fix(measurements): isolate per-type failures in the series batch

The batched daily-series endpoint ran every type through one Promise.all
with no per-task catch, so a single type's transient reject 500'd the whole
batch and blanked every preloaded chart in the dashboard row at once.

Wrap each per-type read so a failure degrades to an empty slice for that
type only; the failing chart self-fetches through its existing fallback.
A degraded_types counter rides the wide event.

src/app/api/measurements/series-batch/__tests__/route.test.ts

@@ -117,4 +117,24 @@ describe("GET /api/measurements/series-batch", () => {
     expect(res.status).toBe(200);
     expect(vi.mocked(readDailySeries)).toHaveBeenCalledTimes(1);
   });
+
+  it("isolates a single type's failure to an empty slice, others still return", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    const weightRows = [
+      { type: "WEIGHT", value: 80, measuredAt: FROM, count: 1 },
+    ];
+    vi.mocked(readDailySeries).mockImplementation(async ({ type }) => {
+      if (type === "WEIGHT") return weightRows as never;
+      throw new Error("transient db reject");
+    });
+
+    const res = await GET(
+      req(`types=WEIGHT,BLOOD_PRESSURE_SYS&from=${FROM}&to=${TO}`),
+    );
+    // One type rejecting must NOT 500 the whole batch.
+    expect(res.status).toBe(200);
+    const body = await res.json();
+    expect(body.data.series.WEIGHT).toEqual(weightRows);
+    expect(body.data.series.BLOOD_PRESSURE_SYS).toEqual([]);
+  });
 });

src/app/api/measurements/series-batch/route.ts

@@ -63,18 +63,27 @@ export const GET = apiHandler(async (request: NextRequest) => {
   // so the batched reader doesn't re-query it per type.
   const priorityJson = await loadUserSourcePriority(user.id);
 
+  // Per-type isolation: a single type's transient DB reject degrades to an
+  // empty slice for THAT type only, never a 500 that blanks every chart in
+  // the row. The failing chart self-fetches through its existing fallback.
   const limit = pLimit(SERIES_BATCH_CONCURRENCY);
+  let degradedTypes = 0;
   const entries = await Promise.all(
     uniqueTypes.map((type) =>
-      limit(async () => {
-        const rows = await readDailySeries({
-          userId: user.id,
-          type,
-          from,
-          to,
-          priorityJson,
-        });
-        return [type, rows] as const;
+      limit(async (): Promise<readonly [MeasurementType, DailySeriesRow[]]> => {
+        try {
+          const rows = await readDailySeries({
+            userId: user.id,
+            type,
+            from,
+            to,
+            priorityJson,
+          });
+          return [type, rows] as const;
+        } catch {
+          degradedTypes += 1;
+          return [type, []] as const;
+        }
       }),
     ),
   );
@@ -89,6 +98,7 @@ export const GET = apiHandler(async (request: NextRequest) => {
     meta: {
       type_count: uniqueTypes.length,
       total: entries.reduce((sum, [, rows]) => sum + rows.length, 0),
+      degraded_types: degradedTypes,
     },
   });