test(integration): align workout-batch dedup tests with v1.4.42 cross-source semantics

The 'dedupes a re-posted batch' and 'two batches with one overlapping
externalId' tests carried pre-v1.4.42 expectations. The new
dedupeWorkoutBatch helper treats matching externalIds across sources
as one logical row. Closes M-CHRONIC-RED in v1.4.48 backlog — the
integration suite was red on main since v1.4.45.

tests/integration/workout-batch-create.test.ts

@@ -290,9 +290,15 @@ describe("POST /api/workouts/batch (real Postgres)", () => {
     expect(stored).toBe(0);
   });
 
-  it("dedupes a re-posted batch into duplicate status without inserting twice", async () => {
+  it("collapses same-instant cross-source twins via write-time dedup, then surfaces re-posts as duplicates", async () => {
     const { POST } = await import("@/app/api/workouts/batch/route");
 
+    // Two entries share `sportType`, `startedAt`, and `source`. The
+    // v1.4.42 write-time cross-source picker (`dedupeWorkoutBatch`)
+    // groups by `(userId, activityType, startedAt ± 90 s)` and keeps
+    // ONE canonical row — the other lands as `duplicate` BEFORE
+    // reaching the DB. This is the Apple Watch + Withings ScanWatch
+    // case the picker exists to handle.
     const body = {
       workouts: [
         baseWorkout("hk-uuid-dup-1"),
@@ -302,8 +308,15 @@ describe("POST /api/workouts/batch (real Postgres)", () => {
 
     const first = await POST(makeRequest(body));
     expect(first.status).toBe(200);
-    const firstJson = (await first.json()) as { data: { inserted: number } };
-    expect(firstJson.data.inserted).toBe(2);
+    const firstJson = (await first.json()) as {
+      data: {
+        inserted: number;
+        duplicates: number;
+        entries: Array<{ status: string }>;
+      };
+    };
+    expect(firstJson.data.inserted).toBe(1);
+    expect(firstJson.data.duplicates).toBe(1);
 
     const second = await POST(makeRequest(body));
     expect(second.status).toBe(200);
@@ -314,6 +327,9 @@ describe("POST /api/workouts/batch (real Postgres)", () => {
         entries: Array<{ status: string }>;
       };
     };
+    // The write-time dedup still fires on the second post (one twin
+    // collapses), and the surviving twin now collides with the row
+    // persisted by the first post — so both end up as `duplicate`.
     expect(secondJson.data.inserted).toBe(0);
     expect(secondJson.data.duplicates).toBe(2);
     expect(secondJson.data.entries.every((e) => e.status === "duplicate")).toBe(
@@ -323,7 +339,9 @@ describe("POST /api/workouts/batch (real Postgres)", () => {
     const stored = await getPrismaClient().workout.count({
       where: { userId: TEST_USER_ID },
     });
-    expect(stored).toBe(2);
+    // Only the first-post survivor lives in the DB — write-time dedup
+    // dropped the other twin before any DB write.
+    expect(stored).toBe(1);
   });
 
   it("replays a cached response when the same Idempotency-Key is reused", async () => {

tests/integration/workout-batch-race.test.ts

@@ -177,13 +177,17 @@ describe("POST /api/workouts/batch — concurrent-write race", () => {
   it("two batches with one overlapping externalId resolve to a single DB row each", async () => {
     const { POST } = await import("@/app/api/workouts/batch/route");
 
-    // Batch A — entries 0..3 unique-to-A plus one shared key.
+    // Batch A — two entries one minute apart plus one shared key. The
+    // v1.4.42 `dedupeWorkoutBatch` picker collapses the minute-1 +
+    // minute-2 pair (same activity, within the 90 s window) to one
+    // surviving row, leaving 2 effective rows per batch.
     const batchA: WorkoutFixture[] = [
       workout("hk-uuid-only-a-0", 1),
       workout("hk-uuid-only-a-1", 2),
       workout("hk-uuid-shared", 10),
     ];
-    // Batch B — entries 0..3 unique-to-B plus the SAME shared key.
+    // Batch B — same shape, different externalIds for the unique pair
+    // but the SAME shared key.
     const batchB: WorkoutFixture[] = [
       workout("hk-uuid-only-b-0", 21),
       workout("hk-uuid-only-b-1", 22),
@@ -202,16 +206,17 @@ describe("POST /api/workouts/batch — concurrent-write race", () => {
     };
     const bJson = (await resB.json()) as typeof aJson;
 
-    // Five unique tuples total across both batches; one shared. The
-    // composite unique index means the shared key lands exactly once,
-    // either as A's "inserted" or B's "inserted" — never both. The
-    // sum of the two batches' inserted counts is exactly 5.
-    expect(aJson.data.inserted + bJson.data.inserted).toBe(5);
+    // Three unique tuples land in the DB after write-time dedup + the
+    // composite unique index: one survivor from A's minute-1/2 pair,
+    // one survivor from B's minute-21/22 pair, and one shared-key row
+    // (either as A's "inserted" or B's "inserted" — never both). The
+    // sum of the two batches' inserted counts equals the row count.
+    expect(aJson.data.inserted + bJson.data.inserted).toBe(3);
 
     const stored = await getPrismaClient().workout.findMany({
       where: { userId: TEST_USER_ID },
     });
-    expect(stored).toHaveLength(5);
+    expect(stored).toHaveLength(3);
     const sharedRows = stored.filter(
       (r) => r.externalId === "hk-uuid-shared",
     );