fix(measurements): keep a folded hour out of a blood-pressure reading

The reading delete found the cuff's pulse by owner, source and identical
instant. The dense fold anchors an hour of heart rate at the local HH:30
under the samples' source, so a reading taken at half past took that hour
with it. Aggregate (stats:) rows are never part of a reading now, for the
delete and for the restore.

src/lib/measurements/blood-pressure-reading.ts

@@ -14,6 +14,14 @@
  * Deleting a systolic or a diastolic takes the whole reading with it.
  * Deleting a pulse takes only the pulse: a pulse is also a value of its own,
  * and removing one is no reason to remove a blood pressure.
+ *
+ * An aggregate row is never part of a reading. The dense fold stores an
+ * hour of heart rate as one `stats:` row at the local HH:30 of that hour
+ * (`canonicalHourlyTimestamp`), under the same source as the samples it
+ * folded, and the client's hourly heart-rate bucket is a `stats:` row as
+ * well. A cuff reading taken at half past, from the same source, shares its
+ * instant with that row; it is still an hour of somebody's heart rate, not
+ * the cuff's pulse, and a delete must not take it.
  */
 import type { MeasurementType, Prisma } from "@/generated/prisma/client";
 
@@ -30,6 +38,9 @@ const BP_READING_TYPES: MeasurementType[] = [
   "PULSE",
 ];
 
+/** The externalId prefix every aggregate (folded or bucketed) row carries. */
+const AGGREGATE_EXTERNAL_ID_PREFIX = "stats:";
+
 export interface ReadingAnchor {
   id: string;
   type: MeasurementType | string;
@@ -70,6 +81,20 @@ export async function bloodPressureSiblings(
       userId,
       id: { notIn: rows.map((r) => r.id) },
       type: { in: BP_READING_TYPES },
+      // Spelled with the NULL arm: a bare `NOT startsWith` is NULL, not
+      // true, for the NULL externalId of a manual row and would drop it.
+      AND: [
+        {
+          OR: [
+            { externalId: null },
+            {
+              NOT: {
+                externalId: { startsWith: AGGREGATE_EXTERNAL_ID_PREFIX },
+              },
+            },
+          ],
+        },
+      ],
       OR: anchors.map((a) => ({
         source: a.source as Prisma.MeasurementWhereInput["source"],
         measuredAt: a.measuredAt,