refactor(analytics): hoist cumulative metric-key lookup out of nested ternary

Pulls the v1.4.36 W4c MeasurementType -> SourcePriorityMetricKey
chain out of the dashboard per-type loop into a typed switch helper.
Same call sites, same null fallback for the unmapped TIME_IN_DAYLIGHT
branch.

src/app/api/analytics/route.ts

@@ -29,6 +29,7 @@ import type {
 } from "@/generated/prisma/client";
 import { measurementTypeEnum } from "@/lib/validations/measurement";
 import { pickCanonicalSourceRows } from "@/lib/analytics/source-priority";
+import type { SourcePriorityMetricKey } from "@/lib/validations/source-priority";
 import { ensureUserRollupsFresh } from "@/lib/measurements/rollups";
 import {
   isCumulativeDaySumType,
@@ -37,6 +38,29 @@ import {
 
 export const dynamic = "force-dynamic";
 
+/**
+ * v1.4.36 W4c — cumulative MeasurementType → SourcePriorityMetricKey
+ * for `pickCanonicalSourceRows`. Returns `null` for types without a
+ * dedicated priority ladder (e.g. TIME_IN_DAYLIGHT), which fall
+ * through the picker's "no ladder" pass-through branch.
+ */
+function cumulativeMetricKey(
+  type: MeasurementType,
+): SourcePriorityMetricKey | null {
+  switch (type) {
+    case "ACTIVITY_STEPS":
+      return "steps";
+    case "ACTIVE_ENERGY_BURNED":
+      return "activeEnergy";
+    case "WALKING_RUNNING_DISTANCE":
+      return "walkingRunningDistance";
+    case "FLIGHTS_CLIMBED":
+      return "flightsClimbed";
+    default:
+      return null;
+  }
+}
+
 /**
  * v1.4.33 C1 — pull `?slice=…` from either a NextRequest (the
  * route's production wrapper) or a plain `Request` (the integration
@@ -234,16 +258,7 @@ async function buildAnalyticsResponse(user: AuthedUser) {
           // through `pickCanonicalSourceRows`'s "no ladder"
           // pass-through branch — we ALWAYS bucket-and-sum it
           // regardless of source.
-          const metricKey =
-            type === "ACTIVITY_STEPS"
-              ? ("steps" as const)
-              : type === "ACTIVE_ENERGY_BURNED"
-                ? ("activeEnergy" as const)
-                : type === "WALKING_RUNNING_DISTANCE"
-                  ? ("walkingRunningDistance" as const)
-                  : type === "FLIGHTS_CLIMBED"
-                    ? ("flightsClimbed" as const)
-                    : null;
+          const metricKey = cumulativeMetricKey(type);
           const canonicalRows = metricKey
             ? pickCanonicalSourceRows(
                 measurements,