fix(cycle): read the insights crosstab as per-source day aggregates

GET /api/cycle/insights read a year of raw readings for its outcome
channels, glucose and heart-rate variability included. On a sensor
account that is over 100 000 objects per request.

The crosstab uses each local day's sum and count after picking one
source and device per day, so the route now reads readSourceDayAggregates
like the coach's cycle snapshot does, and each row carries its reading
count into metricDayMap.

The integration test runs the route over the fold and over every raw
reading handed in as a one-reading group, and compares the answers.

src/app/api/cycle/insights/__tests__/route-locale.test.ts

@@ -37,6 +37,9 @@ vi.mock("@/lib/cycle/phase-crosstab", async (importOriginal) => ({
     discoverPhaseCorrelations(args),
 }));
 
+vi.mock("@/lib/measurements/day-aggregates", () => ({
+  readSourceDayAggregates: vi.fn().mockResolvedValue([]),
+}));
 vi.mock("@/lib/db", () => ({
   prisma: {
     auditLog: { create: vi.fn() },

src/app/api/cycle/insights/route.ts

@@ -43,6 +43,7 @@ import {
   type SymptomDay,
 } from "@/lib/cycle/symptom-phase";
 import { addDays } from "@/lib/cycle/day-math";
+import { readSourceDayAggregates } from "@/lib/measurements/day-aggregates";
 import { moodDateKey } from "@/lib/mood/date-key";
 import { DEFAULT_TIMEZONE } from "@/lib/tz/format";
 
@@ -130,27 +131,19 @@ export const GET = apiHandler(async () => {
       orderBy: { measuredAt: "asc" },
       select: { measuredAt: true, value: true },
     }),
-    // The outcome metrics the phase contrast compares — soft-delete-scoped,
-    // canonical-source deduped per day inside `metricDayMap`. Skipped whole
-    // for a caller outside `measurements`.
+    // The outcome metrics the phase contrast compares, soft-delete-scoped.
+    // A year of steps, heart-rate variability and sensor glucose is far too
+    // many readings to hold as objects (#1023), and the crosstab uses only
+    // each day's sum and count after picking one source and device per day.
+    // So the fold runs in SQL, one row per type, local day, source and
+    // device, the read the coach's cycle snapshot already makes. Skipped
+    // whole for a caller outside `measurements`.
     seesMeasurements
-      ? prisma.measurement.findMany({
-          where: {
-            userId: user.id,
-            deletedAt: null,
-            type: { in: PHASE_CROSSTAB_METRIC_TYPES },
-            measuredAt: {
-              gte: new Date(Date.parse(`${from}T00:00:00Z`)),
-            },
-          },
-          orderBy: { measuredAt: "asc" },
-          select: {
-            type: true,
-            value: true,
-            measuredAt: true,
-            source: true,
-            deviceType: true,
-          },
+      ? readSourceDayAggregates({
+          userId: user.id,
+          types: PHASE_CROSSTAB_METRIC_TYPES,
+          since: new Date(Date.parse(`${from}T00:00:00Z`)),
+          timeZone: tz,
         })
       : [],
     prisma.user.findUnique({
@@ -200,10 +193,13 @@ export const GET = apiHandler(async () => {
     today,
   );
 
+  // Each row stands for its day's readings: `value` is their sum and
+  // `count` their number, so `metricDayMap` gets the raw readings' day mean.
   const measurements: CrossMetricMeasurement[] = measurementRows.map((m) => ({
     type: m.type,
-    value: m.value,
-    measuredAt: m.measuredAt,
+    value: m.sum,
+    count: m.n,
+    measuredAt: m.firstAt,
     source: m.source,
     deviceType: m.deviceType,
   }));