Keep the rolling anchor when a start only moved forward

An intake before startsOn stopped anchoring a rolling cadence, which
also moved the next dose of a single-course medication whose start had
merely been pushed forward a few days. The intake is now ignored only
when the dose it implies would fall before the course starts (a new
course after a gap); otherwise it anchors as before.

src/lib/analytics/compliance/cycle.ts

@@ -158,15 +158,18 @@ export function buildCurrentCycle(
     if (canonical.scheduleType === "PRN") continue;
     const n = canonical.rollingIntervalDays;
     if (n !== null && n > 0) {
-      // v1.40 (#1024) — an intake from a previous course does not anchor the
-      // current one; its first dose is due on its start day.
-      const intakeInCourse =
-        lastIntakeAt !== null &&
-        (ctx.startsOn === null ||
-          userDayKey(lastIntakeAt, ctx.timeZone) >= dayKeyOfDate(ctx.startsOn));
-      const anchor =
-        intakeInCourse && lastIntakeAt !== null
+      // v1.40 (#1024) — an intake whose next dose would fall before the
+      // course starts belongs to an earlier course and does not anchor this
+      // one (the recurrence engine's rule); otherwise it anchors as before.
+      const fromIntake =
+        lastIntakeAt !== null
           ? new Date(lastIntakeAt.getTime() + n * DAY_MS)
+          : null;
+      const anchor =
+        fromIntake !== null &&
+        (ctx.startsOn === null ||
+          userDayKey(fromIntake, ctx.timeZone) >= dayKeyOfDate(ctx.startsOn))
+          ? fromIntake
           : (ctx.startsOn ?? ctx.createdAt);
       if (ctx.endsOn && anchor.getTime() > ctx.endsOn.getTime()) continue;
       const graceMs = (canonical.reminderGraceMinutes ?? 60) * 60 * 1000;

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

@@ -242,6 +242,29 @@ describe("occurrencesBetween — RRULE MONTHLY / YEARLY", () => {
 // ────────────────────────────────────────────────────────────────────
 
 describe("occurrencesBetween — rolling", () => {
+  it("keeps anchoring on an intake when the start was only moved forward a little (v1.40)", () => {
+    // Weekly. Last dose Jun 8; the start was then moved to Jun 10. The next
+    // dose stays Jun 15 (last dose + 7), as it was before courses existed.
+    const NOW = d("2026-06-11T12:00:00Z");
+    const schedule = makeSchedule({
+      rollingIntervalDays: 7,
+      timesOfDay: ["08:00"],
+    });
+    const ctx = makeCtx({
+      lastIntakeAt: d("2026-06-08T06:00:00Z"),
+      medication: { startsOn: d("2026-06-10T00:00:00Z") },
+    });
+    const slots = occurrencesBetween(
+      schedule,
+      NOW,
+      new Date(NOW.getTime() + 14 * 24 * 60 * 60 * 1000),
+      ctx,
+    );
+    expect(slots.map((o) => o.at.toISOString())).toEqual([
+      "2026-06-15T06:00:00.000Z",
+    ]);
+  });
+
   it("does not let an intake from a previous course anchor a new one (v1.40, #1024)", () => {
     // The previous course's last dose was months ago; the new course starts
     // in two days. Its first dose is due on its start day, not on

src/lib/medications/scheduling/recurrence.ts

@@ -493,23 +493,28 @@ function rollingDoseAnchor(
   ctx: RecurrenceContext,
 ): Date {
   const intervalDays = schedule.rollingIntervalDays ?? 0;
-  // v1.40 (#1024) — an intake from before the course started (a previous
-  // course of the same medication) does not anchor this one: the new
-  // course's first dose is due on its start day, as for a course with no
-  // intake at all.
-  const intakeDay =
-    ctx.lastIntakeAt !== null
-      ? civilDayOfInstant(ctx.lastIntakeAt, ctx.timeZone)
-      : null;
-  const anchorsThisCourse =
-    intakeDay !== null &&
-    (ctx.medication.startsOn === null ||
-      intakeDay.getTime() >= civilDayOfDate(ctx.medication.startsOn).getTime());
   // N calendar days after the local day of the last intake, not N × 24 h:
   // a late-evening dose across a DST change would otherwise slide onto the
   // wrong day.
-  return anchorsThisCourse
-    ? addCivilDays(intakeDay, intervalDays)
+  const fromIntake =
+    ctx.lastIntakeAt !== null
+      ? addCivilDays(
+          civilDayOfInstant(ctx.lastIntakeAt, ctx.timeZone),
+          intervalDays,
+        )
+      : null;
+  // v1.40 (#1024) — an intake whose next dose would fall before the course
+  // starts belongs to an earlier course (a new course after a gap): it does
+  // not anchor this one, whose first dose is due on its start day. An intake
+  // whose next dose falls on or after the start (a start moved forward by a
+  // few days) anchors exactly as before.
+  const startDay =
+    ctx.medication.startsOn !== null
+      ? civilDayOfDate(ctx.medication.startsOn)
+      : null;
+  return fromIntake !== null &&
+    (startDay === null || fromIntake.getTime() >= startDay.getTime())
+    ? fromIntake
     : anchorCivilDay(ctx);
 }