fix(sources): stop listing a source whose readings were all deleted

The in-use probe matched tombstoned readings, so a source stayed marked
on the priority ladder after every reading from it was deleted. Both
the read and the save response of the source-priority route go through
this one probe.

src/lib/integrations/__tests__/sources-in-use.test.ts

@@ -38,6 +38,21 @@ describe("getSourcesInUse", () => {
     expect(await getSourcesInUse("u1")).toEqual(["MANUAL"]);
   });
 
+  it("does not count a source whose readings were all deleted", async () => {
+    // The probe answers like the database: a MANUAL row exists, but it is a
+    // tombstone, so only a probe that admits deleted rows finds it.
+    vi.mocked(prisma.measurement.findFirst).mockImplementation(((args: {
+      where: { source: string; deletedAt?: null };
+    }) =>
+      Promise.resolve(
+        args.where.source === "MANUAL" && !("deletedAt" in args.where)
+          ? { id: "m-deleted" }
+          : null,
+      )) as never);
+
+    expect(await getSourcesInUse("u1")).toEqual([]);
+  });
+
   it("lists a connected integration that has not delivered yet", async () => {
     vi.mocked(prisma.measurement.findFirst).mockResolvedValue(null);
     vi.mocked(prisma.withingsConnection.findUnique).mockResolvedValue({

src/lib/integrations/sources-in-use.ts

@@ -17,7 +17,8 @@ export const RANKABLE_SOURCES: readonly MeasurementSource[] = Array.from(
  * one measurement from, or an integration it has connected that has not
  * delivered yet.
  *
- * The Settings ladder lists only these. Ranking a source the person has never
+ * Deleted (tombstoned) readings do not count. The Settings ladder lists only
+ * these. Ranking a source the person has never
  * used decides nothing, and ten of them per metric buried the two that do.
  * The ladders themselves stay whole: hidden sources keep their slot, so a
  * source that starts delivering later lands where the ladder already put it.
@@ -33,7 +34,12 @@ export async function getSourcesInUse(
       Promise.all(
         RANKABLE_SOURCES.map((source) =>
           prisma.measurement
-            .findFirst({ where: { userId, source }, select: { id: true } })
+            .findFirst({
+              // A deleted reading is not data: a source whose readings were
+              // all deleted is no longer in use.
+              where: { userId, source, deletedAt: null },
+              select: { id: true },
+            })
             .then((row) => (row ? source : null)),
         ),
       ),