fix(health-score): leave today's partial step total out of the activity pillar

The activity pillar averaged the 28 days ending today, so any score computed
during the day counted a step total that was still growing and pulled the
average down. The window is now the 28 completed local days ending
yesterday, cut on day keys.

src/lib/analytics/score/__tests__/pillars.test.ts

@@ -25,6 +25,16 @@ function days(count: number, value: number) {
   }));
 }
 
+/** `count` completed days ending yesterday (activity leaves today out). */
+function completedDays(count: number, value: number) {
+  return Array.from({ length: count }, (_, index) => ({
+    day: new Date(NOW.getTime() - (index + 1) * 86_400_000)
+      .toISOString()
+      .slice(0, 10),
+    value,
+  }));
+}
+
 describe("reference-score pillars", () => {
   it("requires twelve fresh paired blood-pressure readings", () => {
     const below = computeBloodPressurePillar({
@@ -174,7 +184,7 @@ describe("reference-score pillars", () => {
         ...live,
         asOf: NOW,
         ageYears: 40,
-        days: days(20, 10_000),
+        days: completedDays(20, 10_000),
         sources: ["APPLE_HEALTH"],
       }).status,
     ).toBe("insufficient");
@@ -183,14 +193,14 @@ describe("reference-score pillars", () => {
       ...live,
       asOf: NOW,
       ageYears: 40,
-      days: days(21, 12_000),
+      days: completedDays(21, 12_000),
       sources: ["APPLE_HEALTH"],
     });
     const older = computeActivityPillar({
       ...live,
       asOf: NOW,
       ageYears: 68,
-      days: days(21, 8_000),
+      days: completedDays(21, 8_000),
       sources: ["APPLE_HEALTH"],
     });
     expect(younger.status).toBe("ok");
@@ -209,7 +219,7 @@ describe("reference-score pillars", () => {
       asOf: NOW,
       timezone: "Europe/Berlin",
       ageYears: 40,
-      days: days(21, 8_500),
+      days: completedDays(21, 8_500),
       sources: ["APPLE_HEALTH"],
     };
     const liveResult = computeActivityPillar({ ...input, source: "live" });
@@ -224,7 +234,7 @@ describe("reference-score pillars", () => {
   });
 
   it("scores exactly 28 activity calendar keys", () => {
-    const points = days(29, 10_000);
+    const points = completedDays(29, 10_000);
     points[28] = { ...points[28], value: 0 };
     const result = computeActivityPillar({
       ...live,
@@ -237,6 +247,64 @@ describe("reference-score pillars", () => {
     if (result.status === "ok") expect(result.value.score).toBe(100);
   });
 
+  it("leaves today's partial step total out of the window", () => {
+    const withToday = [
+      { day: "2026-07-28", value: 400 },
+      ...completedDays(21, 10_000),
+    ];
+    const result = computeActivityPillar({
+      ...live,
+      asOf: NOW,
+      ageYears: 40,
+      days: withToday,
+      sources: ["APPLE_HEALTH"],
+    });
+    expect(result.status).toBe("ok");
+    if (result.status === "ok") expect(result.value.score).toBe(100);
+
+    // Twenty completed days plus today are not enough days.
+    expect(
+      computeActivityPillar({
+        ...live,
+        asOf: NOW,
+        ageYears: 40,
+        days: [{ day: "2026-07-28", value: 400 }, ...completedDays(20, 10_000)],
+        sources: ["APPLE_HEALTH"],
+      }).status,
+    ).toBe("insufficient");
+  });
+
+  it.each([
+    ["America/New_York", "2026-03-09T03:30:00.000Z", "2026-03-08"],
+    ["Pacific/Auckland", "2026-04-05T11:00:00.000Z", "2026-04-05"],
+    ["Pacific/Tongatapu", "2026-07-28T11:30:00.000Z", "2026-07-29"],
+    ["America/Santiago", "2026-09-06T04:30:00.000Z", "2026-09-06"],
+    ["Europe/Berlin", "2026-10-25T23:30:00.000Z", "2026-10-26"],
+  ])("cuts the window on local days in %s", (timezone, iso, today) => {
+    const asOf = new Date(iso);
+    const [y, m, d] = today.split("-").map(Number);
+    const key = (back: number) =>
+      new Date(Date.UTC(y, m - 1, d - back)).toISOString().slice(0, 10);
+    const window = Array.from({ length: 28 }, (_, i) => ({
+      day: key(i + 1),
+      value: 10_000,
+    }));
+    const result = computeActivityPillar({
+      source: "live",
+      readFailed: false,
+      timezone,
+      asOf,
+      ageYears: 40,
+      days: [{ day: today, value: 0 }, { day: key(29), value: 0 }, ...window],
+      sources: ["APPLE_HEALTH"],
+    });
+    expect(result.status).toBe("ok");
+    if (result.status === "ok") {
+      expect(result.value.score).toBe(100);
+      expect(result.coverage.historyDays).toBe(28);
+    }
+  });
+
   it("requires fourteen sleep nights, never penalises long sleep, and adds regularity at 21 nights", () => {
     const below = computeSleepPillar({
       ...live,

src/lib/analytics/score/activity.ts

@@ -1,5 +1,5 @@
 import type { Derived } from "@/lib/insights/derived/types";
-import { userDayKey } from "@/lib/tz/format";
+import { shiftDateKey, userDayKey } from "@/lib/tz/format";
 
 import type { ActivityPillarInput, PillarValue } from "./types";
 import {
@@ -18,6 +18,23 @@ export const OLDER_ADULT_AGE = 60;
 export const YOUNGER_STEP_PLATEAU = 10_000;
 export const OLDER_STEP_PLATEAU = 8_000;
 
+/**
+ * The activity window: the `ACTIVITY_WINDOW_DAYS` completed local days that
+ * end yesterday, as inclusive `YYYY-MM-DD` keys. Today is left out because
+ * its step total is still growing: counting it pulled every score computed
+ * during the day down by a partial day.
+ */
+export function activityWindowKeys(
+  asOf: Date,
+  timezone: string,
+): { startDay: string; endDay: string } {
+  const today = userDayKey(asOf, timezone);
+  return {
+    startDay: shiftDateKey(today, -ACTIVITY_WINDOW_DAYS),
+    endDay: shiftDateKey(today, -1),
+  };
+}
+
 export function computeActivityPillar(
   input: ActivityPillarInput,
 ): Derived<PillarValue> {
@@ -29,13 +46,9 @@ export function computeActivityPillar(
     });
   }
 
-  const asOfDay = userDayKey(input.asOf, input.timezone);
-  const sinceDay = userDayKey(
-    new Date(input.asOf.getTime() - (ACTIVITY_WINDOW_DAYS - 1) * 86_400_000),
-    input.timezone,
-  );
+  const { startDay, endDay } = activityWindowKeys(input.asOf, input.timezone);
   const points = input.days.filter(
-    (point) => point.day <= asOfDay && point.day >= sinceDay,
+    (point) => point.day <= endDay && point.day >= startDay,
   );
   if (points.length < ACTIVITY_MIN_DAYS) {
     return insufficientPillar({

src/lib/analytics/score/reader.ts

@@ -23,7 +23,7 @@ import { getAgeFromDateOfBirth } from "@/lib/analytics/pulse-targets";
 import { healthScoreNoticeItemKey } from "@/lib/daily/priority-item-key";
 import { annotate, getEvent } from "@/lib/logging/context";
 
-import { ACTIVITY_WINDOW_DAYS } from "./activity";
+import { ACTIVITY_WINDOW_DAYS, activityWindowKeys } from "./activity";
 import { SLEEP_WINDOW_DAYS } from "./sleep";
 import { attachScoreDelta } from "./composite";
 import {
@@ -239,9 +239,8 @@ export async function readActivityDays(args: {
       canonical
         .filter((row) => {
           const day = userDayKey(row.measuredAt, args.timezone);
-          const endDay = userDayKey(args.asOf, args.timezone);
-          const startDay = userDayKey(
-            new Date(args.asOf.getTime() - (ACTIVITY_WINDOW_DAYS - 1) * DAY_MS),
+          const { startDay, endDay } = activityWindowKeys(
+            args.asOf,
             args.timezone,
           );
           return day >= startDay && day <= endDay;
@@ -461,10 +460,7 @@ function scoreInputsFor(args: {
   const { asOf, input } = args;
   const ageYears = getAgeFromDateOfBirth(input.profile.dateOfBirth);
   const asOfDay = userDayKey(asOf, input.profile.timezone);
-  const activitySinceDay = userDayKey(
-    new Date(asOf.getTime() - (ACTIVITY_WINDOW_DAYS - 1) * DAY_MS),
-    input.profile.timezone,
-  );
+  const activityWindow = activityWindowKeys(asOf, input.profile.timezone);
   const sleepSinceDay = userDayKey(
     new Date(asOf.getTime() - (SLEEP_WINDOW_DAYS - 1) * DAY_MS),
     input.profile.timezone,
@@ -548,7 +544,11 @@ function scoreInputsFor(args: {
       days: args.activity.value.days,
       sources: uniqueSources(
         args.activity.value.sourceDays
-          .filter((row) => row.day >= activitySinceDay && row.day <= asOfDay)
+          .filter(
+            (row) =>
+              row.day >= activityWindow.startDay &&
+              row.day <= activityWindow.endDay,
+          )
           .map((row) => row.source),
       ),
     },
@@ -629,7 +629,7 @@ export async function computeUserHealthScore(
   const db = input.prisma ?? prisma;
   const since = new Date(input.now.getTime() - SCORE_READ_DAYS * DAY_MS);
   const activitySince = new Date(
-    input.now.getTime() - (28 + HISTORY_OFFSET_DAYS) * DAY_MS,
+    input.now.getTime() - (ACTIVITY_WINDOW_DAYS + HISTORY_OFFSET_DAYS) * DAY_MS,
   );
   const [
     glucose,