diff --git a/src/lib/environment/__tests__/air-quality-history.test.ts b/src/lib/environment/__tests__/air-quality-history.test.ts
index 4b58cccb4..2d96853e5 100644
--- a/src/lib/environment/__tests__/air-quality-history.test.ts
+++ b/src/lib/environment/__tests__/air-quality-history.test.ts
@@ -1,19 +1,19 @@
 /**
  * v1.42 — the air-quality history backfill's pure parts: how pending days
  * are cut into request ranges, what a range weighs, the ceilings that keep
- * the history from taking the nightly fetch's room, where a day without a
- * row is placed, and when an account is offered a run again.
+ * the history from taking the nightly fetch's room, the entry-day snapshot a
+ * chain hands on, and when an account is offered a run again.
  */
 import { describe, expect, it } from "vitest";
 
 import {
   AIR_QUALITY_HISTORY_ACCOUNT_DAY_CALLS,
-  historyRangeWeight,
-  historyRequestFits,
+  AIR_QUALITY_HISTORY_CEILING,
   planHistoryRanges,
   readAirQualityHistoryState,
-  resolveHistoryLocation,
+  readEntryDaysSnapshot,
 } from "../air-quality-history";
+import { airQualityChunkWeight } from "../open-meteo-air-quality";
 import { historyDue } from "@/lib/jobs/environment-air-quality-history";
 import { shiftDateKey } from "@/lib/tz/format";
 
@@ -64,100 +64,35 @@ describe("planHistoryRanges", () => {
     const days = daysFrom("2023-01-01", 122, 3);
     const ranges = planHistoryRanges(days);
     const ranged = ranges.reduce(
-      (sum, r) => sum + historyRangeWeight(r, []),
+      (sum, r) => sum + airQualityChunkWeight(r.startDate, r.endDate),
       0,
     );
-    const perDay =
-      days.length *
-      historyRangeWeight(
-        { startDate: days[0], endDate: days[0], days: [days[0]] },
-        [],
-      );
+    const perDay = days.length * airQualityChunkWeight(days[0], days[0]);
     expect(ranged).toBeLessThan(perDay / 4);
   });
 });
 
-describe("historyRangeWeight", () => {
-  it("adds the weather only over the span of the days without a row", () => {
-    const range = {
-      startDate: "2023-01-01",
-      endDate: "2023-03-31",
-      days: ["2023-01-01", "2023-03-31"],
-    };
-    const airOnly = historyRangeWeight(range, []);
-    expect(airOnly).toBeCloseTo((1.7 * 90) / 14);
-    // One missing day: one weather request at its minimum weight (12 vars).
-    expect(historyRangeWeight(range, ["2023-03-31"])).toBeCloseTo(
-      airOnly + 1.2,
-    );
-  });
-});
-
-describe("historyRequestFits", () => {
-  it("admits a request under every ceiling", () => {
-    expect(historyRequestFits({}, 10)).toBe(true);
-  });
-
-  it("holds the account to three quarters of its daily share", () => {
+describe("the history's ceiling", () => {
+  it("holds the history to three quarters of the account's share and half of each instance window", () => {
     expect(AIR_QUALITY_HISTORY_ACCOUNT_DAY_CALLS).toBe(300);
-    expect(historyRequestFits({ "account-day": 295 }, 5)).toBe(true);
-    expect(historyRequestFits({ "account-day": 295 }, 5.1)).toBe(false);
-  });
-
-  it("holds the history to half of each instance window", () => {
-    expect(historyRequestFits({ minute: 245 }, 5)).toBe(true);
-    expect(historyRequestFits({ minute: 246 }, 5)).toBe(false);
-    expect(historyRequestFits({ hour: 1999 }, 2)).toBe(false);
-    expect(historyRequestFits({ day: 3995 }, 10)).toBe(false);
+    expect(AIR_QUALITY_HISTORY_CEILING).toEqual({
+      instanceShare: 0.5,
+      accountDayCalls: 300,
+    });
   });
 });
 
-describe("resolveHistoryLocation", () => {
-  const home = {
-    lat: 51.5,
-    lon: 7.2,
-    label: "Home",
-    timezone: "Europe/Berlin",
-    since: "2026-09-01",
-  };
-  const trip = {
-    startDate: "2024-07-01",
-    endDate: "2024-07-14",
-    lat: 38.7,
-    lon: -9.1,
-    label: "Lisbon",
-  };
-
-  it("places a day of a trip at the trip", () => {
-    expect(resolveHistoryLocation("2024-07-05", home, [trip])).toMatchObject({
-      lat: 38.7,
-      source: "TRAVEL",
-    });
-  });
-
-  it("places a day from the home's effective date on at the home", () => {
-    expect(resolveHistoryLocation("2026-09-01", home, [trip])).toMatchObject({
-      lat: 51.5,
-      source: "HOME",
-    });
-  });
-
-  it("leaves a day before the home was set without a place, unless a period covers it", () => {
-    expect(resolveHistoryLocation("2026-08-31", home, [trip])).toBeNull();
-    expect(resolveHistoryLocation("2020-03-01", home, [trip])).toBeNull();
-    expect(resolveHistoryLocation("2024-07-14", home, [trip])).toMatchObject({
-      source: "TRAVEL",
-    });
-  });
-
-  it("places every day at a home stored without an effective date", () => {
-    expect(
-      resolveHistoryLocation("2015-01-01", { ...home, since: null }, []),
-    ).toMatchObject({ lat: 51.5, source: "HOME" });
-  });
-
-  it("places nothing without a home or a period", () => {
-    expect(resolveHistoryLocation("2020-03-01", null, [trip])).toBeNull();
+describe("entry-day snapshot", () => {
+  it("reads a snapshot from a payload and refuses anything else", () => {
+    const snapshot = {
+      timezone: "Europe/Berlin",
+      cutoff: "2026-10-01",
+      days: ["2024-01-01"],
+    };
+    expect(readEntryDaysSnapshot(snapshot)).toEqual(snapshot);
+    expect(readEntryDaysSnapshot(undefined)).toBeNull();
+    expect(readEntryDaysSnapshot({ ...snapshot, days: [1] })).toBeNull();
+    expect(readEntryDaysSnapshot({ ...snapshot, cutoff: 1 })).toBeNull();
   });
 });
 
diff --git a/src/lib/environment/__tests__/request-budget.test.ts b/src/lib/environment/__tests__/request-budget.test.ts
index b0426a31e..49fc49fc8 100644
--- a/src/lib/environment/__tests__/request-budget.test.ts
+++ b/src/lib/environment/__tests__/request-budget.test.ts
@@ -45,6 +45,7 @@ import {
   admitWeight,
   openMeteoCallWeight,
   reserveOpenMeteoCalls,
+  windowsUnderCeiling,
   type BudgetBucket,
 } from "../request-budget";
 
@@ -134,3 +135,44 @@ describe("the per-account share", () => {
     expect(await reserveOpenMeteoCalls(1)).toBe(true);
   });
 });
+
+describe("a caller's own ceiling", () => {
+  const ceiling = { instanceShare: 0.5, accountDayCalls: 300 };
+
+  it("lowers each instance window to its share and the account's day to its calls", () => {
+    const windows = windowsUnderCeiling(
+      [...OPEN_METEO_BUDGET_WINDOWS, OPEN_METEO_ACCOUNT_DAY_WINDOW],
+      ceiling,
+    );
+    expect(windows.map((w) => [w.name, w.limit, w.windowMs])).toEqual([
+      ["minute", 250, 60_000],
+      ["hour", 2_000, 3_600_000],
+      ["day", 4_000, 86_400_000],
+      ["account-day", 300, 86_400_000],
+    ]);
+    expect(windowsUnderCeiling(OPEN_METEO_BUDGET_WINDOWS, undefined)).toBe(
+      OPEN_METEO_BUDGET_WINDOWS,
+    );
+  });
+
+  it("refuses past the ceiling what the budget alone would admit, and charges nothing", async () => {
+    store.clear();
+    const later = new Date(Date.now() + 3_600_000);
+    store.set("open-meteo-budget:account:acct-c:day", {
+      count: 295 * 100,
+      resetAt: later,
+    });
+    expect(await reserveOpenMeteoCalls(5, "acct-c", ceiling)).toBe(true);
+    expect(await reserveOpenMeteoCalls(0.1, "acct-c", ceiling)).toBe(false);
+    expect(store.get("open-meteo-budget:account:acct-c:day")!.count).toBe(
+      300 * 100,
+    );
+    // The same request without the ceiling is still inside the budget.
+    expect(await reserveOpenMeteoCalls(0.1, "acct-c")).toBe(true);
+
+    store.clear();
+    store.set("open-meteo-budget:minute", { count: 246 * 100, resetAt: later });
+    expect(await reserveOpenMeteoCalls(5, "acct-c", ceiling)).toBe(false);
+    expect(await reserveOpenMeteoCalls(4, "acct-c", ceiling)).toBe(true);
+  });
+});
diff --git a/src/lib/environment/air-quality-history.ts b/src/lib/environment/air-quality-history.ts
index 7d2ea80a2..c192eff28 100644
--- a/src/lib/environment/air-quality-history.ts
+++ b/src/lib/environment/air-quality-history.ts
@@ -15,13 +15,15 @@
  *     (only the air-quality part is fetched then, as the nightly gap fill
  *     does);
  *   - otherwise in the dated location period that covers it, else at the
- *     home, but the home only from `homeSince` on (or on every day when no
- *     `homeSince` is stored). A day before the home was set is never placed
- *     there: the weather and air of a place the person was not at would be
- *     wrong data in the correlations, the Coach and the day view, and an
- *     empty day is honest where a wrong one is not. Such a day is filled
- *     only when a period covers it. A day without a row gets its weather row
- *     with the air quality, because the air quality is stored on it.
+ *     home, but the home only from `homeSince` on, by the same rule the
+ *     nightly fetch places a day with (`resolveLocationForDay`). A home
+ *     without a `homeSince` places no day at all, there as here. A day
+ *     before the home was set is never placed there: the weather and air of
+ *     a place the person was not at would be wrong data in the
+ *     correlations, the Coach and the day view, and an empty day is honest
+ *     where a wrong one is not. Such a day is filled only when a period
+ *     covers it. A day without a row gets its weather row with the air
+ *     quality, because the air quality is stored on it.
  *
  * A day inside a period whose sealed location does not open is skipped (fail
  * closed, as in the service), and so is a day with no place at all; neither
@@ -40,7 +42,19 @@
  * over 14 (`openMeteoCallWeight`), so a lone day costs as much as two weeks:
  * joining short gaps is free, splitting long ones saves the gap. The newest
  * ranges go first, so the window the correlations read fills first. The
- * weather of a range is asked only over the span of its days without a row.
+ * weather of a range is asked only over the span of its days without a row,
+ * and before its air quality: a weather request the feed or the budget
+ * refuses then costs no air-quality call, and when the air quality fails
+ * after the weather came back, the weather rows are stored without it, so
+ * the next run asks for the air quality alone and nothing paid is asked for
+ * twice. A day the archive answer leaves out gets no row: it stays pending
+ * rather than carrying an empty weather row that nothing would fill again.
+ *
+ * The first request the feed refuses (a 429, a 5xx, a network error) ends
+ * the run with status `error` and no follow-up; the next nightly discovery
+ * tries again. Before every range the run re-reads the module, the
+ * account's air-quality switch and `ENVIRONMENT_AIR_QUALITY_DISABLED`, so
+ * switching any of them off stops a run between two ranges.
  *
  * ## Budget
  *
@@ -48,7 +62,11 @@
  * share (`request-budget.ts`). On top of that the history holds itself to
  * {@link AIR_QUALITY_HISTORY_ACCOUNT_DAY_CALLS} of the account's 400 daily
  * calls and to half of each instance window, so the nightly fetch, the gap
- * fill and a backfill someone asked for keep their room. A run that reaches a
+ * fill and a backfill someone asked for keep their room. The ceiling is
+ * checked in the budget's own locked transaction, together with the charge
+ * ({@link AIR_QUALITY_HISTORY_CEILING}), so two worker processes, or the
+ * history beside the nightly fetch, cannot both read room only one of them
+ * gets. A run that reaches a
  * ceiling stops; the nightly discovery picks the account up again, so a long
  * history spreads over several days by construction.
  *
@@ -56,14 +74,16 @@
  *
  * A day is done once its row carries `aqFetchedAt`; done days are never asked
  * for again, and the writes only touch rows still without it (or create the
- * row). Each run stores `{ total, done, checkedAt, complete }` on
+ * row). The days with entries are read once per chain and handed from run
+ * to run in the follow-up's payload ({@link EntryDaysSnapshot}), so a chain
+ * of fifty runs scans the entry tables once, not fifty times. Each run
+ * stores `{ total, done, checkedAt, complete }` on
  * `User.environmentAqHistoryJson`, which the settings card shows as
  * "Backfilling air quality: x of y days".
  */
 import { Prisma } from "@/generated/prisma/client";
 import { prisma, toJson } from "@/lib/db";
 import {
-  airQualityChunkWeight,
   earliestAirQualityDay,
   fetchDailyAirQuality,
   isAirQualityActive,
@@ -73,16 +93,13 @@ import {
   type DailyAirQualityObservation,
 } from "@/lib/environment/open-meteo-air-quality";
 import {
-  archiveRequestWeight,
   fetchDailyEnvironment,
   type DailyEnvironmentObservation,
 } from "@/lib/environment/open-meteo";
 import {
   OPEN_METEO_ACCOUNT_DAY_WINDOW,
-  OPEN_METEO_BUDGET_WINDOWS,
   OpenMeteoBudgetExhaustedError,
-  readOpenMeteoBudgetUsage,
-  type BudgetUsage,
+  type BudgetCeiling,
 } from "@/lib/environment/request-budget";
 import { readLocation, sealLocation } from "@/lib/environment/location-cipher";
 import {
@@ -93,11 +110,11 @@ import {
   inAnyPeriod,
   readTravelOverrides,
   resolveHome,
+  resolveLocationForDay,
   utcDayKey,
-  type HomeLocation,
   type ResolvedLocation,
-  type TravelOverride,
 } from "@/lib/environment/service";
+import { isModuleEnabled } from "@/lib/modules/gate";
 import { shiftDateKey } from "@/lib/tz/format";
 import { startOfLocalDayKey } from "@/lib/tz/local-day";
 
@@ -115,6 +132,11 @@ export const AIR_QUALITY_HISTORY_ACCOUNT_DAY_CALLS = Math.floor(
 );
 /** The history's share of each instance-wide window. */
 export const AIR_QUALITY_HISTORY_INSTANCE_SHARE = 0.5;
+/** Both ceilings, as every history request hands them to the budget. */
+export const AIR_QUALITY_HISTORY_CEILING: BudgetCeiling = {
+  instanceShare: AIR_QUALITY_HISTORY_INSTANCE_SHARE,
+  accountDayCalls: AIR_QUALITY_HISTORY_ACCOUNT_DAY_CALLS,
+};
 
 /** One pending day and where it is fetched. */
 export interface HistoryDay {
@@ -159,60 +181,6 @@ export function planHistoryRanges(
   return ranges;
 }
 
-/**
- * The weight of one range in calls: its air-quality request, plus the
- * weather request over the span of its days without a row, when it has any.
- */
-export function historyRangeWeight(
-  range: HistoryRange,
-  missingRowDays: readonly string[],
-): number {
-  const air = airQualityChunkWeight(range.startDate, range.endDate);
-  if (missingRowDays.length === 0) return air;
-  const sorted = [...missingRowDays].sort();
-  return air + archiveRequestWeight(sorted[0], sorted[sorted.length - 1]);
-}
-
-/**
- * Whether a request of `weight` calls fits under the history's ceilings, given
- * what each window already holds. Pure; exported for tests.
- */
-export function historyRequestFits(
-  usage: BudgetUsage,
-  weight: number,
-): boolean {
-  for (const w of OPEN_METEO_BUDGET_WINDOWS) {
-    const ceiling = w.limit * AIR_QUALITY_HISTORY_INSTANCE_SHARE;
-    if ((usage[w.name] ?? 0) + weight > ceiling) return false;
-  }
-  return (
-    (usage["account-day"] ?? 0) + weight <=
-    AIR_QUALITY_HISTORY_ACCOUNT_DAY_CALLS
-  );
-}
-
-/**
- * Where a day without a row is placed: the period that covers it, else the
- * home from `homeSince` on, or on every day when no `homeSince` is stored
- * (see the header). Null for a day before the home with no period. Pure;
- * exported for tests.
- */
-export function resolveHistoryLocation(
-  day: string,
-  home: HomeLocation | null,
-  travels: readonly TravelOverride[],
-): ResolvedLocation | null {
-  for (const t of travels) {
-    if (day >= t.startDate && day <= t.endDate) {
-      return { lat: t.lat, lon: t.lon, label: t.label, source: "TRAVEL" };
-    }
-  }
-  if (home && (home.since === null || day >= home.since)) {
-    return { lat: home.lat, lon: home.lon, label: home.label, source: "HOME" };
-  }
-  return null;
-}
-
 /** The stored progress, as the settings card reads it. */
 export interface AirQualityHistoryState {
   version: 1;
@@ -258,6 +226,13 @@ export function readAirQualityHistoryState(
  * mood entry, a taken dose, a symptom or a workout. Distinct in SQL, so a
  * dense record costs a scan, not a transfer. `tz` is a zone the account
  * stored (home or profile), bound as a parameter.
+ *
+ * Measured on Postgres 16 with 4 000 days of readings: 4 000 rows answer in
+ * about 5 ms, 400 000 rows (100 a day) in about 75 ms, almost all of it the
+ * measurement scan and its hash aggregate (`EXPLAIN ANALYZE`: a parallel
+ * sequential scan feeding a HashAggregate, 6.4 MB per worker). The cost
+ * grows with the readings, not with the days, so it is read once per chain
+ * and handed on ({@link EntryDaysSnapshot}), not once per run.
  */
 export async function readEntryDays(
   userId: string,
@@ -301,21 +276,53 @@ export async function readEntryDays(
     .sort();
 }
 
+/**
+ * The days with entries as one run read them, handed to the next run of the
+ * same chain so the entry tables are scanned once per chain. Valid only for
+ * the zone and the cutoff it was read under; a run under another one (the
+ * home moved, or the chain crossed midnight) reads afresh.
+ */
+export interface EntryDaysSnapshot {
+  timezone: string;
+  cutoff: string;
+  days: string[];
+}
+
+/** Tolerant read of a snapshot from a job payload; null for anything else. */
+export function readEntryDaysSnapshot(raw: unknown): EntryDaysSnapshot | null {
+  if (raw === null || typeof raw !== "object") return null;
+  const r = raw as Record<string, unknown>;
+  if (
+    typeof r.timezone !== "string" ||
+    typeof r.cutoff !== "string" ||
+    !Array.isArray(r.days) ||
+    !r.days.every((d) => typeof d === "string")
+  ) {
+    return null;
+  }
+  return { timezone: r.timezone, cutoff: r.cutoff, days: r.days as string[] };
+}
+
 /** What the history still has to do for an account, and how far it is. */
 export interface HistoryWork {
   pending: HistoryDay[];
   total: number;
   done: number;
   timezone: string;
+  /** The entry days this collection used, for the chain's next run. */
+  entryDays: EntryDaysSnapshot;
 }
 
 /**
  * Collect the pending days and the counts. Null when the account is gone or
- * its air quality is off (for the account or the instance).
+ * its air quality is off (for the account or the instance). With `entryDays`
+ * from the chain's previous run under the same zone and cutoff, the entry
+ * tables are not read again.
  */
 export async function collectAirQualityHistory(
   userId: string,
   now: Date = new Date(),
+  entryDays: EntryDaysSnapshot | null = null,
 ): Promise<HistoryWork | null> {
   const user = await prisma.user.findUnique({
     where: { id: userId },
@@ -329,11 +336,23 @@ export async function collectAirQualityHistory(
   const timezone = home?.timezone ?? user.timezone;
   const cutoff = shiftDateKey(utcDayKey(now), -AIR_QUALITY_HISTORY_SETTLE_DAYS);
   if (cutoff < AIR_QUALITY_EARLIEST_DAY) {
-    return { pending: [], total: 0, done: 0, timezone };
+    return {
+      pending: [],
+      total: 0,
+      done: 0,
+      timezone,
+      entryDays: { timezone, cutoff, days: [] },
+    };
   }
 
-  const [entryDays, rows] = await Promise.all([
-    readEntryDays(userId, timezone, AIR_QUALITY_EARLIEST_DAY, cutoff),
+  const reuse =
+    entryDays !== null &&
+    entryDays.timezone === timezone &&
+    entryDays.cutoff === cutoff;
+  const [days, rows] = await Promise.all([
+    reuse
+      ? entryDays.days
+      : readEntryDays(userId, timezone, AIR_QUALITY_EARLIEST_DAY, cutoff),
     prisma.environmentContext.findMany({
       where: { userId, date: { gte: AIR_QUALITY_EARLIEST_DAY, lte: cutoff } },
       select: {
@@ -352,7 +371,7 @@ export async function collectAirQualityHistory(
   const pending: HistoryDay[] = [];
   let total = 0;
   let done = 0;
-  for (const date of entryDays) {
+  for (const date of days) {
     const row = rowByDate.get(date);
     let location: ResolvedLocation | null;
     if (row) {
@@ -366,7 +385,7 @@ export async function collectAirQualityHistory(
     } else if (inAnyPeriod(date, travel.unreadable)) {
       location = null;
     } else {
-      location = resolveHistoryLocation(date, home, travel.overrides);
+      location = resolveLocationForDay(date, home, travel.overrides);
     }
     if (!location) continue;
     // Outside what the source serves at this place: left empty, not counted.
@@ -378,31 +397,38 @@ export async function collectAirQualityHistory(
       pending.push({ date, location, hasRow: row != null });
     }
   }
-  return { pending, total, done, timezone };
-}
-
-/** A weather observation with nothing in it, for a day the archive skipped. */
-function emptyWeather(date: string): DailyEnvironmentObservation {
   return {
-    date,
-    tempMin: null,
-    tempMax: null,
-    tempMean: null,
-    apparentMean: null,
-    apparentMax: null,
-    sunshineSec: null,
-    daylightSec: null,
-    precipSum: null,
-    pressureMean: null,
-    pressureDelta: null,
-    humidityMean: null,
-    cloudMean: null,
-    weatherCode: null,
+    pending,
+    total,
+    done,
+    timezone,
+    entryDays: { timezone, cutoff, days },
   };
 }
 
+/**
+ * Whether the history may still send for the account: the account exists,
+ * its environment module is on, and its air quality is on for the account
+ * and the instance. Read before every range, so switching any of them off
+ * stops a run between two ranges, not only at the next run.
+ */
+async function historyStillActive(userId: string): Promise<boolean> {
+  const user = await prisma.user.findUnique({
+    where: { id: userId },
+    select: { environmentAirQualityEnabled: true },
+  });
+  if (!user || !isAirQualityActive(user.environmentAirQualityEnabled)) {
+    return false;
+  }
+  return isModuleEnabled(userId, "environment");
+}
+
 export interface AirQualityHistoryRunResult {
-  /** `inactive`: the account is gone or its air quality is off. */
+  /**
+   * `inactive`: the account is gone, or its module or air quality is off
+   * (at the start or between two ranges). `error`: the feed refused a
+   * request, which ends the run and its chain.
+   */
   status: "inactive" | "complete" | "progress" | "budget" | "error";
   /** Days whose air quality this run stored. */
   filled: number;
@@ -412,20 +438,30 @@ export interface AirQualityHistoryRunResult {
   done: number;
   /** Days still pending after this run. */
   remaining: number;
+  /** The entry days this run used, for its follow-up; null when inactive. */
+  entryDays: EntryDaysSnapshot | null;
 }
 
 /**
  * One run of the history for an account: up to `maxRanges` ranges, newest
  * first, inside the history's budget ceilings. Stores the progress and says
- * why it stopped.
+ * why it stopped. `entryDays` is the previous run's snapshot in a chain.
  */
 export async function runAirQualityHistory(
   userId: string,
-  opts: { now?: Date; maxRanges?: number } = {},
+  opts: {
+    now?: Date;
+    maxRanges?: number;
+    entryDays?: EntryDaysSnapshot | null;
+  } = {},
 ): Promise<AirQualityHistoryRunResult> {
   const now = opts.now ?? new Date();
   const maxRanges = opts.maxRanges ?? AIR_QUALITY_HISTORY_RANGES_PER_RUN;
-  const work = await collectAirQualityHistory(userId, now);
+  const work = await collectAirQualityHistory(
+    userId,
+    now,
+    opts.entryDays ?? null,
+  );
   if (!work) {
     return {
       status: "inactive",
@@ -434,6 +470,7 @@ export async function runAirQualityHistory(
       total: 0,
       done: 0,
       remaining: 0,
+      entryDays: null,
     };
   }
 
@@ -461,46 +498,23 @@ export async function runAirQualityHistory(
     )
     .sort((a, b) => b.range.endDate.localeCompare(a.range.endDate));
 
+  const budget = { accountId: userId, ceiling: AIR_QUALITY_HISTORY_CEILING };
   let filled = 0;
   let fetches = 0;
-  let stop: "budget" | "error" | null = null;
-  let errors = 0;
+  let stop: "budget" | "error" | "inactive" | null = null;
   let attempted = 0;
   for (const { group, range } of planned) {
     if (attempted >= maxRanges) break;
+    if (!(await historyStillActive(userId))) {
+      stop = "inactive";
+      break;
+    }
     attempted += 1;
     const days = range.days.map((d) => group.byDate.get(d)!);
     const missing = days.filter((d) => !d.hasRow).map((d) => d.date);
-    const usage = await readOpenMeteoBudgetUsage(userId, new Date());
-    if (!historyRequestFits(usage, historyRangeWeight(range, missing))) {
-      stop = "budget";
-      break;
-    }
-
-    const air = await fetchDailyAirQuality(
-      {
-        lat: group.lat,
-        lon: group.lon,
-        timezone: work.timezone,
-        startDate: range.startDate,
-        endDate: range.endDate,
-      },
-      { accountId: userId },
-    );
-    if (air.stopped === "budget") {
-      stop = "budget";
-      break;
-    }
-    if (air.stopped === "error") {
-      errors += 1;
-      continue;
-    }
-    fetches += 1;
-    const airByDay = new Map<string, DailyAirQualityObservation>(
-      air.days.map((d) => [d.date, d]),
-    );
-    const airFor = (date: string) => airByDay.get(date) ?? uncoverableDay(date);
 
+    // The weather first, so a refused or failed archive request costs no
+    // air-quality call.
     let weather: Map<string, DailyEnvironmentObservation> | null = null;
     if (missing.length > 0) {
       try {
@@ -512,55 +526,88 @@ export async function runAirQualityHistory(
             startDate: missing[0],
             endDate: missing[missing.length - 1],
           },
-          { accountId: userId },
+          budget,
         );
         fetches += 1;
         weather = new Map(observations.map((o) => [o.date, o]));
       } catch (err) {
-        if (err instanceof OpenMeteoBudgetExhaustedError) {
-          stop = "budget";
-        } else {
-          errors += 1;
-        }
-        // The days with a row are stored below; those without one stay
-        // pending until the weather can be fetched with them.
+        stop =
+          err instanceof OpenMeteoBudgetExhaustedError ? "budget" : "error";
+        if (stop === "error") fetches += 1;
+        break;
       }
     }
 
+    const air = await fetchDailyAirQuality(
+      {
+        lat: group.lat,
+        lon: group.lon,
+        timezone: work.timezone,
+        startDate: range.startDate,
+        endDate: range.endDate,
+      },
+      budget,
+    );
+    if (air.stopped !== "budget") fetches += 1;
+    const airByDay = new Map<string, DailyAirQualityObservation>(
+      air.days.map((d) => [d.date, d]),
+    );
+    // A day the feed did not answer after a full fetch is one it cannot
+    // cover; after a stopped fetch it is simply not fetched yet.
+    const airFor = (date: string): DailyAirQualityObservation | null =>
+      airByDay.get(date) ??
+      (air.stopped === null ? uncoverableDay(date) : null);
+
     const fetchedAt = new Date();
     const ops: Prisma.PrismaPromise<unknown>[] = [];
+    const fillsAir: boolean[] = [];
     for (const day of days) {
+      const dayAir = airFor(day.date);
       if (day.hasRow) {
+        if (!dayAir) continue;
         ops.push(
           prisma.environmentContext.updateMany({
             // Still unfetched, so a weather rewrite that landed meanwhile
             // (with its own air quality) is not overwritten.
             where: { userId, date: day.date, aqFetchedAt: null },
-            data: airQualityColumns(airFor(day.date), fetchedAt),
+            data: airQualityColumns(dayAir, fetchedAt),
           }),
         );
-      } else if (weather) {
-        ops.push(
-          buildUpsert(
-            userId,
-            day.location,
-            sealLocation(day.location),
-            weather.get(day.date) ?? emptyWeather(day.date),
-            { active: true, day: airFor(day.date), now: fetchedAt },
-          ),
-        );
+        fillsAir.push(true);
+        continue;
       }
+      // A day the archive answer left out gets no row: it stays pending
+      // instead of carrying empty weather nothing would fetch again.
+      const observation = weather?.get(day.date);
+      if (!observation) continue;
+      // Without its air quality (the air request stopped), the weather row
+      // is still stored: it was paid for, and the next run then asks for
+      // the air quality alone.
+      ops.push(
+        buildUpsert(
+          userId,
+          day.location,
+          sealLocation(day.location),
+          observation,
+          { active: true, day: dayAir, now: fetchedAt },
+        ),
+      );
+      fillsAir.push(dayAir !== null);
     }
     if (ops.length > 0) {
       const results = await prisma.$transaction(ops);
-      for (const r of results) {
+      results.forEach((r, i) => {
+        if (!fillsAir[i]) return;
         filled +=
           r && typeof r === "object" && "count" in r
             ? Number((r as { count: number }).count)
             : 1;
-      }
+      });
+    }
+    if (air.stopped) {
+      stop = air.stopped;
+      break;
     }
-    if (stop) break;
   }
 
   const done = Math.min(work.total, work.done + filled);
@@ -578,12 +625,14 @@ export async function runAirQualityHistory(
   });
 
   const status: AirQualityHistoryRunResult["status"] =
-    remaining === 0
-      ? "complete"
-      : stop === "budget"
-        ? "budget"
-        : errors > 0 && filled === 0
-          ? "error"
-          : "progress";
-  return { status, filled, fetches, total: work.total, done, remaining };
+    remaining === 0 ? "complete" : (stop ?? "progress");
+  return {
+    status,
+    filled,
+    fetches,
+    total: work.total,
+    done,
+    remaining,
+    entryDays: work.entryDays,
+  };
 }
diff --git a/src/lib/environment/open-meteo-air-quality.ts b/src/lib/environment/open-meteo-air-quality.ts
index 85d44b373..d782b3f20 100644
--- a/src/lib/environment/open-meteo-air-quality.ts
+++ b/src/lib/environment/open-meteo-air-quality.ts
@@ -72,6 +72,7 @@ import { enumerateDayCount } from "@/lib/environment/day-span";
 import {
   openMeteoCallWeight,
   reserveOpenMeteoCalls,
+  type BudgetCeiling,
 } from "@/lib/environment/request-budget";
 
 /** Hosted default; override with `OPENMETEO_AIR_QUALITY_URL` (self-host). */
@@ -395,7 +396,7 @@ export async function fetchDailyAirQuality(
     startDate: string;
     endDate: string;
   },
-  budget: { accountId?: string } = {},
+  budget: { accountId?: string; ceiling?: BudgetCeiling } = {},
 ): Promise<AirQualityFetchResult> {
   const days: DailyAirQualityObservation[] = [];
   // Days before the feed's first day at this location are answered here,
@@ -415,7 +416,9 @@ export async function fetchDailyAirQuality(
   for (const chunk of chunks) {
     const variables = variablesForChunk(chunk.endDate);
     const weight = airQualityChunkWeight(chunk.startDate, chunk.endDate);
-    if (!(await reserveOpenMeteoCalls(weight, budget.accountId))) {
+    if (
+      !(await reserveOpenMeteoCalls(weight, budget.accountId, budget.ceiling))
+    ) {
       return { days, stopped: "budget" };
     }
     try {
diff --git a/src/lib/environment/open-meteo.ts b/src/lib/environment/open-meteo.ts
index ed3245e14..a0f8e7e43 100644
--- a/src/lib/environment/open-meteo.ts
+++ b/src/lib/environment/open-meteo.ts
@@ -26,6 +26,7 @@ import {
   OpenMeteoBudgetExhaustedError,
   openMeteoCallWeight,
   reserveOpenMeteoCalls,
+  type BudgetCeiling,
 } from "@/lib/environment/request-budget";
 
 /** Hosted archive default; override with `OPENMETEO_BASE_URL` (self-host). */
@@ -278,10 +279,12 @@ export async function fetchDailyEnvironment(
     startDate: string;
     endDate: string;
   },
-  budget: { accountId?: string } = {},
+  budget: { accountId?: string; ceiling?: BudgetCeiling } = {},
 ): Promise<DailyEnvironmentObservation[]> {
   const weight = archiveRequestWeight(args.startDate, args.endDate);
-  if (!(await reserveOpenMeteoCalls(weight, budget.accountId))) {
+  if (
+    !(await reserveOpenMeteoCalls(weight, budget.accountId, budget.ceiling))
+  ) {
     throw new OpenMeteoBudgetExhaustedError();
   }
   const url = new URL(`${ARCHIVE_BASE_URL}/v1/archive`);
diff --git a/src/lib/environment/request-budget.ts b/src/lib/environment/request-budget.ts
index 05f6d46fa..220f8d335 100644
--- a/src/lib/environment/request-budget.ts
+++ b/src/lib/environment/request-budget.ts
@@ -114,16 +114,54 @@ export function admitWeight(
   return { admitted: true, next };
 }
 
+/**
+ * A lower ceiling a caller holds itself to inside the budget: a share of each
+ * instance window, and a number of calls inside the account's daily share.
+ * The air-quality history backfill uses one so the nightly fetch and
+ * on-demand requests keep their room. The ceiling is checked against
+ * everything the windows hold, not only against the caller's own calls, and
+ * the request is charged to the windows as usual.
+ */
+export interface BudgetCeiling {
+  /** Share of each instance window the request may fill up to (0..1). */
+  instanceShare: number;
+  /** Calls the account's daily window may hold after the request. */
+  accountDayCalls: number;
+}
+
+/**
+ * The windows with their limits lowered to `ceiling`. Only the limits
+ * change, so the buckets written are the same as without a ceiling. Pure;
+ * exported for tests.
+ */
+export function windowsUnderCeiling(
+  windows: readonly BudgetWindow[],
+  ceiling: BudgetCeiling | undefined,
+): readonly BudgetWindow[] {
+  if (!ceiling) return windows;
+  return windows.map((w) => ({
+    ...w,
+    limit:
+      w.name === "account-day"
+        ? Math.min(w.limit, ceiling.accountDayCalls)
+        : w.limit * ceiling.instanceShare,
+  }));
+}
+
 /**
  * Ask the budget for one request of `weight` calls. Returns true and charges
  * every window when it fits, false (charging nothing) when any window is
  * full. With `accountId`, the account's own daily share is checked and
  * charged as well (`OPEN_METEO_ACCOUNT_DAY_SHARE`); requests made for no
  * particular account (the geocoder) are bound by the instance windows only.
+ * With `ceiling`, the request is admitted only under that lower ceiling, and
+ * the check runs under the same lock as the charge, so two processes cannot
+ * both read room that only one of them gets.
  */
 export async function reserveOpenMeteoCalls(
   weight: number,
   accountId?: string,
+  ceiling?: BudgetCeiling,
 ): Promise<boolean> {
   const weightCenti = Math.max(1, Math.ceil(weight * CENTI));
   const windows: readonly BudgetWindow[] = accountId
@@ -150,7 +188,12 @@ export async function reserveOpenMeteoCalls(
       const name = nameOfKey.get(row.key);
       if (name) buckets.set(name, { count: row.count, resetAt: row.resetAt });
     }
-    const decision = admitWeight(buckets, weightCenti, new Date(), windows);
+    const decision = admitWeight(
+      buckets,
+      weightCenti,
+      new Date(),
+      windowsUnderCeiling(windows, ceiling),
+    );
     if (!decision.admitted) return false;
     for (const [name, bucket] of decision.next) {
       const key = keyOf(name);
@@ -171,39 +214,3 @@ export class OpenMeteoBudgetExhaustedError extends Error {
     this.name = "OpenMeteoBudgetExhaustedError";
   }
 }
-
-/** Calls already charged to each live window, by window name. */
-export type BudgetUsage = Partial<Record<BudgetWindow["name"], number>>;
-
-/**
- * Read how much of each window is in use, in calls, without charging
- * anything. A window never written or already reset reads as absent (zero).
- * With `accountId` the account's daily share is read as well. Used by the
- * air-quality history backfill, which holds itself under a ceiling of its own
- * so the nightly fetch and on-demand requests keep their room.
- */
-export async function readOpenMeteoBudgetUsage(
-  accountId?: string,
-  now: Date = new Date(),
-): Promise<BudgetUsage> {
-  const keys = new Map<string, BudgetWindow["name"]>(
-    OPEN_METEO_BUDGET_WINDOWS.map((w) => [
-      `${BUCKET_PREFIX}:${w.name}`,
-      w.name,
-    ]),
-  );
-  if (accountId) {
-    keys.set(`${BUCKET_PREFIX}:account:${accountId}:day`, "account-day");
-  }
-  const rows = await prisma.rateLimit.findMany({
-    where: { key: { in: [...keys.keys()] } },
-    select: { key: true, count: true, resetAt: true },
-  });
-  const usage: BudgetUsage = {};
-  for (const row of rows) {
-    const name = keys.get(row.key);
-    if (!name || row.resetAt.getTime() <= now.getTime()) continue;
-    usage[name] = row.count / CENTI;
-  }
-  return usage;
-}
diff --git a/src/lib/jobs/environment-air-quality-history.ts b/src/lib/jobs/environment-air-quality-history.ts
index f63423b19..ad6acea4a 100644
--- a/src/lib/jobs/environment-air-quality-history.ts
+++ b/src/lib/jobs/environment-air-quality-history.ts
@@ -16,8 +16,16 @@
  * ceiling stopped it, it sends its own follow-up half a minute later. A run
  * the budget stopped sends none: the next nightly discovery resumes it, which
  * is what spreads a long history over several days. The module gate and the
- * air-quality switches are re-read on every run, so switching either off
- * ends the chain.
+ * air-quality switches are re-read before every range, so switching either
+ * off ends the run and the chain.
+ *
+ * A run the feed refused a request in (429, 5xx, network) ends with status
+ * `error`: it reports a failed job and sends no follow-up, and the sends
+ * carry `retryLimit: 0`, so pg-boss does not retry it straight into the
+ * same refusal either. The next nightly discovery tries again.
+ *
+ * The follow-up carries the days with entries the run read
+ * (`entryDays`), so a chain scans the entry tables once.
  *
  * The queue name MUST be registered in `allQueues` in
  * `src/lib/jobs/reminder/register-maintenance.ts`, or the sends silently
@@ -37,7 +45,9 @@ import {
 import { isAirQualityOperatorDisabled } from "@/lib/environment/open-meteo-air-quality";
 import {
   readAirQualityHistoryState,
+  readEntryDaysSnapshot,
   runAirQualityHistory,
+  type EntryDaysSnapshot,
 } from "@/lib/environment/air-quality-history";
 import { workerLog } from "./reminder/shared";
 
@@ -59,8 +69,16 @@ export interface EnvironmentAqHistoryPayload {
   /** Absent on the discovery tick. */
   userId?: string;
   continuation?: number;
+  /** The previous run's entry days, on a follow-up only. */
+  entryDays?: EntryDaysSnapshot;
 }
 
+/**
+ * No pg-boss retry: a run fails when the feed refused it, and an immediate
+ * retry would only ask the same feed again. The next discovery is the retry.
+ */
+const AQ_HISTORY_SEND_OPTIONS = { retryLimit: 0 } as const;
+
 function singletonKey(userId: string): string {
   return `environment-aq-history:${userId}`;
 }
@@ -80,6 +98,7 @@ export async function enqueueAirQualityHistory(
     ENVIRONMENT_AQ_HISTORY_QUEUE,
     { userId } satisfies EnvironmentAqHistoryPayload,
     {
+      ...AQ_HISTORY_SEND_OPTIONS,
       singletonKey: singletonKey(userId),
       ...(startAfterSeconds > 0 ? { startAfter: startAfterSeconds } : {}),
     },
@@ -149,6 +168,7 @@ export async function discoverAirQualityHistory(
       ENVIRONMENT_AQ_HISTORY_QUEUE,
       { userId: candidate.id } satisfies EnvironmentAqHistoryPayload,
       {
+        ...AQ_HISTORY_SEND_OPTIONS,
         singletonKey: singletonKey(candidate.id),
         ...(startAfterSeconds > 0 ? { startAfter: startAfterSeconds } : {}),
       },
@@ -203,7 +223,9 @@ export async function handleEnvironmentAqHistory(
     return jobDone({ skipped: "environment_module_disabled" });
   }
 
-  const result = await runAirQualityHistory(userId);
+  const result = await runAirQualityHistory(userId, {
+    entryDays: readEntryDaysSnapshot(payload.entryDays),
+  });
   const continuation = payload.continuation ?? 0;
   let continued = false;
   if (
@@ -216,8 +238,10 @@ export async function handleEnvironmentAqHistory(
       {
         userId,
         continuation: continuation + 1,
+        ...(result.entryDays ? { entryDays: result.entryDays } : {}),
       } satisfies EnvironmentAqHistoryPayload,
       {
+        ...AQ_HISTORY_SEND_OPTIONS,
         singletonKey: singletonKey(userId),
         startAfter: AQ_HISTORY_CONTINUATION_DELAY_SECONDS,
       },
@@ -228,13 +252,18 @@ export async function handleEnvironmentAqHistory(
     "info",
     `[environment-aq-history] user=${userId} status=${result.status} filled=${result.filled} done=${result.done}/${result.total} fetches=${result.fetches}${continued ? " continued" : ""}`,
   );
-  // Every range failed at the feed: say so, so the failing-jobs card sees a
+  // The feed refused a request: say so, so the failing-jobs card sees a
   // feed that keeps refusing. A budget stop is not a failure: nothing was
   // sent past the ceiling, and the next discovery resumes where it stopped.
   if (result.status === "error") {
-    return jobFailed("air-quality history: every range failed", undefined, {
-      fetches: result.fetches,
-    });
+    return jobFailed(
+      "air-quality history: the feed refused a request",
+      undefined,
+      {
+        fetches: result.fetches,
+        days_stored: result.filled,
+      },
+    );
   }
   return jobDone({
     outcome: result.status,
diff --git a/tests/integration/environment-air-quality-history.test.ts b/tests/integration/environment-air-quality-history.test.ts
index b71bf55ae..249ecd696 100644
--- a/tests/integration/environment-air-quality-history.test.ts
+++ b/tests/integration/environment-air-quality-history.test.ts
@@ -21,8 +21,10 @@ import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 
 import {
   AIR_QUALITY_HISTORY_ACCOUNT_DAY_CALLS,
+  AIR_QUALITY_HISTORY_CEILING,
   runAirQualityHistory,
 } from "@/lib/environment/air-quality-history";
+import { reserveOpenMeteoCalls } from "@/lib/environment/request-budget";
 import { openLocation, sealLocation } from "@/lib/environment/location-cipher";
 import { handleEnvironmentAqHistory } from "@/lib/jobs/environment-air-quality-history";
 import { getPrismaClient, truncateAllTables } from "./setup";
@@ -49,8 +51,19 @@ function daysBetween(start: string, end: string): string[] {
   return out;
 }
 
+interface StubOptions {
+  /** HTTP status the archive answers with instead of data. */
+  archiveStatus?: number;
+  /** HTTP status the air-quality API answers with instead of data. */
+  airStatus?: number;
+  /** Days the archive leaves out of its answer. */
+  omitArchiveDays?: readonly string[];
+  /** Runs before every air-quality answer. */
+  onAir?: () => Promise<void>;
+}
+
 /** Answers both feeds with a full day of values for every requested day. */
-function openMeteoStub() {
+function openMeteoStub(opts: StubOptions = {}) {
   return vi.fn(async (input: unknown) => {
     const url = new URL(String(input));
     const days = daysBetween(
@@ -58,6 +71,8 @@ function openMeteoStub() {
       url.searchParams.get("end_date")!,
     );
     if (url.pathname === "/v1/air-quality") {
+      await opts.onAir?.();
+      if (opts.airStatus) return new Response("", { status: opts.airStatus });
       const variables = url.searchParams.get("hourly")!.split(",");
       const time = days.flatMap((d) =>
         Array.from(
@@ -69,11 +84,15 @@ function openMeteoStub() {
       for (const v of variables) hourly[v] = time.map(() => 12);
       return Response.json({ hourly });
     }
-    const daily: Record<string, unknown> = { time: days };
-    for (const field of url.searchParams.get("daily")!.split(",")) {
-      daily[field] = days.map(() => 5);
+    if (opts.archiveStatus) {
+      return new Response("", { status: opts.archiveStatus });
     }
-    const time = days.flatMap((d) =>
+    const answered = days.filter((d) => !opts.omitArchiveDays?.includes(d));
+    const daily: Record<string, unknown> = { time: answered };
+    for (const field of url.searchParams.get("daily")!.split(",")) {
+      daily[field] = answered.map(() => 5);
+    }
+    const time = answered.flatMap((d) =>
       Array.from(
         { length: 24 },
         (_, h) => `${d}T${String(h).padStart(2, "0")}:00`,
@@ -194,6 +213,22 @@ function requests() {
   return fetchSpy.mock.calls.map(([input]) => new URL(String(input)));
 }
 
+function useStub(opts: StubOptions) {
+  fetchSpy = openMeteoStub(opts);
+  vi.stubGlobal("fetch", fetchSpy);
+}
+
+/** `[path, start_date]` of every request sent, in order. */
+function sentRanges() {
+  return requests().map((u) => [u.pathname, u.searchParams.get("start_date")]);
+}
+
+async function rowOn(day: string) {
+  return getPrismaClient().environmentContext.findUnique({
+    where: { userId_date: { userId: OWNER, date: day } },
+  });
+}
+
 describe("air-quality history backfill", () => {
   it("fills every past day with entries the source reaches, once", async () => {
     const prisma = getPrismaClient();
@@ -366,3 +401,189 @@ describe("air-quality history backfill", () => {
     expect(sends).toEqual([]);
   });
 });
+
+describe("air-quality history: placing, failing and stopping", () => {
+  it("places no day at a home stored without an effective date, as the nightly fetch does", async () => {
+    await getPrismaClient().user.update({
+      where: { id: OWNER },
+      data: { homeSince: null },
+    });
+    const result = await runAirQualityHistory(OWNER, { now: NOW });
+    // The two 2020 trip days, the 2024 trip day, the day with a row and the
+    // day already done; the home day without a row is not placed anywhere.
+    expect(result).toMatchObject({ status: "complete", total: 5, done: 5 });
+    expect(await rowOn("2025-09-10")).toBeNull();
+    expect(sentRanges().map(([, start]) => start)).not.toContain("2025-09-10");
+  });
+
+  it("stops at the first refused archive request and sends no air-quality request for it", async () => {
+    useStub({ archiveStatus: 503 });
+    const result = await runAirQualityHistory(OWNER, { now: NOW });
+    expect(result).toMatchObject({ status: "error", filled: 0, fetches: 1 });
+    expect(sentRanges()).toEqual([["/v1/archive", "2025-09-10"]]);
+  });
+
+  it("stops at the first refused air-quality request and keeps the weather it already paid for", async () => {
+    useStub({ airStatus: 429 });
+    const result = await runAirQualityHistory(OWNER, { now: NOW });
+    expect(result).toMatchObject({ status: "error", filled: 0, fetches: 2 });
+    expect(sentRanges()).toEqual([
+      ["/v1/archive", "2025-09-10"],
+      ["/v1/air-quality", "2025-09-10"],
+    ]);
+    // The weather row is stored, without air quality.
+    expect(await rowOn("2025-09-10")).toMatchObject({
+      tempMax: 5,
+      pm25Mean: null,
+      aqFetchedAt: null,
+    });
+
+    // The next run asks for that day's air quality only.
+    useStub({});
+    const next = await runAirQualityHistory(OWNER, { now: NOW });
+    expect(next.status).toBe("complete");
+    expect(sentRanges().filter(([, start]) => start === "2025-09-10")).toEqual([
+      ["/v1/air-quality", "2025-09-10"],
+    ]);
+    expect(await rowOn("2025-09-10")).toMatchObject({
+      tempMax: 5,
+      pm25Mean: 12,
+    });
+  });
+
+  it("sends no follow-up and no retry after a refused request", async () => {
+    useStub({ archiveStatus: 503 });
+    const sends: Array<{ data: unknown; options: unknown }> = [];
+    const boss = {
+      send: vi.fn(async (_name: string, data: unknown, options: unknown) => {
+        sends.push({ data, options });
+        return "job-id";
+      }),
+    };
+    const outcome = await handleEnvironmentAqHistory(boss as never, {
+      userId: OWNER,
+    });
+    expect(outcome.ok).toBe(false);
+    expect(sends).toEqual([]);
+  });
+
+  it("creates no row for a day the archive answer leaves out", async () => {
+    useStub({ omitArchiveDays: ["2020-03-05"] });
+    const result = await runAirQualityHistory(OWNER, { now: NOW });
+    expect(result).toMatchObject({ status: "progress", remaining: 1 });
+    expect(await rowOn("2020-03-05")).toBeNull();
+    expect(await rowOn("2020-03-01")).toMatchObject({ pm25Mean: 12 });
+  });
+
+  it.each([
+    [
+      "the account's air quality",
+      () =>
+        getPrismaClient()
+          .user.update({
+            where: { id: OWNER },
+            data: { environmentAirQualityEnabled: false },
+          })
+          .then(() => undefined),
+    ],
+    [
+      "the environment module",
+      () =>
+        getPrismaClient()
+          .user.update({
+            where: { id: OWNER },
+            data: { modulePreferencesJson: { environment: false } },
+          })
+          .then(() => undefined),
+    ],
+    [
+      "the operator switch",
+      async () => {
+        vi.stubEnv("ENVIRONMENT_AIR_QUALITY_DISABLED", "true");
+      },
+    ],
+  ])("stops between two ranges once %s is switched off", async (_, off) => {
+    let first = true;
+    useStub({
+      onAir: async () => {
+        if (first) await off();
+        first = false;
+      },
+    });
+    const result = await runAirQualityHistory(OWNER, { now: NOW });
+    expect(result.status).toBe("inactive");
+    expect(
+      requests().filter((u) => u.pathname === "/v1/air-quality"),
+    ).toHaveLength(1);
+  });
+
+  it("holds the history's ceiling under concurrent reservations", async () => {
+    const prisma = getPrismaClient();
+    const key = `open-meteo-budget:account:${OWNER}:day`;
+    await prisma.rateLimit.create({
+      data: {
+        key,
+        count: (AIR_QUALITY_HISTORY_ACCOUNT_DAY_CALLS - 1) * 100,
+        resetAt: new Date(Date.now() + 3_600_000),
+      },
+    });
+    const admitted = await Promise.all(
+      Array.from({ length: 6 }, () =>
+        reserveOpenMeteoCalls(0.5, OWNER, AIR_QUALITY_HISTORY_CEILING),
+      ),
+    );
+    expect(admitted.filter(Boolean)).toHaveLength(2);
+    const bucket = await prisma.rateLimit.findUniqueOrThrow({ where: { key } });
+    expect(bucket.count).toBe(AIR_QUALITY_HISTORY_ACCOUNT_DAY_CALLS * 100);
+  });
+
+  it("reads the days with entries once per chain and hands them to the follow-up", async () => {
+    // Nine more home days, each more than two weeks apart: more ranges than
+    // one run works through, so the run sends a follow-up.
+    for (let i = 0; i < 9; i++) {
+      await measurementOn(
+        new Date(Date.parse("2025-01-10T00:00:00Z") + i * 20 * 86_400_000)
+          .toISOString()
+          .slice(0, 10),
+      );
+    }
+    const sends: Array<{ data: Record<string, unknown>; options: unknown }> =
+      [];
+    const boss = {
+      send: vi.fn(
+        async (
+          _name: string,
+          data: Record<string, unknown>,
+          options: unknown,
+        ) => {
+          sends.push({ data, options });
+          return "job-id";
+        },
+      ),
+    };
+    const outcome = await handleEnvironmentAqHistory(boss as never, {
+      userId: OWNER,
+    });
+    expect(outcome.ok).toBe(true);
+    expect(sends).toHaveLength(1);
+    const followUp = sends[0]!.data as {
+      userId: string;
+      continuation: number;
+      entryDays: { timezone: string; cutoff: string; days: string[] };
+    };
+    expect(followUp.entryDays.timezone).toBe("Europe/Berlin");
+    // A failed run is not retried straight into the same refusal.
+    expect(sends[0]!.options).toMatchObject({ retryLimit: 0 });
+    expect(followUp.entryDays.days).toContain("2025-01-10");
+
+    // An entry added after the chain read its days is left to the next
+    // chain: the follow-up does not scan the entry tables again.
+    await measurementOn("2025-11-20");
+    fetchSpy.mockClear();
+    await handleEnvironmentAqHistory(boss as never, followUp);
+    expect(await rowOn("2025-11-20")).toBeNull();
+    // A fresh chain reads it.
+    const fresh = await runAirQualityHistory(OWNER);
+    expect(fresh.entryDays!.days).toContain("2025-11-20");
+  });
+});