Feature 19 follow-up: calendar week starts on Sunday (#230)

Co-authored-by: dev_agent <17+dev_agent@code.cubecraftcreations.com>
Co-committed-by: dev_agent <17+dev_agent@code.cubecraftcreations.com>

admin/src/schedule/ScheduleTab.test.tsx

@@ -131,10 +131,20 @@ describe("ScheduleTab", () => {
     expect(today.className).toContain("schedule-day--today");
     expect(today.dataset.state).toBe("home");
     expect(today.getAttribute("aria-label")).toBe("Sep 23 (today): Home");
-    // September 2026 starts on a Tuesday: one leading pad after the initials.
+    // Sunday-first header; September 2026 starts on a Tuesday: two leading pads.
     const grid = screen.getByRole("group", { name: "Month grid" });
+    expect(Array.from(grid.children, (c) => c.textContent).slice(0, 7)).toEqual([
+      "S",
+      "M",
+      "T",
+      "W",
+      "T",
+      "F",
+      "S",
+    ]);
     expect(grid.children[7].tagName).toBe("SPAN");
-    expect(grid.children[8].getAttribute("data-date")).toBe("2026-09-01");
+    expect(grid.children[8].tagName).toBe("SPAN");
+    expect(grid.children[9].getAttribute("data-date")).toBe("2026-09-01");
 
     const legend = screen.getByRole("list", { name: "Legend" });
     expect(within(legend).getAllByRole("listitem").map((li) => li.textContent)).toEqual([

admin/src/schedule/ScheduleTab.tsx

@@ -46,7 +46,8 @@ export const SCROLL_BOTTOM_PADDING = "92px";
 
 export const DEFAULT_CYCLE_LENGTH_WEEKS = 2;
 const CYCLE_LENGTH_CHOICES = [1, 2, 3, 4];
-const WEEKDAY_INITIALS = ["M", "T", "W", "T", "F", "S", "S"];
+/** Sunday-first header; `weekdayOf` stays Monday=0. */
+const WEEKDAY_INITIALS = ["S", "M", "T", "W", "T", "F", "S"];
 
 export const STATE_LABELS: Record<DayState, string> = {
   home: "Home",
@@ -130,7 +131,7 @@ interface MonthGridProps {
 
 function MonthGrid({ month, today, schedule, effective, overrides, onMonth, onToggle }: MonthGridProps) {
   const dates = monthDates(month);
-  const leading = weekdayOf(month);
+  const leading = (weekdayOf(month) + 1) % 7;
   return (
     <>
       <div className="schedule-month-head">

admin/src/schedule/cycle.test.ts

@@ -58,6 +58,24 @@ describe("calendar helpers", () => {
     expect(weekdayOf("2026-09-06")).toBe(6);
   });
 
+  it("weekdayOf keeps the stored Monday=0 .. Sunday=6 numbering (display order is separate)", () => {
+    // A full known week plus dates across month and year ends.
+    expect(
+      [
+        "2026-09-07",
+        "2026-09-08",
+        "2026-09-09",
+        "2026-09-10",
+        "2026-09-11",
+        "2026-09-12",
+        "2026-09-13",
+      ].map(weekdayOf),
+    ).toEqual([0, 1, 2, 3, 4, 5, 6]);
+    expect(weekdayOf("2026-11-01")).toBe(6); // Sunday
+    expect(weekdayOf("2027-01-01")).toBe(4); // Friday
+    expect(weekdayOf("2024-02-29")).toBe(3); // Thursday
+  });
+
   it("monthStart shifts across year ends", () => {
     expect(monthStart("2026-12-15", 1)).toBe("2027-01-01");
     expect(monthStart("2026-01-31", -1)).toBe("2025-12-01");