fix(measurements): bound the per-night sleep list to a year ending at to

The sleep list capped its read to the last year only when no `from`
was sent. An explicit early `from` walked every per-stage row back to
that date, on a multi-source account several rows per night for years.

The read window is now at most a year ending at `to` (or now). `from`
narrows it but never widens it, older nights are reached by moving
`to` back, and `meta.windowFrom` names the instant a cut window
started, so a client can tell a cut from an empty history.

src/app/api/measurements/route.ts

@@ -543,9 +543,18 @@ async function sleepListResponse(
     loadUserSourcePriority(user.id),
   ]);
 
-  // Bound the read window: honour an explicit from/to, otherwise cap to
-  // the last year so the per-stage scan stays small.
-  const since = from ?? new Date(Date.now() - SLEEP_LIST_MAX_DAYS * 86_400_000);
+  // Bound the read window to a year ending at `to` (or now). An explicit
+  // `from` narrows it but never widens it: an early `from` used to walk every
+  // per-stage row back to that date, which on a multi-year, multi-source
+  // account is the unbounded read this cap exists to stop. Older nights are
+  // reached by moving `to` back, and `meta.windowFrom` says where a cut
+  // window started so a client can tell a cut from an empty history.
+  const windowEnd = to ?? new Date();
+  const floor = new Date(
+    windowEnd.getTime() - SLEEP_LIST_MAX_DAYS * 86_400_000,
+  );
+  const since = from && from > floor ? from : floor;
+  const windowCut = from !== undefined && from < floor;
   const rows = await prisma.measurement.findMany({
     where: {
       userId: user.id,
@@ -690,7 +699,13 @@ async function sleepListResponse(
   });
   return apiSuccess({
     measurements,
-    meta: { total: totalNights, limit, offset, groupBy: "night" },
+    meta: {
+      total: totalNights,
+      limit,
+      offset,
+      groupBy: "night",
+      ...(windowCut ? { windowFrom: since.toISOString() } : {}),
+    },
   });
 }
 

src/lib/openapi/routes/measurements.ts

@@ -389,6 +389,12 @@ const listMeasurementsMeta = z
       .describe(
         "Rows discarded by the cross-source canonical picker on the day-collapse mode.",
       ),
+    windowFrom: z.iso
+      .datetime({ offset: true })
+      .optional()
+      .describe(
+        "Set on the per-night SLEEP_DURATION mode when the requested window was longer than 365 days: the instant the read started from. The window is a year ending at `to` (or now); page further back by moving `to`.",
+      ),
   })
   .meta({ id: "ListMeasurementsMeta" });