands) started again from the newest page on every
+ * attempt and never reached the end (#1220).
  */
+export interface GoogleHealthBackfillCursor {
+  /** The edge: the sample instant (ISO 8601) the walk has written up to. */
+  at: string;
+  /** The order the walk returned samples in: newest first, or oldest first. */
+  order: "desc" | "asc";
+  /** Pages this collection has read across every attempt so far. */
+  pages: number;
+}
+
+/** What one collection came to in one backfill attempt. */
+export interface GoogleHealthBackfillCollectionReport {
+  key: string;
+  /**
+   * `done`: walked to the end. `stopped`: ended short on a budget, a page
+   * ceiling or a rate limit, with nothing failed. `deferred`: not started,
+   * left for the next slice. `failed`: a request or a write failed, or the
+   * collection answered 403.
+   */
+  status: "done" | "stopped" | "deferred" | "failed";
+  pages: number;
+  durationMs: number;
+  /** The edge before and after this attempt, for a resumable collection. */
+  edgeFrom?: string | null;
+  edgeTo?: string | null;
+}
+
 interface BackfillResumeTracker {
   userId: string;
   done: Set<string>;
+  cursors: Map<string, GoogleHealthBackfillCursor>;
   /** Collections this attempt skipped because an earlier one finished them. */
   skipped: string[];
+  /** Collections whose edge this attempt moved, with the edge they started from. */
+  advanced: Map<string, string | null>;
+  collections: GoogleHealthBackfillCollectionReport[];
 }
 const backfillResumeStorage = new AsyncLocalStorage<BackfillResumeTracker>();
 
+function progressRecord(value: unknown): Record<string, unknown> {
+  return value && typeof value === "object" && !Array.isArray(value)
+    ? (value as Record<string, unknown>)
+    : {};
+}
+
 /** Read the `backfillProgress` column into the set of finished collections. */
 export function readGoogleHealthBackfillDone(value: unknown): Set<string> {
-  const done =
-    value && typeof value === "object" && !Array.isArray(value)
-      ? (value as { done?: unknown }).done
-      : undefined;
+  const done = progressRecord(value).done;
   return new Set(
     Array.isArray(done)
       ? done.filter(
@@ -438,20 +483,188 @@ export function readGoogleHealthBackfillDone(value: unknown): Set<string> {
   );
 }
 
+/** Read the `backfillProgress` column into the per-collection edges. */
+export function readGoogleHealthBackfillCursors(
+  value: unknown,
+): Map<string, GoogleHealthBackfillCursor> {
+  const out = new Map<string, GoogleHealthBackfillCursor>();
+  const cursors = progressRecord(progressRecord(value).cursors);
+  for (const [key, raw] of Object.entries(cursors)) {
+    if (key.length > 64) continue;
+    const c = progressRecord(raw);
+    const at = typeof c.at === "string" ? c.at : null;
+    if (!at || Number.isNaN(Date.parse(at))) continue;
+    out.set(key, {
+      at: new Date(at).toISOString(),
+      order: c.order === "asc" ? "asc" : "desc",
+      pages:
+        typeof c.pages === "number" && Number.isFinite(c.pages) && c.pages > 0
+          ? Math.trunc(c.pages)
+          : 0,
+    });
+  }
+  return out;
+}
+
+/**
+ * Write the tracker's progress with one change applied, and apply it to the
+ * tracker only once the write has landed: progress that is not on disk is
+ * progress the next attempt cannot see, so it must not count in this one.
+ */
+async function persistBackfillProgress(
+  tracker: BackfillResumeTracker,
+  next: {
+    done: Set<string>;
+    cursors: Map<string, GoogleHealthBackfillCursor>;
+  },
+): Promise<void> {
+  await prisma.googleHealthConnection.update({
+    where: { userId: tracker.userId },
+    data: {
+      backfillProgress: {
+        done: [...next.done],
+        cursors: Object.fromEntries(
+          [...next.cursors].map(([key, c]) => [
+            key,
+            { at: c.at, order: c.order, pages: c.pages },
+          ]),
+        ),
+      },
+    },
+  });
+  // `next` may be the tracker's own collections: copy before clearing.
+  const done = [...next.done];
+  const cursors = [...next.cursors];
+  tracker.done.clear();
+  for (const key of done) tracker.done.add(key);
+  tracker.cursors.clear();
+  for (const [key, c] of cursors) tracker.cursors.set(key, c);
+}
+
+/** What one backfill attempt did, as `runWithGoogleHealthBackfillResume` reports it. */
+export interface GoogleHealthBackfillAttempt<T> {
+  result: T;
+  skipped: string[];
+  /** Collections whose edge moved, each with the edge it started from. */
+  advanced: Map<string, string | null>;
+  collections: GoogleHealthBackfillCollectionReport[];
+}
+
 /**
  * Run a full-history backfill attempt that resumes: collections in `done` are
- * skipped, and each collection finished cleanly during this attempt is added
- * to it and persisted at once, so an attempt that dies part-way keeps what it
- * finished.
+ * skipped, a collection with an edge in `cursors` starts from it, and each
+ * collection finished or page written during this attempt is persisted at
+ * once, so an attempt that dies part-way keeps what it did.
  */
 export async function runWithGoogleHealthBackfillResume<T>(
   userId: string,
   done: Set<string>,
   fn: () => Promise<T>,
-): Promise<{ result: T; skipped: string[] }> {
-  const tracker: BackfillResumeTracker = { userId, done, skipped: [] };
+  cursors: Map<string, GoogleHealthBackfillCursor> = new Map(),
+): Promise<GoogleHealthBackfillAttempt<T>> {
+  const tracker: BackfillResumeTracker = {
+    userId,
+    done,
+    cursors,
+    skipped: [],
+    advanced: new Map(),
+    collections: [],
+  };
   const result = await backfillResumeStorage.run(tracker, fn);
-  return { result, skipped: tracker.skipped };
+  return {
+    result,
+    skipped: tracker.skipped,
+    advanced: tracker.advanced,
+    collections: tracker.collections,
+  };
+}
+
+/**
+ * Where a resumable collection's walk starts in this backfill attempt: the
+ * edge an earlier attempt recorded (if any) and the pages it has already
+ * read. Null outside a backfill, where every walk reads its whole window.
+ */
+export function googleHealthBackfillCursor(key: GoogleHealthCollectionKey): {
+  edge?: { at: Date; order: "desc" | "asc" };
+  pagesSoFar: number;
+} | null {
+  const resume = backfillResumeStorage.getStore();
+  if (!resume) return null;
+  const cursor = resume.cursors.get(key);
+  return cursor
+    ? {
+        edge: { at: new Date(cursor.at), order: cursor.order },
+        pagesSoFar: cursor.pages,
+      }
+    : { pagesSoFar: 0 };
+}
+
+/**
+ * Record that a resumable collection wrote one more page, holding samples
+ * from `first` to `last` in the order Google returned them. Moves the
+ * collection's edge to the far end of the page and persists it. Outside a
+ * backfill this does nothing.
+ *
+ * The order is read off the first page whose two ends differ and kept for
+ * the rest of the backfill; Google returns its lists newest first, which is
+ * also what a page that cannot tell is taken to mean.
+ */
+export async function recordGoogleHealthBackfillPage(
+  key: GoogleHealthCollectionKey,
+  page: { first: Date | null; last: Date | null },
+): Promise<void> {
+  const resume = backfillResumeStorage.getStore();
+  if (!resume) return;
+  const current = resume.cursors.get(key);
+  const order: "desc" | "asc" =
+    current?.order ??
+    (page.first && page.last && page.first.getTime() < page.last.getTime()
+      ? "asc"
+      : "desc");
+  const ends = [page.first, page.last].filter((d): d is Date => d !== null);
+  const far =
+    ends.length === 0
+      ? null
+      : new Date(
+          order === "desc"
+            ? Math.min(...ends.map((d) => d.getTime()))
+            : Math.max(...ends.map((d) => d.getTime())),
+        );
+  const currentAt = current ? Date.parse(current.at) : null;
+  const moved =
+    far !== null &&
+    (currentAt === null ||
+      (order === "desc"
+        ? far.getTime() < currentAt
+        : far.getTime() > currentAt));
+  if (!current && !moved) return;
+  const nextCursor: GoogleHealthBackfillCursor = {
+    at: moved ? far.toISOString() : current!.at,
+    order,
+    pages: (current?.pages ?? 0) + 1,
+  };
+  const cursors = new Map(resume.cursors);
+  cursors.set(key, nextCursor);
+  try {
+    await persistBackfillProgress(resume, { done: resume.done, cursors });
+    if (moved && !resume.advanced.has(key)) {
+      resume.advanced.set(key, current?.at ?? null);
+    }
+  } catch (err) {
+    // The page's rows are written; only the note of how far the walk got is
+    // missing, so the next attempt reads this page again. Not a failure.
+    getEvent()?.addWarning(
+      `google-health: backfill progress write failed for ${key}: ${err}`,
+    );
+    annotate({
+      meta: { "googleHealth.backfill.progressWriteFailed": key },
+    });
+  }
+}
+
+/** Hard failures the cycle in scope has recorded so far. */
+export function googleHealthHardFailureCount(): number {
+  return hardFailStorage.getStore()?.failures.length ?? 0;
 }
 
 /**
@@ -459,10 +672,12 @@ export async function runWithGoogleHealthBackfillResume<T>(
  * one in scope. Outside a backfill this is just `fn()`.
  *
  * Inside one, a collection already walked to the end by an earlier attempt is
- * skipped. Otherwise it runs, and it counts as finished only when nothing
- * went wrong while it ran: no hard failure on the cycle's ledger, no 403
- * soft-skip, and no walk that ended short (its page ceiling, or the job's
- * budget asking it to stop). Anything less is walked again next attempt.
+ * skipped, and so is one the slice has no budget left to start: it is left
+ * for the next slice, and the cycle reports itself incomplete. Otherwise it
+ * runs, and it counts as finished only when nothing went wrong while it ran:
+ * no hard failure on the cycle's ledger, no 403 soft-skip, and no walk that
+ * ended short (its page ceiling, or a budget asking it to stop). Anything
+ * less is walked again next attempt, from its edge when it has one.
  */
 export async function runGoogleHealthCollection(
   key: GoogleHealthCollectionKey,
@@ -474,15 +689,29 @@ export async function runGoogleHealthCollection(
     resume.skipped.push(key);
     return 0;
   }
+  if (googleHealthSliceExhausted()) {
+    noteGoogleHealthDeferred();
+    resume.collections.push({
+      key,
+      status: "deferred",
+      pages: 0,
+      durationMs: 0,
+    });
+    return 0;
+  }
+  const startedAt = performance.now();
+  const pagesBefore = googleHealthSlicePagesRead();
+  const edgeFrom = resume.cursors.get(key)?.at ?? null;
   const hardBefore = hardFailStorage.getStore()?.failures.length ?? 0;
   const softBefore = softSkipStorage.getStore()?.count ?? 0;
   const truncatedBefore = googleHealthOutcomeTruncated();
   const imported = await fn();
-  const clean =
-    (hardFailStorage.getStore()?.failures.length ?? 0) === hardBefore &&
-    (softSkipStorage.getStore()?.count ?? 0) === softBefore &&
-    !truncatedBefore &&
-    !googleHealthOutcomeTruncated();
+  const failedHard =
+    (hardFailStorage.getStore()?.failures.length ?? 0) !== hardBefore ||
+    (softSkipStorage.getStore()?.count ?? 0) !== softBefore;
+  const truncated = truncatedBefore || googleHealthOutcomeTruncated();
+  const clean = !failedHard && !truncated;
+  let finished = false;
   if (clean) {
     // The collection counts as finished only once the note says so. The job
     // reads the size of `done` as this attempt's progress and sends another
@@ -490,11 +719,13 @@ export async function runGoogleHealthCollection(
     // progress nobody can see next attempt, and a chain of slices could keep
     // "progressing" over the same collection forever.
     try {
-      await prisma.googleHealthConnection.update({
-        where: { userId: resume.userId },
-        data: { backfillProgress: { done: [...resume.done, key] } },
+      const cursors = new Map(resume.cursors);
+      cursors.delete(key);
+      await persistBackfillProgress(resume, {
+        done: new Set([...resume.done, key]),
+        cursors,
       });
-      resume.done.add(key);
+      finished = true;
     } catch (err) {
       // Not finished, then: the collection is walked again next attempt. It
       // must not fail a collection whose rows are written.
@@ -506,6 +737,14 @@ export async function runGoogleHealthCollection(
       });
     }
   }
+  const edgeTo = finished ? null : (resume.cursors.get(key)?.at ?? null);
+  resume.collections.push({
+    key,
+    status: finished ? "done" : failedHard ? "failed" : "stopped",
+    pages: googleHealthSlicePagesRead() - pagesBefore,
+    durationMs: Math.round(performance.now() - startedAt),
+    ...(edgeFrom !== null || edgeTo !== null ? { edgeFrom, edgeTo } : {}),
+  });
   return imported;
 }
 
diff --git a/src/lib/google-health/sync-lock.ts b/src/lib/google-health/sync-lock.ts
index db8ca51c8..ddb16523d 100644
--- a/src/lib/google-health/sync-lock.ts
+++ b/src/lib/google-health/sync-lock.ts
@@ -16,7 +16,9 @@
  * the hourly poll skips the account for this tick, the manual trigger answers
  * that a sync is already running, and the backfill and the repair wait a
  * bounded time for a short run to finish before handing their job back to
- * pg-boss to retry.
+ * pg-boss to retry. The hourly poll waits too, for about one backfill slice:
+ * a backfill lets go of the account between its slices, so the hourly sync
+ * gets its turn instead of being skipped for as long as the import runs.
  */
 import { withJobLock, type GuardedRun } from "@/lib/jobs/job-lock";
 
@@ -32,6 +34,16 @@ export function googleHealthSyncLockKey(userId: string): string {
  */
 export const GOOGLE_HEALTH_SYNC_LOCK_WAIT_MS = 10 * 60 * 1000;
 
+/**
+ * How long the hourly poll waits for an account another run holds. A backfill
+ * slice walks for five minutes and then lets go
+ * (`GOOGLE_HEALTH_BACKFILL_SLICE_MS`); the page in flight, a rate-limit wait
+ * and the slice's own bookkeeping can add a minute or two, and the next slice
+ * starts a minute after this one ends. Eight minutes covers that, and leaves
+ * the hourly job well inside its fifteen-minute expiry.
+ */
+export const GOOGLE_HEALTH_POLL_LOCK_WAIT_MS = 8 * 60 * 1000;
+
 /**
  * Run `run` while holding the account's Google Health lock. Resolves
  * `{ ran: false }` without calling `run` when another run holds it and does
diff --git a/src/lib/google-health/sync-metrics.ts b/src/lib/google-health/sync-metrics.ts
index a86dfb59e..2bcad8002 100644
--- a/src/lib/google-health/sync-metrics.ts
+++ b/src/lib/google-health/sync-metrics.ts
@@ -27,12 +27,14 @@
  */
 import {
   GOOGLE_HEALTH_DATA_TYPES,
+  GOOGLE_HEALTH_DEFAULT_MAX_PAGES,
   GOOGLE_HEALTH_DENSE_MAX_PAGES,
   type GoogleHealthDataType,
   type GoogleHealthMappedMeasurement,
   type GoogleHealthTokenSource,
   fetchDataPoints,
   forEachDataPointPage,
+  googleHealthSampleInstant,
   mapBloodGlucose,
   mapBodyFat,
   mapCoreBodyTemperature,
@@ -44,11 +46,15 @@ import {
   mapRestingHeartRate,
   mapWeight,
   mapWristTemperature,
+  noteGoogleHealthDeferred,
 } from "./client";
 import {
   getValidToken,
+  googleHealthBackfillCursor,
+  googleHealthHardFailureCount,
   googleHealthTokenSource,
   handleCollectionFetchError,
+  recordGoogleHealthBackfillPage,
   runGoogleHealthCollection,
   upsertGoogleHealthMeasurements,
   type GoogleHealthMeasurementUpsert,
@@ -108,13 +114,6 @@ const METRIC_RESOURCES: MetricResource[] = [
     map: mapRespiratoryRate,
     verb: "fetchRespiratoryRate",
   },
-  {
-    dataType: GOOGLE_HEALTH_DATA_TYPES.heartRate,
-    map: mapHeartRate,
-    verb: "fetchHeartRate",
-    maxPages: GOOGLE_HEALTH_DENSE_MAX_PAGES,
-    intraday: true,
-  },
   {
     dataType: GOOGLE_HEALTH_DATA_TYPES.bloodGlucose,
     map: mapBloodGlucose,
@@ -133,8 +132,34 @@ const METRIC_RESOURCES: MetricResource[] = [
     map: mapWristTemperature,
     verb: "fetchSleepTemperature",
   },
+  // Last: the dense stream. A backfill finishes every light collection in
+  // its first slice and then works through this one slice by slice; ahead
+  // of them it held them back until the whole stream was in.
+  {
+    dataType: GOOGLE_HEALTH_DATA_TYPES.heartRate,
+    map: mapHeartRate,
+    verb: "fetchHeartRate",
+    maxPages: GOOGLE_HEALTH_DENSE_MAX_PAGES,
+    intraday: true,
+  },
 ];
 
+/**
+ * Whether a metric is walked resumably by a backfill: written page by page,
+ * and a spot reading whose sample time can mark how far the walk got.
+ */
+function isResumable(resource: MetricResource): boolean {
+  return resource.dataType.timeField === "sample";
+}
+
+/**
+ * The page ceilings of every resumable collection, summed: the most pages a
+ * backfill can ever spend on them across all of its attempts.
+ */
+export const GOOGLE_HEALTH_RESUMABLE_PAGE_CEILING = METRIC_RESOURCES.filter(
+  isResumable,
+).reduce((sum, r) => sum + (r.maxPages ?? GOOGLE_HEALTH_DEFAULT_MAX_PAGES), 0);
+
 export async function syncUserMetrics(
   userId: string,
   opts: GoogleHealthResourceSyncOptions = {},
@@ -245,6 +270,27 @@ async function syncMetricCollection(
   opts: GoogleHealthResourceSyncOptions,
 ): Promise<number> {
   let imported = 0;
+  // Inside a backfill a spot-reading collection keeps its place: it starts
+  // from the edge an earlier attempt reached and records its new edge after
+  // every page it writes (see `GoogleHealthBackfillCursor`). Its page ceiling
+  // then counts across attempts, so a cursor that never ends is still bounded.
+  const cursor = isResumable(resource)
+    ? googleHealthBackfillCursor(resource.verb)
+    : null;
+  const maxPages =
+    (resource.maxPages ?? GOOGLE_HEALTH_DEFAULT_MAX_PAGES) -
+    (cursor?.pagesSoFar ?? 0);
+  if (cursor && maxPages <= 0) {
+    getEvent()?.addWarning(
+      `google-health ${resource.verb}: backfill reached its page ceiling of ${resource.maxPages ?? GOOGLE_HEALTH_DEFAULT_MAX_PAGES} pages for ${userId}`,
+    );
+    noteGoogleHealthDeferred();
+    return 0;
+  }
+  // Once one page's write fails, the edge stays where it is for the rest of
+  // the walk: moving it past the failed page would leave that page's rows
+  // behind it for good.
+  let edgeHeld = false;
   try {
     await forEachDataPointPage(
       resource.dataType,
@@ -254,7 +300,8 @@ async function syncMetricCollection(
         start: resource.intraday
           ? (opts.intradayStart ?? opts.start)
           : opts.start,
-        maxPages: resource.maxPages,
+        maxPages,
+        ...(cursor ? { resumable: true, edge: cursor.edge } : {}),
       },
       async (points) => {
         const readings: GoogleHealthMeasurementUpsert[] = [];
@@ -269,11 +316,23 @@ async function syncMetricCollection(
             });
           }
         }
+        const failuresBefore = googleHealthHardFailureCount();
         imported += (
           await upsertGoogleHealthMeasurements(userId, readings, {
             deferRollup: opts.deferRollup,
           })
         ).imported;
+        if (!cursor || points.length === 0) return;
+        if (googleHealthHardFailureCount() !== failuresBefore) edgeHeld = true;
+        if (edgeHeld) return;
+        await recordGoogleHealthBackfillPage(resource.verb, {
+          first: googleHealthSampleInstant(points[0]!, resource.dataType, tz),
+          last: googleHealthSampleInstant(
+            points[points.length - 1]!,
+            resource.dataType,
+            tz,
+          ),
+        });
       },
     );
   } catch (err) {
diff --git a/src/lib/jobs/__tests__/google-health-backfill.test.ts b/src/lib/jobs/__tests__/google-health-backfill.test.ts
index 4e5e5a269..796893945 100644
--- a/src/lib/jobs/__tests__/google-health-backfill.test.ts
+++ b/src/lib/jobs/__tests__/google-health-backfill.test.ts
@@ -31,7 +31,13 @@ const {
   bossSend: vi.fn(),
   // Collections the mocked walk "finishes" in this attempt, added to the
   // resume set the way `runGoogleHealthCollection` adds them.
-  resumeState: { finishes: [] as string[], doneBefore: [] as string[] },
+  resumeState: {
+    finishes: [] as string[],
+    doneBefore: [] as string[],
+    /** Collections whose resume edge the mocked walk moves. */
+    advances: [] as string[],
+    collections: [] as Array<{ key: string; status: string }>,
+  },
 }));
 
 vi.mock("@/lib/db", () => ({ prisma: prismaMock }));
@@ -54,6 +60,7 @@ vi.mock("@/lib/safe-fetch", async (importOriginal) => {
 vi.mock("@/lib/google-health/sync-core", () => ({
   GOOGLE_HEALTH_INTEGRATION_KEY: "google-health",
   readGoogleHealthBackfillDone: () => new Set<string>(resumeState.doneBefore),
+  readGoogleHealthBackfillCursors: () => new Map(),
   runWithGoogleHealthBackfillResume: async (
     _userId: string,
     done: Set<string>,
@@ -61,7 +68,12 @@ vi.mock("@/lib/google-health/sync-core", () => ({
   ) => {
     const result = await fn();
     for (const key of resumeState.finishes) done.add(key);
-    return { result, skipped: [] };
+    return {
+      result,
+      skipped: [],
+      advanced: new Map(resumeState.advances.map((key) => [key, null])),
+      collections: resumeState.collections,
+    };
   },
 }));
 vi.mock("@/lib/google-health/sync", () => ({
@@ -71,8 +83,11 @@ vi.mock("@/lib/google-health/sync", () => ({
 
 import {
   GOOGLE_HEALTH_BACKFILL_MAX_SLICE,
+  GOOGLE_HEALTH_BACKFILL_THROTTLED_DELAY_SECONDS,
   runGoogleHealthBackfillForUser,
 } from "../google-health-backfill";
+import { GOOGLE_HEALTH_RESUMABLE_PAGE_CEILING } from "@/lib/google-health/sync-metrics";
+import { INTEGRATION_BACKFILL_CONTINUATION_DELAY_SECONDS } from "@/lib/jobs/integration-backfill-admission";
 import {
   GOOGLE_HEALTH_DATA_TYPES,
   forEachDataPointPage,
@@ -87,6 +102,8 @@ beforeEach(() => {
   bossSend.mockResolvedValue("job-next");
   resumeState.finishes = [];
   resumeState.doneBefore = [];
+  resumeState.advances = [];
+  resumeState.collections = [];
 });
 
 describe("runGoogleHealthBackfillForUser — verdict-gated marker", () => {
@@ -261,8 +278,71 @@ describe("runGoogleHealthBackfillForUser — slices", () => {
     expect(bossSend).not.toHaveBeenCalled();
   });
 
-  it("caps the chain at the number of collections plus two", () => {
-    expect(GOOGLE_HEALTH_BACKFILL_MAX_SLICE).toBe(17 + 2);
+  it("derives the chain's ceiling from the work a backfill can do", () => {
+    // Every collection once, plus every page the resumable collections may
+    // ever read (heart rate's 10 000 and four others' 1 000), plus slack.
+    expect(GOOGLE_HEALTH_BACKFILL_MAX_SLICE).toBe(
+      17 + GOOGLE_HEALTH_RESUMABLE_PAGE_CEILING + 2,
+    );
+    expect(GOOGLE_HEALTH_RESUMABLE_PAGE_CEILING).toBe(10_000 + 4 * 1000);
+  });
+
+  it("continues a slice that only moved a collection's edge", async () => {
+    resumeState.advances = ["fetchHeartRate"];
+    syncUserGoogleHealthMock.mockResolvedValue({ imported: 900, failed: true });
+
+    await expect(
+      runGoogleHealthBackfillForUser("u1", undefined, 7),
+    ).resolves.toEqual({ imported: 900, continued: true });
+    expect(bossSend).toHaveBeenCalledTimes(1);
+    expect(bossSend.mock.calls[0]![1]).toMatchObject({
+      data: { userId: "u1", slice: 8 },
+    });
+    expect(bossSend.mock.calls[0]![2]).toMatchObject({
+      startAfter: INTEGRATION_BACKFILL_CONTINUATION_DELAY_SECONDS,
+    });
+  });
+
+  it("waits longer before the next slice when this one ended on a rate limit", async () => {
+    resumeState.advances = ["fetchHeartRate"];
+    syncUserGoogleHealthMock.mockResolvedValue({ imported: 10, failed: true });
+    // The slice ended the way a resumable walk ends it when Google keeps
+    // answering 429 past every wait.
+    const client = await import("@/lib/google-health/client");
+    const spy = vi
+      .spyOn(client, "googleHealthSliceBudget")
+      .mockImplementation(() => ({
+        ms: 300_000,
+        deadline: null,
+        maxPages: 500,
+        pages: 3,
+        stopReason: "rate_limited",
+        now: Date.now,
+      }));
+    try {
+      await runGoogleHealthBackfillForUser("u1");
+    } finally {
+      spy.mockRestore();
+    }
+    expect(bossSend.mock.calls[0]![2]).toMatchObject({
+      startAfter: GOOGLE_HEALTH_BACKFILL_THROTTLED_DELAY_SECONDS,
+    });
+  });
+
+  it("names where it is stuck when a slice moved nothing", async () => {
+    resumeState.collections = [
+      { key: "fetchWeight", status: "done" },
+      { key: "fetchHeartRate", status: "failed" },
+      { key: "fetchBloodGlucose", status: "deferred" },
+    ];
+    syncUserGoogleHealthMock.mockResolvedValue({ imported: 0, failed: true });
+
+    await expect(
+      runGoogleHealthBackfillForUser("u1", undefined, 3),
+    ).rejects.toThrow(
+      /marker not stamped \(no progress in slice 3; fetchHeartRate:failed,fetchBloodGlucose:deferred\)/,
+    );
+    expect(bossSend).not.toHaveBeenCalled();
   });
 
   it("stamps the marker on the slice that finishes the history", async () => {
diff --git a/src/lib/jobs/google-health-backfill.ts b/src/lib/jobs/google-health-backfill.ts
index 4f3a00294..05a3a27bd 100644
--- a/src/lib/jobs/google-health-backfill.ts
+++ b/src/lib/jobs/google-health-backfill.ts
@@ -21,6 +21,7 @@ import {
   integrationBackfillSourceOptions,
 } from "@/lib/jobs/integration-backfill-admission";
 import {
+  readGoogleHealthBackfillCursors,
   readGoogleHealthBackfillDone,
   runWithGoogleHealthBackfillResume,
 } from "@/lib/google-health/sync-core";
@@ -29,7 +30,12 @@ import {
   syncUserGoogleHealth,
 } from "@/lib/google-health/sync";
 import { GOOGLE_HEALTH_SYNC_LOCK_WAIT_MS } from "@/lib/google-health/sync-lock";
-import { runWithGoogleHealthStop } from "@/lib/google-health/client";
+import {
+  googleHealthSliceBudget,
+  runWithGoogleHealthStop,
+} from "@/lib/google-health/client";
+import { GOOGLE_HEALTH_RESUMABLE_PAGE_CEILING } from "@/lib/google-health/sync-metrics";
+import { reportJobProgress } from "@/lib/jobs/job-observer";
 import { GOOGLE_HEALTH_COLLECTION_KEYS } from "@/lib/google-health/collection-keys";
 
 export const GOOGLE_HEALTH_BACKFILL_QUEUE = "google-health-backfill";
@@ -42,15 +48,52 @@ export const GOOGLE_HEALTH_BACKFILL_QUEUE = "google-health-backfill";
 export const GOOGLE_HEALTH_BACKFILL_CONCURRENCY = 1;
 
 /**
- * The highest slice a backfill chain may reach. Every continued slice has
- * finished at least one more collection than the one before it, so a healthy
- * chain is at most one slice per collection long; the two extra slices are
- * slack for the first one and the one that stamps the marker. A slice past
- * this is a chain that counts progress it does not make, and it fails rather
- * than queueing another.
+ * One slice of a backfill: how long it walks and how many pages it reads
+ * before it lets go of the account and hands the rest to the next slice.
+ *
+ * Far inside the admission job's expiry (sixteen hours) on purpose. A slice
+ * holds the account's sync lock while it walks, and the hourly sync of that
+ * account waits for the lock (`GOOGLE_HEALTH_POLL_LOCK_WAIT_MS`), so a slice
+ * has to be short enough for the hourly sync to get its turn: before slices,
+ * one attempt held the lock for as long as the import ran and every hourly
+ * sync of the account in that time was skipped. The page budget keeps a
+ * slice on a fast link from spending a whole quota window in one go.
+ */
+export const GOOGLE_HEALTH_BACKFILL_SLICE_MS = 5 * 60 * 1000;
+export const GOOGLE_HEALTH_BACKFILL_SLICE_PAGES = 500;
+
+/**
+ * The pause before the next slice when this one ended on a rate limit it
+ * could not wait out: long enough for Google's per-minute window to refill
+ * several times over, so the next slice does not open on the same 429.
+ */
+export const GOOGLE_HEALTH_BACKFILL_THROTTLED_DELAY_SECONDS = 5 * 60;
+
+/**
+ * The highest slice a backfill chain may reach, derived from the work a
+ * backfill can do rather than guessed.
+ *
+ * A slice is continued only when it made progress that is on disk: it
+ * finished a collection, or it moved a resumable collection's edge after
+ * writing at least one page. Collections finish once each, and a resumable
+ * collection's pages are capped across all attempts by its page ceiling
+ * (`GOOGLE_HEALTH_RESUMABLE_PAGE_CEILING`, the sum of them). So no chain of
+ * progressing slices is longer than the collections plus those pages; the two
+ * extra are slack for the first slice and the one that stamps the marker. In
+ * practice a chain is a handful of slices per year of dense history. A slice
+ * past this is counting progress it does not make, and fails rather than
+ * queueing another.
  */
 export const GOOGLE_HEALTH_BACKFILL_MAX_SLICE =
-  GOOGLE_HEALTH_COLLECTION_KEYS.length + 2;
+  GOOGLE_HEALTH_COLLECTION_KEYS.length +
+  GOOGLE_HEALTH_RESUMABLE_PAGE_CEILING +
+  2;
+
+/** Test seam: a slice's budget, when not the production one. */
+export interface GoogleHealthBackfillSliceOptions {
+  sliceMs?: number;
+  slicePages?: number;
+}
 
 export interface GoogleHealthBackfillPayload {
   userId: string;
@@ -58,42 +101,40 @@ export interface GoogleHealthBackfillPayload {
 }
 
 /**
- * Per-user backfill handler. Runs a full-history sync for one account and
- * stamps `backfillCompletedAt` ONLY on a clean run, so the discovery query
- * drops it. Idempotent: the per-resource upserts are key-stable, so a re-run
- * (e.g. a reboot mid-walk) overwrites rather than duplicating. Mirrors
- * `runFitbitBackfillForUser`.
+ * Per-user backfill handler. Runs one slice of a full-history sync for one
+ * account and stamps `backfillCompletedAt` ONLY on a clean run, so the
+ * discovery query drops it. Idempotent: the per-resource upserts are
+ * key-stable, so a re-run (e.g. a reboot mid-walk) overwrites rather than
+ * duplicating. Mirrors `runFitbitBackfillForUser`.
  *
  * Verdict-gated: a partial hard failure (one collection 400ing, a write
- * failing) THROWS so pg-boss retries the job — stamping the marker over a
- * partial walk would freeze the gap in forever. A connection parked at
- * `error_reauth` is NOT clean either, but throwing against a dead grant would
- * just burn the retry budget on the same no-op: return WITHOUT stamping — the
- * boot discovery re-enqueues the account on the next boot, and the stamp lands
- * once the user reconnects and a clean walk completes.
+ * failing) is not complete, and stamping the marker over a partial walk would
+ * freeze the gap in forever. A connection parked at `error_reauth` is NOT
+ * clean either, but throwing against a dead grant would just burn the retry
+ * budget on the same no-op: return WITHOUT stamping — the boot discovery
+ * re-enqueues the account on the next boot, and the stamp lands once the user
+ * reconnects and a clean walk completes.
  *
- * `shouldStop` is the admission job's budget (`jobBudget`). A per-minute
- * heart-rate history runs to thousands of pages, and the walk asks it before
- * every page: once it says stop, the walk ends where it is, the cycle reports
- * itself truncated, and this throws like any other incomplete run, without
- * the stamp. The rows already written stay.
+ * Resumable at two grains (`GoogleHealthBackfillCursor`): every collection the
+ * walk finishes cleanly is noted in `backfillProgress.done` and skipped from
+ * then on, and every spot-reading collection notes the edge it has written up
+ * to after each page, so the next attempt starts there instead of at the
+ * newest page. The note is cleared once the stamp lands, and on every
+ * reconnect.
  *
- * Resumable: every collection the walk finishes cleanly is noted in
- * `backfillProgress`, and the next attempt (the pg-boss retry, or the next
- * boot's discovery) skips those and walks only what is left
- * (`runWithGoogleHealthBackfillResume`). The note is cleared once the stamp
- * lands, and on every reconnect.
+ * Runs in slices. A slice walks until its own budget is spent
+ * (`GOOGLE_HEALTH_BACKFILL_SLICE_MS` / `_PAGES`), Google throttles it past
+ * what a wait covers, or the job's budget (`shouldStop`) runs out, and then
+ * lets go of the account. A slice that made progress on disk (a collection
+ * finished, an edge moved) is not a failure: it sends the next slice
+ * (`slice + 1`) and returns `continued`, without the error line or the
+ * queue's failure count. Only a slice that moved nothing throws, with what
+ * each collection came to in the message, because that one is stuck: the
+ * pg-boss retry and, after it, the next boot take it from there. The chain is
+ * capped at `GOOGLE_HEALTH_BACKFILL_MAX_SLICE`.
  *
- * Runs in slices: an attempt that ends before the whole history is in but
- * finished at least one more collection than it started with made progress.
- * It is not a failure: it sends the next slice (`slice + 1`) and returns
- * `continued`, without the error line or the queue's failure count. Only an
- * attempt that finished nothing new throws, because that one is stuck: the
- * pg-boss retry and, after it, the next boot take it from there. Progress is
- * counted only once it is persisted (`runGoogleHealthCollection` adds a
- * collection to `done` after its note is written), and the chain is capped at
- * `GOOGLE_HEALTH_BACKFILL_MAX_SLICE`: a slice past it throws instead of
- * running or sending another.
+ * What the slice did is annotated on the run's event as
+ * `googleHealth.backfill.slice` (see `docs/integrations/google-health.md`).
  *
  * Never beside another run of the same account: the sync takes the account's
  * lock, waiting a bounded time for an hourly or manual run to finish. If the
@@ -104,6 +145,7 @@ export async function runGoogleHealthBackfillForUser(
   userId: string,
   shouldStop: () => boolean = () => false,
   slice: number = 0,
+  sliceOptions: GoogleHealthBackfillSliceOptions = {},
 ): Promise<{ imported: number; continued?: boolean }> {
   if (slice > GOOGLE_HEALTH_BACKFILL_MAX_SLICE) {
     annotate({
@@ -142,22 +184,56 @@ export async function runGoogleHealthBackfillForUser(
     return { imported: 0 };
   }
   const done = readGoogleHealthBackfillDone(connection?.backfillProgress);
+  const cursors = readGoogleHealthBackfillCursors(connection?.backfillProgress);
   const doneBefore = done.size;
 
+  const budget = googleHealthSliceBudget(
+    sliceOptions.sliceMs ?? GOOGLE_HEALTH_BACKFILL_SLICE_MS,
+    sliceOptions.slicePages ?? GOOGLE_HEALTH_BACKFILL_SLICE_PAGES,
+  );
+  const startedAt = Date.now();
   const {
     result: { imported, failed, busy },
     skipped,
-  } = await runWithGoogleHealthBackfillResume(userId, done, () =>
-    runWithGoogleHealthStop(shouldStop, () =>
-      syncUserGoogleHealth(userId, {
-        fullSync: true,
-        waitForLockMs: GOOGLE_HEALTH_SYNC_LOCK_WAIT_MS,
-      }),
-    ),
+    advanced,
+    collections,
+  } = await runWithGoogleHealthBackfillResume(
+    userId,
+    done,
+    () =>
+      runWithGoogleHealthStop(
+        shouldStop,
+        () =>
+          syncUserGoogleHealth(userId, {
+            fullSync: true,
+            waitForLockMs: GOOGLE_HEALTH_SYNC_LOCK_WAIT_MS,
+          }),
+        budget,
+      ),
+    cursors,
   );
-  if (skipped.length > 0) {
-    annotate({ meta: { "googleHealth.backfill.resumedPast": skipped } });
-  }
+
+  const finished = done.size - doneBefore;
+  const sliceReport = {
+    slice,
+    elapsedMs: Date.now() - startedAt,
+    pages: budget.pages,
+    stopReason: budget.stopReason,
+    imported,
+    collectionsDone: done.size,
+    collectionsTotal: GOOGLE_HEALTH_COLLECTION_KEYS.length,
+    collectionsFinished: finished,
+    resumedPast: skipped.length,
+    collections,
+    // Where each unfinished resumable collection has got to, after this slice.
+    edges: Object.fromEntries([...cursors].map(([key, c]) => [key, c.at])),
+  };
+  annotate({ meta: { "googleHealth.backfill.slice": sliceReport } });
+  reportJobProgress({
+    google_health_backfill_slice: slice,
+    google_health_backfill_pages: budget.pages,
+    google_health_backfill_collections_done: done.size,
+  });
 
   if (busy) {
     throw new Error(
@@ -166,10 +242,10 @@ export async function runGoogleHealthBackfillForUser(
   }
 
   if (failed) {
-    // `done` is the resume set this attempt added to as it finished
-    // collections; a larger set than it started with is progress.
-    const finished = done.size - doneBefore;
-    if (finished > 0 && slice + 1 <= GOOGLE_HEALTH_BACKFILL_MAX_SLICE) {
+    // Progress is what this slice put on disk: collections finished, and
+    // edges moved. Either is enough to go on; neither means stuck.
+    const progressed = finished > 0 || advanced.size > 0;
+    if (progressed && slice + 1 <= GOOGLE_HEALTH_BACKFILL_MAX_SLICE) {
       const boss = getGlobalBoss();
       const sent = boss
         ? await enqueueIntegrationBackfillAdmission(
@@ -182,7 +258,9 @@ export async function runGoogleHealthBackfillForUser(
                 slice: slice + 1,
               },
             },
-            INTEGRATION_BACKFILL_CONTINUATION_DELAY_SECONDS,
+            budget.stopReason === "rate_limited"
+              ? GOOGLE_HEALTH_BACKFILL_THROTTLED_DELAY_SECONDS
+              : INTEGRATION_BACKFILL_CONTINUATION_DELAY_SECONDS,
           )
         : null;
       if (sent) {
@@ -192,8 +270,10 @@ export async function runGoogleHealthBackfillForUser(
             details: {
               imported,
               slice,
+              stopReason: budget.stopReason,
               collectionsFinished: finished,
               collectionsDone: done.size,
+              edgesMoved: [...advanced.keys()],
             },
           },
         });
@@ -202,12 +282,23 @@ export async function runGoogleHealthBackfillForUser(
       // No follow-up could be queued; fall through to the retry path so the
       // work is not dropped.
     }
-    // No collection finished in this attempt: the backfill is stuck, not
-    // slow. Surface through the pg-boss retry path (retryLimit 3, backoff).
-    // If the failure parked the connection at error_reauth meanwhile, the
-    // next attempt takes the reauth return above instead of failing again.
+    // Nothing moved in this slice: the backfill is stuck, not slow. Surface
+    // through the pg-boss retry path (retryLimit 3, backoff) with what each
+    // collection came to, so the log line says where it is stuck. If the
+    // failure parked the connection at error_reauth meanwhile, the next
+    // attempt takes the reauth return above instead of failing again.
+    annotate({
+      action: {
+        name: "google_health.backfill.stuck",
+        details: { slice, stopReason: budget.stopReason },
+      },
+    });
+    const where = collections
+      .filter((c) => c.status !== "done")
+      .map((c) => `${c.key}:${c.status}`)
+      .join(",");
     throw new Error(
-      `google-health backfill incomplete for user ${userId} — marker not stamped`,
+      `google-health backfill incomplete for user ${userId} — marker not stamped (no progress in slice ${slice}${budget.stopReason ? `, stopped on ${budget.stopReason}` : ""}${where ? `; ${where}` : ""})`,
     );
   }
 
@@ -219,7 +310,7 @@ export async function runGoogleHealthBackfillForUser(
   annotate({
     action: {
       name: "google_health.backfill.complete",
-      details: { imported },
+      details: { imported, slice },
     },
   });
   return { imported };
diff --git a/src/lib/jobs/reminder/google-health-sync.ts b/src/lib/jobs/reminder/google-health-sync.ts
index f58329bc0..7ac2e7d0f 100644
--- a/src/lib/jobs/reminder/google-health-sync.ts
+++ b/src/lib/jobs/reminder/google-health-sync.ts
@@ -15,6 +15,7 @@ import {
   isGoogleHealthParked,
   syncUserGoogleHealth,
 } from "@/lib/google-health/sync";
+import { GOOGLE_HEALTH_POLL_LOCK_WAIT_MS } from "@/lib/google-health/sync-lock";
 import { enqueueReminderSatisfy } from "@/lib/jobs/reminder-satisfy";
 import { cleanupExpiredGoogleHealthOAuthStates } from "@/lib/jobs/google-health-oauth-state-cleanup";
 import {
@@ -69,9 +70,15 @@ export async function handleGoogleHealthSync(
             }
 
             try {
-              const result = await syncUserGoogleHealth(userId);
+              // A backfill holds the account for one slice at a time, so
+              // the tick waits for the slice to end rather than skipping the
+              // account for as long as the whole import runs.
+              const result = await syncUserGoogleHealth(userId, {
+                waitForLockMs: GOOGLE_HEALTH_POLL_LOCK_WAIT_MS,
+              });
               // Another run of this account (its backfill, a manual sync)
-              // holds the account; this tick leaves it to that run.
+              // still held the account after the wait; this tick leaves it
+              // to that run.
               if (result.busy) return { status: "skipped", imported: 0 };
               const parked =
                 result.failed &&
diff --git a/tests/integration/google-health-backfill-rate-limit.test.ts b/tests/integration/google-health-backfill-rate-limit.test.ts
index 2cf7bd9a1..3ddb049fa 100644
--- a/tests/integration/google-health-backfill-rate-limit.test.ts
+++ b/tests/integration/google-health-backfill-rate-limit.test.ts
@@ -57,6 +57,8 @@ const fake = vi.hoisted(() => ({
   throttledPages: new Set<number>(),
   /** Revoke the current access token when this heart-rate page is asked. */
   revokeAtPage: -1,
+  /** Answer every heart-rate request with a 500. */
+  failHeartRate: false,
   /** Hold the request for this heart-rate page until `release` is called. */
   holdAtPage: -1,
   release: null as null | (() => void),
@@ -138,13 +140,24 @@ vi.mock("@/lib/safe-fetch", async (importOriginal) => {
             { "retry-after": "0" },
           );
         }
+        if (fake.failHeartRate) {
+          return json({ error: { code: 500, status: "INTERNAL" } }, 500);
+        }
         if (page === fake.holdAtPage) {
           fake.holdAtPage = -1;
           await fake.held;
         }
-        const end = Math.min(fake.heartRatePoints, (page + 1) * 10);
+        // Newest first, one point a minute; a resumed walk's `<=` edge
+        // filter starts the list at the edge.
+        const edge = /physical_time <= "([^"]+)"/.exec(
+          u.searchParams.get("filter") ?? "",
+        )?.[1];
+        const first = edge
+          ? Math.ceil((fake.now - Date.parse(edge)) / 60_000)
+          : 0;
+        const end = Math.min(fake.heartRatePoints, first + (page + 1) * 10);
         const dataPoints = [];
-        for (let g = page * 10; g < end; g++) {
+        for (let g = first + page * 10; g < end; g++) {
           dataPoints.push({
             name: `users/me/dataTypes/heart-rate/dataPoints/${1_000_000 + g}`,
             heartRate: {
@@ -221,6 +234,7 @@ beforeEach(async () => {
   fake.throttledPages = new Set();
   fake.revokeAtPage = -1;
   fake.holdAtPage = -1;
+  fake.failHeartRate = false;
   fake.release = null;
   fake.held = null;
   fake.requestsByPath = new Map();
@@ -398,8 +412,19 @@ describe("Google Health backfill under rate limits and token expiry (#1194)", ()
     );
     expect(done).not.toContain("fetchHeartRate");
 
+    // And the heart-rate stream keeps the edge it reached: the oldest of
+    // the thirty samples it wrote.
+    expect(
+      (afterFirst?.backfillProgress as { cursors: Record<string, unknown> })
+        .cursors.fetchHeartRate,
+    ).toMatchObject({
+      at: new Date(fake.now - 29 * 60_000).toISOString(),
+      pages: 3,
+    });
+
     // Second attempt, the queued slice: the finished collections are not
-    // read again.
+    // read again, and the stream starts at its edge, not at its newest page:
+    // the 31 samples from the edge on are four pages, not six.
     fake.requestsByPath = new Map();
     await runGoogleHealthBackfillForUser(USER, undefined, 1);
 
@@ -408,7 +433,7 @@ describe("Google Health backfill under rate limits and token expiry (#1194)", ()
     expect(
       fake.requestsByPath.get("steps/dataPoints:dailyRollUp"),
     ).toBeUndefined();
-    expect(fake.requestsByPath.get("heart-rate/dataPoints")).toBe(6);
+    expect(fake.requestsByPath.get("heart-rate/dataPoints")).toBe(4);
     expect(await pulseRows()).toBe(60);
     const afterSecond =
       await getPrismaClient().googleHealthConnection.findUnique({
@@ -418,7 +443,7 @@ describe("Google Health backfill under rate limits and token expiry (#1194)", ()
     expect(afterSecond?.backfillProgress).toBeNull();
   });
 
-  it("keeps failing a backfill whose slice finished nothing new", async () => {
+  it("continues a slice that only moved the stream's edge, and fails one that moved nothing", async () => {
     const { runGoogleHealthBackfillForUser } =
       await import("@/lib/jobs/google-health-backfill");
 
@@ -428,13 +453,29 @@ describe("Google Health backfill under rate limits and token expiry (#1194)", ()
     await runGoogleHealthBackfillForUser(USER, stopAtThirdPage);
     expect(sent.jobs).toHaveLength(1);
 
-    // The next slice cannot get through the heart-rate stream either: no
-    // collection finishes, so this one is stuck and says so.
+    // The next slice finishes no collection either, but it moves the edge
+    // thirty samples further back: progress, so it continues.
     fake.requestsByPath = new Map();
     await expect(
       runGoogleHealthBackfillForUser(USER, stopAtThirdPage, 1),
-    ).rejects.toThrow(/incomplete/);
-    expect(sent.jobs).toHaveLength(1);
+    ).resolves.toMatchObject({ continued: true });
+    expect(sent.jobs).toHaveLength(2);
+
+    // A slice whose every heart-rate request fails moves nothing: it is
+    // stuck, says where, and queues nothing.
+    const { GOOGLE_HEALTH_TRANSIENT_RETRY } =
+      await import("@/lib/google-health/client");
+    const baseDelay = GOOGLE_HEALTH_TRANSIENT_RETRY.baseDelayMs;
+    GOOGLE_HEALTH_TRANSIENT_RETRY.baseDelayMs = 0;
+    fake.failHeartRate = true;
+    try {
+      await expect(
+        runGoogleHealthBackfillForUser(USER, undefined, 2),
+      ).rejects.toThrow(/no progress in slice 2; fetchHeartRate:failed/);
+    } finally {
+      GOOGLE_HEALTH_TRANSIENT_RETRY.baseDelayMs = baseDelay;
+    }
+    expect(sent.jobs).toHaveLength(2);
     const row = await getPrismaClient().googleHealthConnection.findUnique({
       where: { userId: USER },
     });
@@ -459,27 +500,32 @@ describe("Google Health backfill under rate limits and token expiry (#1194)", ()
     }
     expect(fake.holdAtPage).toBe(-1);
 
-    const requestsBefore = [...fake.requestsByPath.values()].reduce(
-      (a, b) => a + b,
-      0,
-    );
+    const total = () =>
+      [...fake.requestsByPath.values()].reduce((a, b) => a + b, 0);
+    const requestsBefore = total();
     const manual = await syncUserGoogleHealth(USER);
     expect(manual.busy).toBe(true);
 
-    const hourly = await handleGoogleHealthSync([] as never);
-    expect(hourly).toMatchObject({
-      ok: true,
-      did: { users_skipped: 1, users_parked: 0, users_failed: 0 },
+    // The hourly poll waits for the account instead of skipping it: it does
+    // nothing while the backfill holds the lock ...
+    let hourlySettled = false;
+    const hourly = handleGoogleHealthSync([] as never).finally(() => {
+      hourlySettled = true;
     });
-    const requestsAfter = [...fake.requestsByPath.values()].reduce(
-      (a, b) => a + b,
-      0,
-    );
-    expect(requestsAfter).toBe(requestsBefore);
+    await new Promise((r) => setTimeout(r, 2_500));
+    expect(hourlySettled).toBe(false);
+    expect(total()).toBe(requestsBefore);
 
+    // ... and runs once the backfill lets go.
     fake.release?.();
     await backfill;
+    const requestsAfterBackfill = total();
+    expect(await hourly).toMatchObject({
+      ok: true,
+      did: { users_skipped: 0, users_parked: 0, users_failed: 0 },
+    });
+    expect(total()).toBeGreaterThan(requestsAfterBackfill);
     expect(await pulseRows()).toBe(60);
     expect(await ledgerState()).toBe("connected");
-  });
+  }, 60_000);
 });