fix(medications): surface a multi-day-overdue first rolling dose

A rolling cadence with no intake logged anchors its first dose at
startsOn ?? createdAt. When that anchor falls on a prior calendar day
the dose is overdue by a day or more, but nextOccurrenceAfter floored
the search window to the start of the user's current day and dropped it
— so the dashboard showed no next-due and the reminder worker, which
shares this engine, emitted nothing. Clamp the floor to the first-dose
day in the no-intake branch so a multi-day-overdue start dose surfaces
as overdue. The post-intake re-anchor (lastIntakeAt + N) is unaffected.

src/lib/medications/scheduling/__tests__/recurrence.test.ts

@@ -392,6 +392,38 @@ describe("occurrencesBetween — rolling", () => {
     ).toBe("2026-06-10");
   });
 
+  it("nextOccurrenceAfter surfaces a multi-day-overdue first dose (startsOn days ago, no intake)", () => {
+    // v1.8.5 — a rolling course whose startsOn is several calendar days in
+    // the past with no intake logged must still surface the start dose as
+    // OVERDUE ("take now"). Flooring the search window only to the start of
+    // the user's current day dropped the dose out of existence, returning
+    // null — no next-due AND no reminder. The floor must reach back to the
+    // first-dose instant in the no-intake case.
+    const startsOn = d("2026-06-07T06:00:00Z"); // 3 days before NOW
+    const NOW = d("2026-06-10T12:00:00Z");
+    const schedule = makeSchedule({
+      rollingIntervalDays: 7,
+      timesOfDay: ["08:00"],
+    });
+    const ctx = makeCtx({
+      lastIntakeAt: null,
+      medication: { startsOn },
+    });
+    const next = nextOccurrenceAfter(schedule, NOW, ctx);
+    expect(next).not.toBeNull();
+    // The surfaced slot is the start dose (08:00 Berlin on the startsOn day),
+    // overdue by ~3 days relative to NOW.
+    expect(next!.at.getTime()).toBeLessThan(NOW.getTime());
+    expect(
+      new Intl.DateTimeFormat("en-CA", {
+        timeZone: "Europe/Berlin",
+        year: "numeric",
+        month: "2-digit",
+        day: "2-digit",
+      }).format(next!.at),
+    ).toBe("2026-06-07");
+  });
+
   it("nextOccurrenceAfter returns the future first dose AT startsOn (no intake) without adding N", () => {
     const NOW = d("2026-06-10T12:00:00Z");
     const startsOn = d("2026-06-12T00:00:00Z"); // 2 days out

src/lib/medications/scheduling/recurrence.ts

@@ -259,9 +259,21 @@ export function nextOccurrenceAfter(
   // of its due day instead of silently rolling it forward by N.
   if (schedule.rollingIntervalDays !== null) {
     const dayFloor = startOfDayInTz(after, ctx.timeZone);
-    const slots = expandRolling(schedule, ctx, dayFloor, limit);
+    // With no intake logged the first dose anchors at `startsOn ?? createdAt`.
+    // When that anchor is on a PRIOR calendar day the dose is overdue by ≥1
+    // day and must still surface ("take now"); flooring only to the start of
+    // the user's current day dropped it out of existence (null next-due AND
+    // no reminder). Reach the floor back to the first-dose instant in that
+    // case so a multi-day-overdue start dose is returned. After an intake the
+    // re-anchor (`lastIntakeAt + N`) is always in the future, so the dayFloor
+    // is the correct, tighter bound there.
+    const floor =
+      ctx.lastIntakeAt === null
+        ? new Date(Math.min(dayFloor.getTime(), firstRollingDoseDayFloor(ctx)))
+        : dayFloor;
+    const slots = expandRolling(schedule, ctx, floor, limit);
     for (const s of slots) {
-      if (s.at.getTime() < dayFloor.getTime()) continue;
+      if (s.at.getTime() < floor.getTime()) continue;
       if (cyclic && !isInCyclicOnWeek(s.at, schedule, ctx)) continue;
       return s;
     }
@@ -367,6 +379,19 @@ function expandOneShot(
  * historical intake events, not "expected slots" the schedule
  * predicts forward.
  */
+/**
+ * Start-of-day (in the user's timezone) of the no-intake first rolling dose
+ * anchor — `startsOn ?? createdAt`. Used by `nextOccurrenceAfter` to clamp the
+ * search floor so a multi-day-overdue first dose still surfaces. Mirrors the
+ * anchor `expandRolling` emits in the `lastIntakeAt === null` branch; flooring
+ * to the anchor's start-of-day keeps the time-of-day slot (e.g. 08:00) within
+ * the window rather than ahead of a raw-instant floor.
+ */
+function firstRollingDoseDayFloor(ctx: RecurrenceContext): number {
+  const anchor = ctx.medication.startsOn ?? ctx.medication.createdAt;
+  return startOfDayInTz(anchor, ctx.timeZone).getTime();
+}
+
 function expandRolling(
   schedule: CanonicalSchedule,
   ctx: RecurrenceContext,