fix(due,store,ui): month grid steps by calendar day so dst cannot repeat one

src/lib/due.ts

@@ -29,10 +29,14 @@ export function shiftDays(key: string, days: number): string {
   return localKey(date);
 }
 
-/** Milliseconds until the next local midnight, with a little slack past it. */
-export function untilMidnight(now = new Date()): number {
-  const next = new Date(now.getFullYear(), now.getMonth(), now.getDate() + 1);
-  return Math.max(1000, next.getTime() - now.getTime() + 500);
+export function monthGrid(month: Date): Date[] {
+  const year = month.getFullYear();
+  const index = month.getMonth();
+  const offset = (new Date(year, index, 1).getDay() + 6) % 7;
+  return Array.from(
+    { length: 42 },
+    (_, cell) => new Date(year, index, 1 - offset + cell),
+  );
 }
 
 export function daysFromToday(key: string, from = today()): number {

src/ui/day-grid.svelte

@@ -5,7 +5,7 @@
 <script lang="ts">
   import ChevronLeft from "@lucide/svelte/icons/chevron-left";
   import ChevronRight from "@lucide/svelte/icons/chevron-right";
-  import { fromKey, localKey } from "../lib/due";
+  import { fromKey, localKey, monthGrid } from "../lib/due";
   import { WEEKDAYS } from "../lib/vocab";
   import { cn } from "../lib/utils";
 
@@ -20,7 +20,6 @@
 
   let { anchor, tone, onpick, onhover, today }: Props = $props();
 
-  const DAY = 86_400_000;
   const monthName = new Intl.DateTimeFormat("en-US", { month: "long" });
   const todayKey = $derived(today ?? localKey(new Date()));
 
@@ -32,20 +31,13 @@
     return new Date(base.getFullYear(), base.getMonth(), 1);
   });
 
-  const days = $derived.by(() => {
-    const offset = (month.getDay() + 6) % 7;
-    const start = new Date(month.getTime() - offset * DAY);
-    start.setHours(0, 0, 0, 0);
-    return Array.from({ length: 42 }, (_, index) => {
-      const date = new Date(start.getTime() + index * DAY);
-      date.setHours(0, 0, 0, 0);
-      return {
+  const days = $derived(
+    monthGrid(month).map((date) => ({
       date,
       inMonth: date.getMonth() === month.getMonth(),
       key: localKey(date),
-      };
-    });
-  });
+    })),
+  );
 
   function shiftMonth(delta: number) {
     picked = new Date(month.getFullYear(), month.getMonth() + delta, 1);

src/vault/store.svelte.ts

@@ -4,7 +4,7 @@ import { isArchivePath, toBoardPath } from "../model/archive";
 import { parseBoard, sphereOf } from "../model/board";
 import { anchorDate, isOpen, STATUS_ORDER } from "../model/types";
 import type { Board, Status, Task } from "../model/types";
-import { daysFromToday, fromKey, localKey, shiftDays, untilMidnight } from "../lib/due";
+import { daysFromToday, fromKey, localKey, monthGrid, shiftDays } from "../lib/due";
 import { laneKey, parseLaneKey } from "../lib/keys";
 import type {
   BeaverCalendarSettings,
@@ -13,7 +13,6 @@ import type {
   ViewMode,
 } from "../settings";
 
-const DAY = 86_400_000;
 
 export interface Group {
   key: string;
@@ -197,37 +196,35 @@ export class BoardStore {
     this.settings = settings;
   }
 
-  /** Re-reads the wall clock; a no-op while the day has not turned. */
+  /**
+   * Re-reads the wall clock; a no-op while the day has not turned. A cursor
+   * left on the old today, and a month showing it, follow the day over.
+   */
   tick(): void {
     const now = localKey(new Date());
-    if (now !== this.today) this.today = now;
+    const was = this.today;
+    if (now === was) return;
+    this.today = now;
+    if (this.cursorDay === was && this.cursorTask === null) this.cursorDay = now;
+    if (this.monthKey.slice(0, 7) === was.slice(0, 7)) this.monthKey = now;
   }
 
   /**
-   * Keeps `today` honest for as long as the view lives: a timer for the
-   * midnight crossing, and a re-read when the window wakes up, since a
-   * sleeping laptop fires no timers.
+   * Keeps `today` honest for as long as the view lives. The clock is polled
+   * rather than timed to midnight: Chromium's timers stop while a Mac sleeps,
+   * so a midnight timeout fires hours late, and a window that stayed focused
+   * through the sleep sends no focus event on waking. Waking still re-reads
+   * at once where the events do come.
    */
   watchClock(): () => void {
-    let timer = 0;
-    const arm = (): void => {
-      window.clearTimeout(timer);
-      timer = window.setTimeout(() => {
-        this.tick();
-        arm();
-      }, untilMidnight());
-    };
-    const wake = (): void => {
-      this.tick();
-      arm();
-    };
-    arm();
-    window.addEventListener("focus", wake);
-    document.addEventListener("visibilitychange", wake);
+    const tick = (): void => this.tick();
+    const timer = window.setInterval(tick, 30_000);
+    window.addEventListener("focus", tick);
+    document.addEventListener("visibilitychange", tick);
     return () => {
-      window.clearTimeout(timer);
-      window.removeEventListener("focus", wake);
-      document.removeEventListener("visibilitychange", wake);
+      window.clearInterval(timer);
+      window.removeEventListener("focus", tick);
+      document.removeEventListener("visibilitychange", tick);
     };
   }
 
@@ -451,13 +448,9 @@ export class BoardStore {
   monthDays = $derived.by<DaySlot[]>(() => {
     const anchor = fromKey(this.monthKey);
     const first = new Date(anchor.getFullYear(), anchor.getMonth(), 1);
-    const offset = (first.getDay() + 6) % 7;
-    const start = new Date(first.getTime() - offset * DAY);
     const todayKey = this.today;
     const byDay = this.byDay;
-    return Array.from({ length: 42 }, (_, index) => {
-      const date = new Date(start.getTime() + index * DAY);
-      date.setHours(0, 0, 0, 0);
+    return monthGrid(first).map((date) => {
       const key = localKey(date);
       return {
         date,

tests/due.test.ts

@@ -1,10 +1,11 @@
-import { describe, expect, it } from "vitest";
+import { afterAll, beforeAll, describe, expect, it } from "vitest";
 import {
   daysFromToday,
   dueLabel,
   dueTone,
+  localKey,
+  monthGrid,
   nextFriday,
-  untilMidnight,
 } from "../src/lib/due";
 
 describe("due helpers read the day they are given", () => {
@@ -26,12 +27,31 @@ describe("due helpers read the day they are given", () => {
     expect(nextFriday("2026-08-23")).toBe("2026-08-28");
     expect(nextFriday("2026-08-28")).toBe("2026-09-04");
   });
+});
 
-  it("arms the midnight timer for the coming midnight", () => {
-    const late = new Date(2026, 7, 23, 23, 59, 0);
-    expect(untilMidnight(late)).toBeGreaterThan(60_000);
-    expect(untilMidnight(late)).toBeLessThan(62_000);
-    const early = new Date(2026, 7, 23, 0, 0, 1);
-    expect(untilMidnight(early)).toBeGreaterThan(23 * 3_600_000);
+describe("monthGrid steps by calendar day", () => {
+  const zone = process.env.TZ;
+  beforeAll(() => {
+    process.env.TZ = "Europe/Berlin";
+  });
+  afterAll(() => {
+    process.env.TZ = zone;
+  });
+
+  it("keeps every day once across the autumn clock change", () => {
+    const keys = monthGrid(new Date(2026, 9, 1)).map(localKey);
+    expect(keys).toHaveLength(42);
+    expect(new Set(keys).size).toBe(42);
+    expect(keys[0]).toBe("2026-09-28");
+    expect(keys[27]).toBe("2026-10-25");
+    expect(keys[28]).toBe("2026-10-26");
+    expect(keys[41]).toBe("2026-11-08");
+  });
+
+  it("keeps every day once across the spring clock change", () => {
+    const keys = monthGrid(new Date(2027, 2, 1)).map(localKey);
+    expect(new Set(keys).size).toBe(42);
+    expect(keys).toContain("2027-03-28");
+    expect(keys).toContain("2027-03-29");
   });
 });