Cache versioned habit history and load visible calendar ranges

src/App.test.tsx

@@ -326,6 +326,34 @@ describe("homepage", () => {
     expect((await f.json("/today")).completed).toBe(2);
   });
 
+  test("focus retains unchanged calendars, detects remote historical edits and loads expanded history on demand", async () => {
+    const f = connectAccount();
+    const reading = await f.json("/habits", "POST", { name: "Reading", method: "manual" }, 201);
+    await f.json("/habits", "POST", { name: "Walking", method: "manual" }, 201);
+    await render("/");
+    const calendarRequests = () => fetchMock.mock.calls.map(([url]) => String(url)).filter(url => url.includes("/calendar?"));
+    expect(calendarRequests()).toHaveLength(2);
+    expect(calendarRequests()[0]).toContain("from=2026-07-01");
+    expect(calendarRequests()[0]).toContain("compact=true");
+    fetchMock.mockClear();
+    await act(async () => dom.dispatchEvent(new dom.Event("focus")));
+    expect(calendarRequests()).toHaveLength(0);
+    await f.json(`/habits/${reading.id}/days/2026-09-04/progress`, "PUT", { done: true });
+    await act(async () => dom.dispatchEvent(new dom.Event("focus")));
+    expect(calendarRequests()).toHaveLength(1);
+    expect(calendarRequests()[0]).toContain(reading.id);
+    const history = container.querySelector(`#history-${reading.id}`)!;
+    fetchMock.mockClear();
+    await act(async () => history.querySelector<HTMLButtonElement>('[aria-label="12 months"]')!.click());
+    expect(calendarRequests()).toHaveLength(1);
+    expect(calendarRequests()[0]).toContain("from=2025-10-01");
+    expect(history.querySelectorAll(".ds-day")).toHaveLength(365);
+    fetchMock.mockClear();
+    await act(async () => history.querySelector<HTMLButtonElement>('[aria-label="3 months"]')!.click());
+    expect(calendarRequests()).toHaveLength(0);
+    expect(history.querySelectorAll(".ds-day")).toHaveLength(92);
+  });
+
   test("a pending counter save leaves other habits usable and refreshes only its history", async () => {
     const f = connectAccount();
     const water = await f.json("/habits", "POST", { name: "Water", method: "count", target: 8, unit: "glasses" }, 201);

src/components/ArchivedHabits.tsx

@@ -71,7 +71,7 @@ export function ArchivedHabits({ date, revision, onChanged, onExpired, onClose }
             <Button variant="text" disabled={busy || loading} aria-label={`Delete permanently ${habit.name}`} aria-haspopup="dialog" onClick={() => { setDeleteError(""); setDeleting(habit); }}><Trash2 size={16} aria-hidden="true" />Delete permanently</Button>
           </div>
         </header>
-        {selected === habit.habitId && <div className="ds-record-detail" id={`archive-history-${habit.habitId}`}><HabitHistory calendarOnly habit={habit} date={date} revision={revision + attempt} disabled={busy || loading} onExpired={onExpired} onHistorySaved={() => setAttempt(value => value + 1)} /></div>}
+        {selected === habit.habitId && <div className="ds-record-detail" id={`archive-history-${habit.habitId}`}><HabitHistory calendarOnly habit={habit} date={date} revision={habit.calendarRevision ?? revision + attempt} disabled={busy || loading} onExpired={onExpired} onHistorySaved={() => setAttempt(value => value + 1)} /></div>}
       </article>)}
     </div>
     {deleting && <Modal id="delete-archived-habit" size="compact" eyebrow="PERMANENT DELETION" title="Delete this habit?" description={`“${deleting.name ?? "Habit"}” and all its check-ins, tasks, and progress history will be permanently deleted. It will be removed from combined charts; charts with no remaining habits will also be deleted. This cannot be undone.`} busy={busy} initialFocus="[data-cancel-delete]" returnFocus={() => archiveFocus.current} onClose={() => setDeleting(null)}>

src/components/CalendarCache.test.ts

@@ -0,0 +1,27 @@
+import { afterAll, afterEach, expect, spyOn, test } from "bun:test";
+import { CalendarCache } from "./CalendarCache";
+const fetchSpy = spyOn(globalThis, "fetch");
+afterEach(() => fetchSpy.mockReset());
+afterAll(() => fetchSpy.mockRestore());
+const range = { from: "2026-07-01", to: "2026-09-30" };
+test("calendar cache shares in-flight reads, retains wider history and invalidates changed versions", async () => {
+  fetchSpy.mockImplementation(async () => Response.json({ from: range.from, to: range.to, days: [{ date: "2026-07-01" }, { date: "2026-09-01" }] }));
+  const cache = new CalendarCache();
+  await Promise.all([cache.load("habit", "v1", range), cache.load("habit", "v1", range)]);
+  expect(fetchSpy).toHaveBeenCalledTimes(1);
+  expect(String(fetchSpy.mock.calls[0]![0])).toContain("compact=true");
+  const subset = await cache.load("habit", "v1", { from: "2026-09-01", to: range.to });
+  expect(subset.days).toHaveLength(1);
+  expect(fetchSpy).toHaveBeenCalledTimes(1);
+  await cache.load("habit", "v2", range);
+  expect(fetchSpy).toHaveBeenCalledTimes(2);
+  await new CalendarCache().load("habit", "v2", range);
+  expect(fetchSpy).toHaveBeenCalledTimes(3);
+});
+test("a failed history request can be retried without retaining a rejected cache entry", async () => {
+  fetchSpy.mockRejectedValueOnce(new Error("offline")).mockResolvedValue(Response.json({ ...range, days: [] }));
+  const cache = new CalendarCache();
+  await expect(cache.load("habit", "v1", range)).rejects.toThrow("offline");
+  await expect(cache.load("habit", "v1", range)).resolves.toMatchObject({ days: [] });
+  expect(fetchSpy).toHaveBeenCalledTimes(2);
+});

src/components/CalendarCache.tsx

@@ -0,0 +1,34 @@
+import { createContext, useContext, useRef, type ReactNode } from "react";
+import type { CalendarResponse } from "../shared/calendar";
+import { habitRequest } from "../lib/dashboard";
+
+type Range = { from: string; to: string };
+type Entry = Range & { version: string; value: Promise<CalendarResponse> };
+/** Account-scoped, bounded cache; never survives signing out or changing accounts. */
+export class CalendarCache {
+  private entries = new Map<string, Entry[]>();
+  load(habitId: string, version: string, range: Range) {
+    const entries = (this.entries.get(habitId) ?? []).filter(entry => entry.version === version);
+    const cached = entries.find(entry => entry.from <= range.from && entry.to >= range.to);
+    if (cached) return cached.value.then(value => ({ ...value, ...range, days: value.days.filter(day => day.date >= range.from && day.date <= range.to) }));
+    const entry: Entry = { ...range, version, value: habitRequest<CalendarResponse>(`/habits/${habitId}/calendar?${new URLSearchParams({ ...range, compact: "true" })}`) };
+    entries.push(entry);
+    this.entries.delete(habitId);
+    this.entries.set(habitId, entries.slice(-8));
+    if (this.entries.size > 100) this.entries.delete(this.entries.keys().next().value!);
+    entry.value.catch(() => { const current = this.entries.get(habitId); if (current) this.entries.set(habitId, current.filter(item => item !== entry)); });
+    return entry.value;
+  }
+}
+const Context = createContext<CalendarCache | null>(null);
+export function CalendarCacheProvider({ children }: { children: ReactNode }) {
+  const cache = useRef<CalendarCache | null>(null);
+  cache.current ??= new CalendarCache();
+  return <Context.Provider value={cache.current}>{children}</Context.Provider>;
+}
+export function useCalendarCache() {
+  const shared = useContext(Context);
+  const local = useRef<CalendarCache | null>(null);
+  local.current ??= new CalendarCache();
+  return shared ?? local.current;
+}

src/components/HabitHistory.tsx

@@ -1,3 +1,4 @@
+import { useCalendarCache } from "./CalendarCache";
 import { Modal } from "./design-system/Modal";
 import { Pencil } from "lucide-react";
 import { useEffect, useRef, useState, type ReactNode } from "react";
@@ -40,6 +41,10 @@ export function HabitHistory({
   onHistorySaved?: () => void;
   calendarOnly?: boolean;
 }) {
+  const cache = useCalendarCache();
+  const [range, setRange] = useState(() => monthWindow(date, 3));
+  const [historyLoading, setHistoryLoading] = useState(false);
+  useEffect(() => { setRange(monthWindow(date, 3)); }, [date]);
   const [selectedDate, setSelectedDate] = useState<string>();
   const [editingDay, setEditingDay] = useState(false);
   const [savingDay, setSavingDay] = useState(false);
@@ -49,24 +54,18 @@ export function HabitHistory({
   const expired = useRef(onExpired);
   expired.current = onExpired;
   useEffect(() => {
-    const controller = new AbortController();
+    let active = true;
     setError("");
-    const range = monthWindow(date, 12);
-    habitRequest<CalendarResponse>(
-      `/habits/${habit.habitId}/calendar?${new URLSearchParams(range)}`,
-      { signal: controller.signal },
-    )
-      .then((result) => {
-        if (!controller.signal.aborted) setCalendar(result);
-      })
-      .catch((error) => {
-        if (controller.signal.aborted) return;
-        if (error.message.includes("session has expired") && expired.current)
-          expired.current();
+    setHistoryLoading(true);
+    cache.load(habit.habitId, `${date}:${revision}:${attempt}`, range)
+      .then(result => { if (active) setCalendar(result); })
+      .catch(error => {
+        if (!active) return;
+        if (error.message.includes("session has expired") && expired.current) expired.current();
         else setError(error.message);
-      });
-    return () => controller.abort();
-  }, [habit.habitId, date, revision, attempt]);
+      }).finally(() => { if (active) setHistoryLoading(false); });
+    return () => { active = false; };
+  }, [cache, habit.habitId, date, revision, attempt, range.from, range.to]);
 
   const days =
     calendar?.days.map((day) => ({
@@ -123,6 +122,9 @@ export function HabitHistory({
       selectedDate={selectedDate}
       compact
       initialMonths={3}
+      availableRange={monthWindow(date, 12)}
+      onRangeChange={setRange}
+      loading={historyLoading}
       historyLabel="Your recorded progress"
       label={`${habit.name} progress calendar`}
       unit={habit.unit}

src/components/design-system/CalendarHeatmap.tsx

@@ -10,6 +10,7 @@ import {
   calendarTimeline,
   MONTH_VIEWS,
   visibleCalendarDays,
+  monthWindow,
   type CalendarDay,
   type MonthView,
 } from "./calendar-model";
@@ -26,7 +27,13 @@ export function CalendarHeatmap({
   historyLabel,
   legend,
   selectedDayAction,
+  availableRange,
+  onRangeChange,
+  loading = false,
 }: {
+  availableRange?: { from: string; to: string };
+  onRangeChange?: (range: { from: string; to: string }) => void;
+  loading?: boolean;
   days: CalendarDay[];
   unit: string;
   label: string;
@@ -100,6 +107,7 @@ export function CalendarHeatmap({
     <div
       className={`ds-calendar${compact ? " ds-calendar--compact" : ""}`}
       data-months={months}
+      aria-busy={loading}
       style={{ "--calendar-weeks": timeline.weeks, "--calendar-color": color } as CSSProperties}
     >
       <div className="ds-calendar-range-toolbar">
@@ -130,7 +138,7 @@ export function CalendarHeatmap({
               type="button"
               aria-label={`${value} ${value === 1 ? "month" : "months"}`}
               aria-pressed={months === value}
-              onClick={() => setMonths(value)}
+              onClick={() => { setMonths(value); if (anchor) onRangeChange?.(monthWindow(anchor, value)); }}
             >
               {value}m
             </button>
@@ -160,7 +168,7 @@ export function CalendarHeatmap({
             const end = form.elements.namedItem("to") as HTMLInputElement;
             const isAvailable = (input: HTMLInputElement) =>
               input.validity.valid && input.value !== "" &&
-              input.value >= allDays[0]!.date && input.value <= allDays.at(-1)!.date;
+              input.value >= (availableRange?.from ?? allDays[0]!.date) && input.value <= (availableRange?.to ?? allDays.at(-1)!.date);
             if (!isAvailable(start) || !isAvailable(end)) {
               setRangeError("Choose both dates within the available history.");
               (!isAvailable(start) ? start : end).focus();
@@ -171,11 +179,12 @@ export function CalendarHeatmap({
               end.focus();
               return;
             }
-            if (!allDays.some((day) => day.date >= start.value && day.date <= end.value)) {
+            if (!availableRange && !allDays.some((day) => day.date >= start.value && day.date <= end.value)) {
               setRangeError("There are no calendar dates in this range.");
               return;
             }
             setCustomRange({ from: start.value, to: end.value });
+            onRangeChange?.({ from: start.value, to: end.value });
             setRangeError("");
           }}
         >
@@ -187,8 +196,8 @@ export function CalendarHeatmap({
                   name={name}
                   type="date"
                   required
-                  min={allDays[0]!.date}
-                  max={allDays.at(-1)!.date}
+                  min={availableRange?.from ?? allDays[0]!.date}
+                  max={availableRange?.to ?? allDays.at(-1)!.date}
                   defaultValue={customRange[name]}
                   aria-invalid={rangeError ? true : undefined}
                   aria-describedby={rangeError ? rangeErrorId : undefined}
@@ -201,6 +210,7 @@ export function CalendarHeatmap({
           {rangeError && <p id={rangeErrorId} className="ds-calendar-range-error" role="alert">{rangeError}</p>}
         </form>
       )}
+      {loading && <p role="status" className="ds-supporting-copy">Loading history…</p>}
       <div
         className="ds-calendar-viewport"
         role="group"

src/lib/dashboard.ts

@@ -1,7 +1,7 @@
 import type { HabitService } from "../habits/service";
 import type { Schedule } from "../habits/contracts";
 
-export type TodayHabit = ReturnType<HabitService["day"]>;
+export type TodayHabit = ReturnType<HabitService["day"]> & { calendarRevision?: number };
 export type TodayResponse = {
   date: string;
   timezone: string;

src/pages/Home.tsx

@@ -1,3 +1,4 @@
+import { CalendarCacheProvider } from "../components/CalendarCache";
 import { Archive, Plus, Settings2 } from "lucide-react";
 import { ArchivedHabits } from "../components/ArchivedHabits";
 import { AccountSettings } from "../components/AccountSettings";
@@ -63,7 +64,7 @@ export function Home() {
           </Card>
         </section>
       ) : user ? (
-        <Dashboard key={user.id} user={user} onExpired={retry} />
+        <CalendarCacheProvider key={`${user.id}:${user.timezone}`}><Dashboard user={user} onExpired={retry} /></CalendarCacheProvider>
       ) : (
         <Welcome onSignIn={signIn} />
       )}
@@ -163,7 +164,6 @@ function Dashboard({ user, onExpired }: { user: PublicUser; onExpired: () => voi
   const [today, setToday] = useState<TodayResponse | null>(null);
   const [error, setError] = useState("");
   const [revision, setRevision] = useState(0);
-  const [calendarRevision, setCalendarRevision] = useState(0);
   const [habitRevisions, setHabitRevisions] = useState<Record<string, number>>({});
   const [pendingHabits, setPendingHabits] = useState<Set<string>>(new Set());
   const progressSaves = useRef(new Set<string>());
@@ -206,7 +206,6 @@ function Dashboard({ user, onExpired }: { user: PublicUser; onExpired: () => voi
           setToday(data);
           setNeedsRefresh(false);
           setRevision((value) => value + 1);
-          setCalendarRevision((value) => value + 1);
         }
       })
       .catch((error) => {
@@ -457,7 +456,7 @@ function Dashboard({ user, onExpired }: { user: PublicUser; onExpired: () => voi
                     key={habit.habitId}
                     habit={habit}
                     date={today.date}
-                    revision={calendarRevision + (habitRevisions[habit.habitId] ?? 0)}
+                    revision={habit.calendarRevision ?? habitRevisions[habit.habitId] ?? 0}
                     disabled={busy || pendingHabits.has(habit.habitId) || loading || needsRefresh}
                     onHistorySaved={() => setAttempt(value => value + 1)}
                     onUpdate={update}