diff --git a/CHANGELOG.md b/CHANGELOG.md
index ae667caed..154891c6c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -44,6 +44,18 @@
   meaning: an app that posts only a five-point label still writes a complete
   entry, because the server derives the pleasantness value from that label.
 
+- Workouts recorded before the phone learned to send heart-rate detail can
+  pick that detail up afterwards. When the app sends a session the server
+  already holds and the payload carries the reading-by-reading heart rate
+  this time, the curve is attached to the workout that is already there and
+  shows up on its detail page. The session itself is untouched: duration,
+  calories, the average and maximum heart rate, the times, all stay as they
+  were first recorded. A workout that already has its curve is left alone,
+  so the phone can walk back through years of history as often as it likes
+  without anything being written twice. If one session's readings arrive
+  unusable, that session alone is reported back and the rest of the batch
+  still lands.
+
 ### Fixed
 
 - Marking an older missed dose as taken from the intake history now records
diff --git a/docs/api/openapi.yaml b/docs/api/openapi.yaml
index 026452bff..70132f280 100644
--- a/docs/api/openapi.yaml
+++ b/docs/api/openapi.yaml
@@ -3405,12 +3405,16 @@ paths:
       tags:
         - Measurements
       summary: Typed workout batch ingest (v1.4.25 W16b)
-      description: Server-side ingest endpoint for HKWorkout records (iOS) and Withings activity rows (server-to-server). Up
+      description: 'Server-side ingest endpoint for HKWorkout records (iOS) and Withings activity rows (server-to-server). Up
         to 100 workouts per call; nested route geometry (GeoJSON LineString) is capped at 20 000 points and stored in a
         1:1 `WorkoutRoute` row keyed by `workoutId`. Idempotent via the `Idempotency-Key` header (replay window 24h).
-        Per-entry status (`inserted | duplicate | skipped`) lets the iOS sync cursor checkpoint accurately. The request
-        body ceiling is 5 MB enforced at the HTTP layer — clients above the ceiling receive a 413 with
-        `workout.batch.payload_too_large`.
+        Per-entry status (`inserted | duplicate | enriched | skipped`) lets the iOS sync cursor checkpoint accurately.
+        An entry matching a stored workout is first-write-wins for the workout row; when it carries a `samples` array
+        and the stored workout has no heart-rate series, the series is attached and the entry reports `enriched`
+        (repeatable: a workout that already has a series is a no-op). An entry whose `samples` array fails validation is
+        refused on its own with `reason: "invalid_samples"` — the rest of the batch still lands. The request body
+        ceiling is 5 MB enforced at the HTTP layer — clients above the ceiling receive a 413 with
+        `workout.batch.payload_too_large`.'
       requestBody:
         required: true
         content:
@@ -21923,14 +21927,19 @@ components:
           type: integer
           minimum: 0
           maximum: 9007199254740991
+          description: Entries in the request. Equals `inserted + duplicates + skipped.length`.
         inserted:
           type: integer
           minimum: 0
           maximum: 9007199254740991
+          description: Workout rows this request wrote.
         duplicates:
           type: integer
           minimum: 0
           maximum: 9007199254740991
+          description: Entries that wrote no workout row because the workout was already stored. The top-level counters count
+            workout rows, so an entry reported as `enriched` counts here as well even though its heart-rate series was
+            attached.
         skipped:
           type: array
           items:
@@ -21969,8 +21978,15 @@ components:
           enum:
             - inserted
             - duplicate
+            - enriched
             - skipped
+          description: "`inserted`: a new workout row. `duplicate`: the workout was already stored and nothing was written.
+            `enriched`: the workout was already stored and the heart-rate series this entry carried was attached to it;
+            the workout row itself was not written, and the entry also counts towards the top-level `duplicates`.
+            `skipped`: the server refused the entry, see `reason`."
         reason:
+          description: "Why a `skipped` entry was refused: `unstable_external_id` for an id that does not survive a client
+            restart, `invalid_samples` for a heart-rate series that failed validation."
           type: string
       required:
         - index
diff --git a/src/app/api/workouts/__tests__/batch-create.test.ts b/src/app/api/workouts/__tests__/batch-create.test.ts
index 1b8742e5b..05a5dba93 100644
--- a/src/app/api/workouts/__tests__/batch-create.test.ts
+++ b/src/app/api/workouts/__tests__/batch-create.test.ts
@@ -23,7 +23,7 @@ vi.mock("@/lib/db", () => ({
       createMany: vi.fn(),
     },
     workoutSamples: {
-      createMany: vi.fn(),
+      createManyAndReturn: vi.fn(),
     },
     user: {
       findUnique: vi.fn(),
@@ -109,6 +109,23 @@ function makeRequest(
   });
 }
 
+/**
+ * `workout.findMany` serves two callers in this route: the pre-flight
+ * probe for rows that already exist (it passes a `where`), and — inside
+ * the fake above — the stand-in for `INSERT ... RETURNING` (`select`
+ * only). Keying on `select.id` alone stopped telling the two apart once
+ * the probe began selecting `id` so an enrichment can address the stored
+ * workout, so the RETURNING arm is the one WITHOUT a `where`.
+ */
+function mockInsertReturning(
+  rows: Array<{ id: string; source: string; externalId: string }>,
+) {
+  vi.mocked(prisma.workout.findMany).mockImplementation((async (args: {
+    where?: unknown;
+    select?: Record<string, unknown>;
+  }) => (args.where === undefined && args.select?.id ? rows : [])) as never);
+}
+
 function validWorkout(
   externalId: string,
   overrides: Record<string, unknown> = {},
@@ -161,7 +178,13 @@ beforeEach(() => {
   );
   vi.mocked(prisma.workout.findFirst).mockResolvedValue(null);
   vi.mocked(prisma.workoutRoute.createMany).mockResolvedValue({ count: 0 });
-  vi.mocked(prisma.workoutSamples.createMany).mockResolvedValue({ count: 0 });
+  // The series write reports which rows landed, so an enrichment can tell
+  // an attach from a row a concurrent writer got in first. The fake
+  // echoes every row back as landed.
+  vi.mocked(prisma.workoutSamples.createManyAndReturn).mockImplementation(
+    (async (args: { data: Array<{ workoutId: string }> }) =>
+      args.data.map((row) => ({ workoutId: row.workoutId }))) as never,
+  );
   // v1.4.43 W9 — default to no per-user source-priority override so
   // the write-time picker walks the canonical default ladder. Tests
   // that exercise a custom ladder override this in-line.
@@ -434,25 +457,18 @@ describe("POST /api/workouts/batch — per-entry status envelope", () => {
         createdAt: new Date("2026-05-14T10:00:01.000Z"),
       },
     ] as never);
-    vi.mocked(prisma.workout.findMany).mockImplementation((async (args: {
-      select?: Record<string, unknown>;
-    }) => {
-      if (args.select?.id) {
-        return [
-          {
-            id: "apple-id",
-            source: "APPLE_HEALTH",
-            externalId: "shared-external-id",
-          },
-          {
-            id: "manual-id",
-            source: "MANUAL",
-            externalId: "shared-external-id",
-          },
-        ];
-      }
-      return [];
-    }) as never);
+    mockInsertReturning([
+      {
+        id: "apple-id",
+        source: "APPLE_HEALTH",
+        externalId: "shared-external-id",
+      },
+      {
+        id: "manual-id",
+        source: "MANUAL",
+        externalId: "shared-external-id",
+      },
+    ]);
 
     const res = await POST(
       makeRequest({
@@ -480,20 +496,13 @@ describe("POST /api/workouts/batch — nested route attachment", () => {
     vi.mocked(prisma.workout.createMany).mockResolvedValue({ count: 1 });
     // Post-insert lookup returns the newly-inserted workout id so the
     // route can be attached by FK.
-    vi.mocked(prisma.workout.findMany).mockImplementation((async (args: {
-      select?: { id?: true; source?: true; externalId?: true };
-    }) => {
-      if (args.select?.id) {
-        return [
-          {
-            id: "wkt-fresh-id",
-            source: "APPLE_HEALTH",
-            externalId: "uuid-with-route",
-          },
-        ];
-      }
-      return [];
-    }) as never);
+    mockInsertReturning([
+      {
+        id: "wkt-fresh-id",
+        source: "APPLE_HEALTH",
+        externalId: "uuid-with-route",
+      },
+    ]);
 
     const res = await POST(
       makeRequest({
@@ -523,20 +532,13 @@ describe("POST /api/workouts/batch — nested route attachment", () => {
 describe("POST /api/workouts/batch — per-workout HR series (v1.10.0)", () => {
   it("creates a WorkoutSamples row for an indoor workout (samples, no route)", async () => {
     vi.mocked(prisma.workout.createMany).mockResolvedValue({ count: 1 });
-    vi.mocked(prisma.workout.findMany).mockImplementation((async (args: {
-      select?: { id?: true };
-    }) => {
-      if (args.select?.id) {
-        return [
-          {
-            id: "wkt-indoor-id",
-            source: "APPLE_HEALTH",
-            externalId: "uuid-indoor",
-          },
-        ];
-      }
-      return [];
-    }) as never);
+    mockInsertReturning([
+      {
+        id: "wkt-indoor-id",
+        source: "APPLE_HEALTH",
+        externalId: "uuid-indoor",
+      },
+    ]);
 
     const res = await POST(
       makeRequest({
@@ -556,8 +558,9 @@ describe("POST /api/workouts/batch — per-workout HR series (v1.10.0)", () => {
     // The route table is untouched — an indoor workout has no GPS route.
     expect(prisma.workoutRoute.createMany).not.toHaveBeenCalled();
     // The HR series lands in the dedicated child table by FK.
-    expect(prisma.workoutSamples.createMany).toHaveBeenCalledTimes(1);
-    const call = vi.mocked(prisma.workoutSamples.createMany).mock.calls[0]?.[0];
+    expect(prisma.workoutSamples.createManyAndReturn).toHaveBeenCalledTimes(1);
+    const call = vi.mocked(prisma.workoutSamples.createManyAndReturn).mock
+      .calls[0]?.[0];
     const rows = (
       call as {
         data: Array<{
@@ -575,20 +578,13 @@ describe("POST /api/workouts/batch — per-workout HR series (v1.10.0)", () => {
 
   it("attaches both a route and an HR series on one workout", async () => {
     vi.mocked(prisma.workout.createMany).mockResolvedValue({ count: 1 });
-    vi.mocked(prisma.workout.findMany).mockImplementation((async (args: {
-      select?: { id?: true };
-    }) => {
-      if (args.select?.id) {
-        return [
-          {
-            id: "wkt-both-id",
-            source: "APPLE_HEALTH",
-            externalId: "uuid-both",
-          },
-        ];
-      }
-      return [];
-    }) as never);
+    mockInsertReturning([
+      {
+        id: "wkt-both-id",
+        source: "APPLE_HEALTH",
+        externalId: "uuid-both",
+      },
+    ]);
 
     const res = await POST(
       makeRequest({
@@ -610,14 +606,15 @@ describe("POST /api/workouts/batch — per-workout HR series (v1.10.0)", () => {
     );
     expect(res.status).toBe(200);
     expect(prisma.workoutRoute.createMany).toHaveBeenCalledTimes(1);
-    expect(prisma.workoutSamples.createMany).toHaveBeenCalledTimes(1);
+    expect(prisma.workoutSamples.createManyAndReturn).toHaveBeenCalledTimes(1);
     const routeRows = (
       vi.mocked(prisma.workoutRoute.createMany).mock.calls[0]?.[0] as {
         data: Array<{ workoutId: string }>;
       }
     ).data;
     const sampleRows = (
-      vi.mocked(prisma.workoutSamples.createMany).mock.calls[0]?.[0] as {
+      vi.mocked(prisma.workoutSamples.createManyAndReturn).mock
+        .calls[0]?.[0] as {
         data: Array<{ workoutId: string }>;
       }
     ).data;
@@ -632,7 +629,7 @@ describe("POST /api/workouts/batch — per-workout HR series (v1.10.0)", () => {
       makeRequest({ workouts: [validWorkout("uuid-no-series")] }),
     );
     expect(res.status).toBe(200);
-    expect(prisma.workoutSamples.createMany).not.toHaveBeenCalled();
+    expect(prisma.workoutSamples.createManyAndReturn).not.toHaveBeenCalled();
   });
 });
 
diff --git a/src/app/api/workouts/batch/route.ts b/src/app/api/workouts/batch/route.ts
index ac9f1c65d..61cfec22c 100644
--- a/src/app/api/workouts/batch/route.ts
+++ b/src/app/api/workouts/batch/route.ts
@@ -30,8 +30,8 @@
  *   - `Content-Length` ceiling at 5 MB before parsing — anything
  *     larger returns 413 so the iOS client falls back to one workout
  *     per call.
- *   - Per-entry status (`inserted | duplicate | skipped`) so the iOS
- *     sync cursor can checkpoint accurately.
+ *   - Per-entry status (`inserted | duplicate | enriched | skipped`) so
+ *     the iOS sync cursor can checkpoint accurately.
  *
  * Idempotency contract:
  *   - HTTP-level via `Idempotency-Key` (replays cached envelope).
@@ -39,6 +39,13 @@
  *     composite index. Re-posting the same batch surfaces duplicates
  *     rather than failing the call.
  *
+ * Heart-rate series enrichment: a re-post that matches a stored
+ * workout and carries a `samples` array attaches that series when the
+ * workout has none. The workout row itself stays first-write-wins —
+ * nothing on it is written, not one column — and a workout that already
+ * holds a series is a no-op, so the client's history sweep is repeatable
+ * as often as it likes. See the enrichment block below.
+ *
  * Race reconciliation uses PostgreSQL's `INSERT ... RETURNING` through
  * Prisma's `createManyAndReturn`. The returned composite keys identify the
  * exact rows this request inserted, so per-entry statuses, child rows, and
@@ -66,10 +73,11 @@ import { checkRateLimit } from "@/lib/rate-limit";
 import { enqueuePrDetection } from "@/lib/jobs/pr-detection";
 import { invalidateUserMeasurements } from "@/lib/cache/invalidate";
 import { emitDataArrival } from "@/lib/arrivals/emit-shared";
+import { MAX_WORKOUTS_PER_BATCH } from "@/lib/validations/workout";
 import {
-  createBatchWorkoutSchema,
-  MAX_WORKOUTS_PER_BATCH,
-} from "@/lib/validations/workout";
+  INVALID_SAMPLES_REASON,
+  parseWorkoutBatch,
+} from "@/lib/workouts/batch-ingest-parse";
 import {
   classifyExternalId,
   unstableExternalIdMeta,
@@ -106,16 +114,14 @@ const MAX_BODY_BYTES = 5 * 1024 * 1024;
 
 /**
  * Per-entry outcome the iOS client uses to advance its sync cursor.
- * `inserted` and `duplicate` both indicate the row landed (or was
- * already present); the client can checkpoint past them identically.
- * `skipped` covers entries the server cannot durably store — currently
- * unused by this endpoint (the Zod schema rejects malformed entries
- * with a 422 before we reach the per-entry pass), but reserved on the
- * envelope so the response shape parallels the measurements batch and
- * future server-side validation can surface fine-grained skips without
- * breaking the iOS DTO.
+ * `inserted`, `duplicate` and `enriched` all indicate the row landed (or
+ * was already present); the client can checkpoint past them identically.
+ * `enriched` additionally says the entry's heart-rate series was attached
+ * to a workout that had none, which is what lets a history sweep count
+ * its own progress. `skipped` covers entries the server refused: an
+ * unusable external id, or a `samples` array that failed validation.
  */
-type EntryStatus = "inserted" | "duplicate" | "skipped";
+type EntryStatus = "inserted" | "duplicate" | "enriched" | "skipped";
 interface EntryResult {
   index: number;
   status: EntryStatus;
@@ -251,15 +257,18 @@ async function postBatch(request: NextRequest): Promise<Response> {
     );
   }
 
-  const parsed = createBatchWorkoutSchema.safeParse(rawBody);
-  if (!parsed.success) {
-    const issue = parsed.error.issues[0];
-    return apiError(issue?.message ?? "Invalid batch", 400, {
+  // Strict on every field, per-entry on `samples` alone — see
+  // `parseWorkoutBatch` for why the series is the one field whose
+  // failure must not take the rest of a history sweep down with it.
+  const parsed = parseWorkoutBatch(rawBody);
+  if (!parsed.ok) {
+    return apiError(parsed.message, 400, {
       errorCode: "workout.batch.invalid",
     });
   }
 
   const { workouts } = parsed.data;
+  const refusedSampleIndices = new Set(parsed.refusedSampleIndices);
 
   // Pre-flight duplicate detection so we can return per-entry status.
   // The composite unique index is `(userId, source, externalId)` —
@@ -289,6 +298,18 @@ async function postBatch(request: NextRequest): Promise<Response> {
   const results: EntryResult[] = new Array(workouts.length);
   const unstableShapes: UnstableExternalIdShape[] = [];
   const prepared: Prepared[] = workouts.flatMap((w, index) => {
+    // An entry whose series failed validation is refused whole. Storing
+    // the workout without the curve the caller asked us to keep would be
+    // a silent loss, and the row may well already exist anyway.
+    if (refusedSampleIndices.has(index)) {
+      results[index] = {
+        index,
+        status: "skipped",
+        reason: INVALID_SAMPLES_REASON,
+      };
+      return [];
+    }
+
     // The `(userId, source, externalId)` dedup key is only idempotent
     // while the id is STABLE across client launches. An id that rotates
     // per process (an object description carrying a memory address)
@@ -408,6 +429,7 @@ async function postBatch(request: NextRequest): Promise<Response> {
   const survivors = prepared.filter((p) => survivingIndices.has(p.index));
   let duplicateCount = droppedByWriteDedup.length;
   let insertedCount = 0;
+  let enrichedCount = 0;
   const insertedIdByIndex = new Map<number, string>();
 
   if (survivors.length > 0) {
@@ -418,6 +440,9 @@ async function postBatch(request: NextRequest): Promise<Response> {
       .map((p) => p.dedupKey)
       .filter((k): k is { source: string; externalId: string } => k !== null);
 
+    // The same probe answers both questions: does the row exist, and
+    // does it already carry a series. `id` comes along so an enrichment
+    // can address the stored workout without a second round trip.
     const existing = dedupCandidates.length
       ? await prisma.workout.findMany({
           where: {
@@ -427,30 +452,65 @@ async function postBatch(request: NextRequest): Promise<Response> {
               externalId: k.externalId,
             })),
           },
-          select: { source: true, externalId: true },
+          select: {
+            id: true,
+            source: true,
+            externalId: true,
+            samples: { select: { workoutId: true } },
+          },
         })
       : [];
 
-    const existingSet = new Set(
-      existing.map((row) => `${row.source}::${row.externalId}`),
-    );
+    const existingByKey = new Map<string, { id: string; hasSeries: boolean }>();
+    for (const row of existing) {
+      if (row.externalId === null) continue;
+      existingByKey.set(`${row.source}::${row.externalId}`, {
+        id: row.id,
+        hasSeries: row.samples !== null,
+      });
+    }
 
     const toInsert: Prepared[] = [];
+    /** Stored workouts this batch hands a heart-rate series to. */
+    const toEnrich: Array<{
+      index: number;
+      workoutId: string;
+      samples: NonNullable<Prepared["samples"]>;
+    }> = [];
+    /** Workouts already claimed by an earlier entry of THIS batch. */
+    const enrichClaimed = new Set<string>();
     for (const p of survivors) {
       const keyTuple = p.dedupKey
         ? `${p.dedupKey.source}::${p.dedupKey.externalId}`
         : null;
-      if (keyTuple !== null && existingSet.has(keyTuple)) {
-        results[p.index] = { index: p.index, status: "duplicate" };
-        duplicateCount += 1;
+      const known = keyTuple !== null ? existingByKey.get(keyTuple) : undefined;
+      if (known) {
+        if (p.samples && !known.hasSeries && !enrichClaimed.has(known.id)) {
+          enrichClaimed.add(known.id);
+          // Enrichment. The status is assigned after the write, because
+          // a concurrent writer may get the series in first — in which
+          // case this entry is the plain duplicate it always was. A
+          // second entry of this batch naming the same workout takes the
+          // duplicate arm above: one workout, one series, one `enriched`.
+          toEnrich.push({
+            index: p.index,
+            workoutId: known.id,
+            samples: p.samples,
+          });
+        } else {
+          results[p.index] = { index: p.index, status: "duplicate" };
+          duplicateCount += 1;
+        }
       } else {
         results[p.index] = { index: p.index, status: "inserted" };
         toInsert.push(p);
       }
     }
 
-    if (toInsert.length > 0) {
+    if (toInsert.length > 0 || toEnrich.length > 0) {
       const CHUNK = 100;
+      /** Workout ids whose series row this request actually wrote. */
+      const seriesLanded = new Set<string>();
 
       await prisma.$transaction(async (tx) => {
         const withExternalId = toInsert.filter((p) => p.dedupKey !== null);
@@ -517,6 +577,19 @@ async function postBatch(request: NextRequest): Promise<Response> {
           }
         }
 
+        // Enrichment rides the SAME child write as a fresh workout's
+        // series — one mechanism, one place where a series is stored.
+        // The only difference is where the `workoutId` came from: the
+        // pre-flight probe instead of this request's INSERT ... RETURNING.
+        // Nothing here writes to the workout row.
+        for (const e of toEnrich) {
+          samplesToInsert.push({
+            workoutId: e.workoutId,
+            samples: e.samples.samples as Prisma.InputJsonValue,
+            sampleCount: e.samples.sampleCount,
+          });
+        }
+
         for (let i = 0; i < routesToInsert.length; i += CHUNK) {
           await tx.workoutRoute.createMany({
             data: routesToInsert.slice(i, i + CHUNK),
@@ -524,10 +597,16 @@ async function postBatch(request: NextRequest): Promise<Response> {
           });
         }
         for (let i = 0; i < samplesToInsert.length; i += CHUNK) {
-          await tx.workoutSamples.createMany({
+          // RETURNING names the rows that actually landed. `workoutId` is
+          // unique, so a workout that gained a series between the probe
+          // and this write is skipped here and reports as a duplicate —
+          // the re-post stays a no-op and never overwrites a stored curve.
+          const landed = await tx.workoutSamples.createManyAndReturn({
             data: samplesToInsert.slice(i, i + CHUNK),
             skipDuplicates: true,
+            select: { workoutId: true },
           });
+          for (const row of landed) seriesLanded.add(row.workoutId);
         }
       });
 
@@ -540,6 +619,18 @@ async function postBatch(request: NextRequest): Promise<Response> {
           duplicateCount += 1;
         }
       }
+
+      // An enriched entry is still a duplicate of the workout row: the
+      // top-level counters count rows, and no row was inserted for it.
+      // The per-entry status carries what happened to the series.
+      for (const e of toEnrich) {
+        results[e.index] = {
+          index: e.index,
+          status: seriesLanded.has(e.workoutId) ? "enriched" : "duplicate",
+        };
+        if (seriesLanded.has(e.workoutId)) enrichedCount += 1;
+        duplicateCount += 1;
+      }
     }
   }
 
@@ -554,6 +645,7 @@ async function postBatch(request: NextRequest): Promise<Response> {
       processed: workouts.length,
       inserted: insertedCount,
       duplicates: duplicateCount,
+      enriched: enrichedCount,
       skipped: skipped.length,
     },
   });
@@ -584,12 +676,14 @@ async function postBatch(request: NextRequest): Promise<Response> {
     }
   }
 
+  // Counts only. The series itself never reaches a wide event.
   annotate({
     action: { name: "workout.batch.ingest" },
     meta: {
       processed: workouts.length,
       inserted: insertedCount,
       duplicates: duplicateCount,
+      enriched: enrichedCount,
       skipped: skipped.length,
     },
   });
@@ -598,11 +692,17 @@ async function postBatch(request: NextRequest): Promise<Response> {
   // caches when at least one row landed. Workouts ride on the
   // measurements bucket because achievements / analytics also touch
   // workout-derived metrics.
-  if (insertedCount > 0) {
+  // An enrichment changes what the workout reads as — the detail seam
+  // gains its curve, the list gains its glyph — so it busts the cache
+  // too, even though no workout row was written.
+  if (insertedCount > 0 || enrichedCount > 0) {
     invalidateUserMeasurements(user.id);
+  }
 
+  if (insertedCount > 0) {
     // One arrival per exact INSERT ... RETURNING winner. Historical rows still
     // stop at the shared salience classifier before any queue work.
+    // An enrichment raises none: the workout arrived when it was stored.
     void emitWorkoutArrivals(user.id, prepared, insertedIdByIndex).catch(
       () => {},
     );
diff --git a/src/lib/openapi/routes/workouts.ts b/src/lib/openapi/routes/workouts.ts
index 9c4b2f910..42b312b27 100644
--- a/src/lib/openapi/routes/workouts.ts
+++ b/src/lib/openapi/routes/workouts.ts
@@ -20,22 +20,55 @@ import {
 
 // v1.4.25 W16b — typed workout batch ingest response envelope. Mirrors
 // the measurements batch shape but reports the `workouts` count rather
-// than the entries count, and the `skipped` field is reserved (the
-// Zod schema rejects malformed entries with a 400 before the per-entry
-// pass, so today's responses always carry an empty array).
+// than the entries count. `skipped` carries the entries the server
+// refused: an unusable external id, or a `samples` array that failed
+// validation (`reason: "invalid_samples"`).
+//
+// `enriched` says the entry matched a stored workout that had no
+// heart-rate series and the series it carried was attached. The
+// workout row itself was not written, so such an entry also counts
+// towards `duplicates`. That rule is part of the published contract,
+// not just a note here: it rides the field descriptions below, because
+// a client summing the counters has to know which bucket an
+// enrichment lands in.
 const workoutBatchEntryResult = z
   .object({
     index: z.number().int().nonnegative(),
-    status: z.enum(["inserted", "duplicate", "skipped"]),
-    reason: z.string().optional(),
+    status: z
+      .enum(["inserted", "duplicate", "enriched", "skipped"])
+      .describe(
+        "`inserted`: a new workout row. `duplicate`: the workout was already stored and nothing was written. `enriched`: the workout was already stored and the heart-rate series this entry carried was attached to it; the workout row itself was not written, and the entry also counts towards the top-level `duplicates`. `skipped`: the server refused the entry, see `reason`.",
+      ),
+    reason: z
+      .string()
+      .optional()
+      .describe(
+        "Why a `skipped` entry was refused: `unstable_external_id` for an id that does not survive a client restart, `invalid_samples` for a heart-rate series that failed validation.",
+      ),
   })
   .meta({ id: "WorkoutBatchEntryResult" });
 
 const workoutBatchResponse = z
   .object({
-    processed: z.number().int().nonnegative(),
-    inserted: z.number().int().nonnegative(),
-    duplicates: z.number().int().nonnegative(),
+    processed: z
+      .number()
+      .int()
+      .nonnegative()
+      .describe(
+        "Entries in the request. Equals `inserted + duplicates + skipped.length`.",
+      ),
+    inserted: z
+      .number()
+      .int()
+      .nonnegative()
+      .describe("Workout rows this request wrote."),
+    duplicates: z
+      .number()
+      .int()
+      .nonnegative()
+      .describe(
+        "Entries that wrote no workout row because the workout was already stored. The top-level counters count workout rows, so an entry reported as `enriched` counts here as well even though its heart-rate series was attached.",
+      ),
     skipped: z.array(
       z.object({
         index: z.number().int().nonnegative(),
@@ -275,7 +308,7 @@ export const workoutPaths: NonNullable<ZodOpenApiObject["paths"]> = {
       tags: ["Measurements"],
       summary: "Typed workout batch ingest (v1.4.25 W16b)",
       description:
-        "Server-side ingest endpoint for HKWorkout records (iOS) and Withings activity rows (server-to-server). Up to 100 workouts per call; nested route geometry (GeoJSON LineString) is capped at 20 000 points and stored in a 1:1 `WorkoutRoute` row keyed by `workoutId`. Idempotent via the `Idempotency-Key` header (replay window 24h). Per-entry status (`inserted | duplicate | skipped`) lets the iOS sync cursor checkpoint accurately. The request body ceiling is 5 MB enforced at the HTTP layer — clients above the ceiling receive a 413 with `workout.batch.payload_too_large`.",
+        'Server-side ingest endpoint for HKWorkout records (iOS) and Withings activity rows (server-to-server). Up to 100 workouts per call; nested route geometry (GeoJSON LineString) is capped at 20 000 points and stored in a 1:1 `WorkoutRoute` row keyed by `workoutId`. Idempotent via the `Idempotency-Key` header (replay window 24h). Per-entry status (`inserted | duplicate | enriched | skipped`) lets the iOS sync cursor checkpoint accurately. An entry matching a stored workout is first-write-wins for the workout row; when it carries a `samples` array and the stored workout has no heart-rate series, the series is attached and the entry reports `enriched` (repeatable: a workout that already has a series is a no-op). An entry whose `samples` array fails validation is refused on its own with `reason: "invalid_samples"` — the rest of the batch still lands. The request body ceiling is 5 MB enforced at the HTTP layer — clients above the ceiling receive a 413 with `workout.batch.payload_too_large`.',
       requestBody: {
         required: true,
         content: { "application/json": { schema: createBatchWorkoutSchema } },
diff --git a/src/lib/workouts/__tests__/batch-ingest-parse.test.ts b/src/lib/workouts/__tests__/batch-ingest-parse.test.ts
new file mode 100644
index 000000000..7be52ce3d
--- /dev/null
+++ b/src/lib/workouts/__tests__/batch-ingest-parse.test.ts
@@ -0,0 +1,70 @@
+import { describe, expect, it } from "vitest";
+
+import {
+  INVALID_SAMPLES_REASON,
+  parseWorkoutBatch,
+} from "@/lib/workouts/batch-ingest-parse";
+
+function entry(overrides: Record<string, unknown> = {}) {
+  return {
+    sportType: "running",
+    startedAt: "2026-05-14T06:30:00.000Z",
+    endedAt: "2026-05-14T07:15:00.000Z",
+    source: "APPLE_HEALTH",
+    externalId: "hk-uuid-1",
+    ...overrides,
+  };
+}
+
+describe("parseWorkoutBatch", () => {
+  it("parses a clean batch and refuses nothing", () => {
+    const result = parseWorkoutBatch({
+      workouts: [
+        entry({ samples: [{ t: "2026-05-14T06:30:00.000Z", hr: 120 }] }),
+      ],
+    });
+    expect(result.ok).toBe(true);
+    if (!result.ok) return;
+    expect(result.refusedSampleIndices).toEqual([]);
+    expect(result.data.workouts[0]?.samples).toHaveLength(1);
+  });
+
+  it("refuses only the entries whose samples array is malformed", () => {
+    const result = parseWorkoutBatch({
+      workouts: [
+        entry({ externalId: "hk-a", samples: [{ t: "nope", hr: 4000 }] }),
+        entry({ externalId: "hk-b" }),
+        entry({ externalId: "hk-c", samples: [] }),
+      ],
+    });
+    expect(result.ok).toBe(true);
+    if (!result.ok) return;
+    expect(result.refusedSampleIndices).toEqual([0, 2]);
+    // The survivors keep their full typed shape.
+    expect(result.data.workouts).toHaveLength(3);
+    expect(result.data.workouts[1]?.externalId).toBe("hk-b");
+    expect(result.data.workouts[0]?.samples).toBeUndefined();
+  });
+
+  it("keeps failing the whole batch when any other field is wrong", () => {
+    const result = parseWorkoutBatch({
+      workouts: [
+        entry({ endedAt: "2026-05-14T06:00:00.000Z" }),
+        entry({ externalId: "hk-b", samples: [{ t: "nope" }] }),
+      ],
+    });
+    expect(result.ok).toBe(false);
+    if (result.ok) return;
+    expect(result.message).toMatch(/endedAt/i);
+  });
+
+  it("fails the batch when the envelope itself is not a batch", () => {
+    expect(parseWorkoutBatch({ workouts: [] }).ok).toBe(false);
+    expect(parseWorkoutBatch(null).ok).toBe(false);
+    expect(parseWorkoutBatch({ workouts: "nope" }).ok).toBe(false);
+  });
+
+  it("names the per-entry reason code the route reports", () => {
+    expect(INVALID_SAMPLES_REASON).toBe("invalid_samples");
+  });
+});
diff --git a/src/lib/workouts/batch-ingest-parse.ts b/src/lib/workouts/batch-ingest-parse.ts
new file mode 100644
index 000000000..56b9ac7cf
--- /dev/null
+++ b/src/lib/workouts/batch-ingest-parse.ts
@@ -0,0 +1,109 @@
+/**
+ * Batch-ingest body parsing for `POST /api/workouts/batch`.
+ *
+ * The wire contract is `createBatchWorkoutSchema` and stays exactly that:
+ * this module never widens what the endpoint accepts. What it changes is
+ * WHERE one specific failure lands.
+ *
+ * A malformed field anywhere in the batch fails the whole call with a 400,
+ * which is right for a client that got the shape wrong. The `samples`
+ * array is the exception, because of how it arrives: the native client
+ * re-posts workouts the server already stores purely to hand over their
+ * heart-rate curve, sweeping years of history in batches of up to a
+ * hundred. One session whose series came out of HealthKit malformed would
+ * otherwise stall the entire sweep at a 400 the client cannot repair by
+ * retrying — every other workout in that batch is fine and has nothing to
+ * do with the bad one.
+ *
+ * So an entry whose `samples` array fails validation is refused on its
+ * own, exactly the way an entry with an unusable `externalId` already is
+ * (see `classifyExternalId` in the route), and the rest of the batch
+ * lands. The refused entry is NOT stripped down and stored without its
+ * series: the caller asked for the curve to be saved, so a half-write
+ * would be a silent loss. It is reported back with its index so the
+ * client knows which session to fix.
+ *
+ * Every other validation failure keeps failing the batch.
+ */
+import {
+  createBatchWorkoutSchema,
+  type CreateBatchWorkoutInput,
+} from "@/lib/validations/workout";
+
+/** Per-entry `reason` code for a `samples` array that failed validation. */
+export const INVALID_SAMPLES_REASON = "invalid_samples";
+
+export type WorkoutBatchParseResult =
+  | {
+      ok: true;
+      data: CreateBatchWorkoutInput;
+      /** Batch indices whose `samples` array was refused. */
+      refusedSampleIndices: number[];
+    }
+  | { ok: false; message: string };
+
+function isRecord(value: unknown): value is Record<string, unknown> {
+  return typeof value === "object" && value !== null && !Array.isArray(value);
+}
+
+/**
+ * Indices of entries whose ONLY problem is the `samples` array. An issue
+ * path of `["workouts", 3, "samples", ...]` names entry 3; anything else
+ * means the batch is broken in a way this path does not forgive.
+ */
+function collectSampleFailureIndices(
+  issues: ReadonlyArray<{ path: PropertyKey[] }>,
+): number[] | null {
+  const indices = new Set<number>();
+  for (const issue of issues) {
+    const [root, index, field] = issue.path;
+    if (root !== "workouts" || typeof index !== "number" || field !== "samples")
+      return null;
+    indices.add(index);
+  }
+  return indices.size > 0 ? [...indices].sort((a, b) => a - b) : null;
+}
+
+/**
+ * Parses a batch body, refusing per entry when the only failures are
+ * `samples` arrays. On that path the offending entries are re-parsed
+ * without their series so the surviving entries keep their fully typed
+ * shape; the caller drops the refused indices before any write.
+ */
+export function parseWorkoutBatch(rawBody: unknown): WorkoutBatchParseResult {
+  const strict = createBatchWorkoutSchema.safeParse(rawBody);
+  if (strict.success) {
+    return { ok: true, data: strict.data, refusedSampleIndices: [] };
+  }
+
+  const refusedSampleIndices = collectSampleFailureIndices(strict.error.issues);
+  if (
+    refusedSampleIndices === null ||
+    !isRecord(rawBody) ||
+    !Array.isArray(rawBody.workouts)
+  ) {
+    return {
+      ok: false,
+      message: strict.error.issues[0]?.message ?? "Invalid batch",
+    };
+  }
+
+  const refused = new Set(refusedSampleIndices);
+  const stripped = {
+    ...rawBody,
+    workouts: rawBody.workouts.map((entry, index) => {
+      if (!refused.has(index) || !isRecord(entry)) return entry;
+      const { samples: _samples, ...rest } = entry;
+      return rest;
+    }),
+  };
+
+  const relaxed = createBatchWorkoutSchema.safeParse(stripped);
+  if (!relaxed.success) {
+    return {
+      ok: false,
+      message: relaxed.error.issues[0]?.message ?? "Invalid batch",
+    };
+  }
+  return { ok: true, data: relaxed.data, refusedSampleIndices };
+}
diff --git a/tests/integration/workout-batch-enrich.test.ts b/tests/integration/workout-batch-enrich.test.ts
new file mode 100644
index 000000000..3b80f526e
--- /dev/null
+++ b/tests/integration/workout-batch-enrich.test.ts
@@ -0,0 +1,460 @@
+/**
+ * Integration suite for the heart-rate series enrichment path of
+ * `POST /api/workouts/batch`, against a real Postgres in a testcontainer.
+ *
+ * The case: the native client posted a workout before it learned to send
+ * the per-workout HR series. The row exists, the curve does not. A later
+ * re-post of the SAME `(source, externalId)` carrying a `samples` array
+ * attaches the series to the stored workout and reports the entry as
+ * `enriched`.
+ *
+ * What the suite pins:
+ *   - The attach happens once and reports `enriched`
+ *   - A second re-post over an existing series is a no-op and never
+ *     reports `enriched` twice
+ *   - The workout row is byte-identical across the enrichment — every
+ *     column, `updatedAt` included, compared as a whole row
+ *   - A malformed `samples` array is refused per entry; the rest of the
+ *     batch still lands
+ *   - A batch mixing insert / enrich / duplicate / skip reports each
+ *     entry with its own status
+ */
+import { NextRequest } from "next/server";
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+import { cookieJar, headerJar } from "./mock-next-headers";
+import { getPrismaClient, truncateAllTables } from "./setup";
+
+process.env.API_TOKEN_HMAC_KEY ??=
+  "test-hmac-key-workout-enrich-integration-32-bytes-min-1234567890";
+process.env.ENCRYPTION_KEY =
+  "0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef";
+
+const TEST_USER_ID = "user-workout-enrich-test";
+
+vi.mock("next/headers", async () => {
+  const { cookieJar, headerJar } = await import("./mock-next-headers");
+  return {
+    headers: vi.fn(async () => ({
+      get: (name: string) => headerJar.get(name.toLowerCase()) ?? null,
+    })),
+    cookies: vi.fn(async () => ({
+      get: (name: string) => {
+        const value = cookieJar.get(name);
+        return value ? { name, value } : undefined;
+      },
+      set: (name: string, value: string) => {
+        cookieJar.set(name, value);
+      },
+      delete: (name: string) => {
+        cookieJar.delete(name);
+      },
+    })),
+  };
+});
+
+vi.mock("@/lib/db-compat", () => ({
+  ensureDbCompatibility: vi.fn().mockResolvedValue(undefined),
+}));
+
+beforeEach(async () => {
+  await truncateAllTables(getPrismaClient());
+  cookieJar.clear();
+  headerJar.clear();
+  await getPrismaClient().user.create({
+    data: {
+      id: TEST_USER_ID,
+      username: "workout-enrich",
+      email: "workout-enrich@example.test",
+    },
+  });
+  const session = await getPrismaClient().session.create({
+    data: {
+      userId: TEST_USER_ID,
+      expiresAt: new Date(Date.now() + 60 * 60 * 1000),
+    },
+  });
+  cookieJar.set("healthlog_session", session.id);
+});
+
+interface WorkoutFixture {
+  sportType?: string;
+  startedAt?: string;
+  endedAt?: string;
+  totalEnergyKcal?: number;
+  totalDistanceM?: number;
+  avgHeartRate?: number;
+  maxHeartRate?: number;
+  minHeartRate?: number;
+  source?: string;
+  externalId?: string;
+  metadata?: Record<string, unknown>;
+  samples?: unknown;
+}
+
+interface BatchResponse {
+  processed: number;
+  inserted: number;
+  duplicates: number;
+  skipped: Array<{ index: number; reason: string }>;
+  entries: Array<{ index: number; status: string; reason?: string }>;
+}
+
+function makeRequest(body: { workouts: WorkoutFixture[] }): NextRequest {
+  return new NextRequest("http://localhost/api/workouts/batch", {
+    method: "POST",
+    headers: { "content-type": "application/json" },
+    body: JSON.stringify(body),
+  });
+}
+
+function baseWorkout(
+  externalId: string,
+  overrides: WorkoutFixture = {},
+): WorkoutFixture {
+  return {
+    sportType: "running",
+    startedAt: "2026-05-14T06:30:00.000Z",
+    endedAt: "2026-05-14T07:15:00.000Z",
+    source: "APPLE_HEALTH",
+    externalId,
+    ...overrides,
+  };
+}
+
+const SERIES = [
+  { t: "2026-05-14T06:30:00.000Z", hr: 121 },
+  { t: "2026-05-14T06:30:05.000Z", hr: 128, cadence: 168 },
+  { t: "2026-05-14T06:30:10.000Z", hr: 133 },
+];
+
+async function post(body: {
+  workouts: WorkoutFixture[];
+}): Promise<{ status: number; data: BatchResponse }> {
+  const { POST } = await import("@/app/api/workouts/batch/route");
+  const res = await POST(makeRequest(body));
+  const json = (await res.json()) as { data: BatchResponse };
+  return { status: res.status, data: json.data };
+}
+
+describe("POST /api/workouts/batch — HR series enrichment (real Postgres)", () => {
+  it("attaches the series to a stored workout that has none and reports enriched", async () => {
+    const first = await post({
+      workouts: [baseWorkout("hk-uuid-enrich-001")],
+    });
+    expect(first.status).toBe(200);
+    expect(first.data.inserted).toBe(1);
+    expect(
+      await getPrismaClient().workoutSamples.count({
+        where: { workout: { userId: TEST_USER_ID } },
+      }),
+    ).toBe(0);
+
+    const second = await post({
+      workouts: [baseWorkout("hk-uuid-enrich-001", { samples: SERIES })],
+    });
+    expect(second.status).toBe(200);
+    expect(second.data.inserted).toBe(0);
+    expect(second.data.entries).toEqual([{ index: 0, status: "enriched" }]);
+
+    const stored = await getPrismaClient().workout.findFirst({
+      where: { userId: TEST_USER_ID, externalId: "hk-uuid-enrich-001" },
+      include: { samples: true },
+    });
+    expect(stored?.samples).not.toBeNull();
+    expect(stored?.samples?.sampleCount).toBe(3);
+    expect(stored?.samples?.samples).toEqual(SERIES);
+
+    // The workout row count is unchanged — enrichment never mints a row.
+    expect(
+      await getPrismaClient().workout.count({
+        where: { userId: TEST_USER_ID },
+      }),
+    ).toBe(1);
+  });
+
+  it("treats a re-post over an existing series as a no-op and never reports enriched twice", async () => {
+    await post({ workouts: [baseWorkout("hk-uuid-enrich-002")] });
+    const enriching = await post({
+      workouts: [baseWorkout("hk-uuid-enrich-002", { samples: SERIES })],
+    });
+    expect(enriching.data.entries[0]?.status).toBe("enriched");
+
+    const storedSeries = await getPrismaClient().workoutSamples.findFirst({
+      where: { workout: { externalId: "hk-uuid-enrich-002" } },
+    });
+    expect(storedSeries).not.toBeNull();
+
+    const again = await post({
+      workouts: [
+        baseWorkout("hk-uuid-enrich-002", {
+          samples: [
+            ...SERIES,
+            { t: "2026-05-14T06:30:15.000Z", hr: 141 },
+            { t: "2026-05-14T06:30:20.000Z", hr: 145 },
+          ],
+        }),
+      ],
+    });
+    expect(again.status).toBe(200);
+    expect(again.data.entries[0]?.status).toBe("duplicate");
+    expect(again.data.duplicates).toBe(1);
+
+    // The stored series is the first one, untouched — the no-op does not
+    // overwrite a curve the server already holds.
+    const afterSeries = await getPrismaClient().workoutSamples.findFirst({
+      where: { workout: { externalId: "hk-uuid-enrich-002" } },
+    });
+    expect(afterSeries).toEqual(storedSeries);
+    expect(
+      await getPrismaClient().workoutSamples.count({
+        where: { workout: { userId: TEST_USER_ID } },
+      }),
+    ).toBe(1);
+  });
+
+  it("hands the attach to exactly one of two concurrent enrichments", async () => {
+    await post({ workouts: [baseWorkout("hk-uuid-enrich-008")] });
+
+    // Both requests probe a workout with no series, so both mean to
+    // attach one. The unique index on `workout_id` decides: one write
+    // lands, the other conflicts and is skipped. The loser must report
+    // the duplicate it turned out to be rather than claim an attach the
+    // database never made — that is the arm this case exists for, and
+    // the outcome is deterministic even though the winner is not.
+    const { POST } = await import("@/app/api/workouts/batch/route");
+    const body = {
+      workouts: [baseWorkout("hk-uuid-enrich-008", { samples: SERIES })],
+    };
+    const [resA, resB] = await Promise.all([
+      POST(makeRequest(body)),
+      POST(makeRequest(body)),
+    ]);
+    expect(resA.status).toBe(200);
+    expect(resB.status).toBe(200);
+
+    const [jsonA, jsonB] = (await Promise.all([resA.json(), resB.json()])) as [
+      { data: BatchResponse },
+      { data: BatchResponse },
+    ];
+    const statuses = [
+      jsonA.data.entries[0]?.status,
+      jsonB.data.entries[0]?.status,
+    ].sort();
+    expect(statuses).toEqual(["duplicate", "enriched"]);
+    // Both responses still count the entry as a duplicate row.
+    expect(jsonA.data.duplicates).toBe(1);
+    expect(jsonB.data.duplicates).toBe(1);
+    expect(jsonA.data.inserted + jsonB.data.inserted).toBe(0);
+
+    const series = await getPrismaClient().workoutSamples.findMany({
+      where: { workout: { userId: TEST_USER_ID } },
+    });
+    expect(series).toHaveLength(1);
+    expect(series[0]?.sampleCount).toBe(3);
+    expect(
+      await getPrismaClient().workout.count({
+        where: { userId: TEST_USER_ID },
+      }),
+    ).toBe(1);
+  });
+
+  it("reports one enrichment when two entries in one batch aim at the same workout", async () => {
+    await post({ workouts: [baseWorkout("hk-uuid-enrich-007")] });
+
+    // Same external id twice, far enough apart in time that the
+    // write-time twin dedup keeps both entries. Only one series can land.
+    const res = await post({
+      workouts: [
+        baseWorkout("hk-uuid-enrich-007", { samples: SERIES }),
+        baseWorkout("hk-uuid-enrich-007", {
+          startedAt: "2026-05-14T09:00:00.000Z",
+          endedAt: "2026-05-14T09:45:00.000Z",
+          samples: [{ t: "2026-05-14T09:00:00.000Z", hr: 155 }],
+        }),
+      ],
+    });
+
+    expect(res.status).toBe(200);
+    expect(
+      res.data.entries.filter((e) => e.status === "enriched"),
+    ).toHaveLength(1);
+    expect(
+      await getPrismaClient().workoutSamples.count({
+        where: { workout: { userId: TEST_USER_ID } },
+      }),
+    ).toBe(1);
+  });
+
+  it("leaves every workout column byte-identical across an enrichment", async () => {
+    await post({
+      workouts: [
+        baseWorkout("hk-uuid-enrich-003", {
+          totalEnergyKcal: 388,
+          totalDistanceM: 7100,
+          avgHeartRate: 141,
+          maxHeartRate: 169,
+          minHeartRate: 96,
+          metadata: { device: "watch" },
+        }),
+      ],
+    });
+
+    const before = await getPrismaClient().workout.findFirstOrThrow({
+      where: { userId: TEST_USER_ID, externalId: "hk-uuid-enrich-003" },
+    });
+
+    // A re-post whose every field contradicts the stored row. First-write-
+    // wins still governs the workout itself; only the series is attached.
+    const enriched = await post({
+      workouts: [
+        baseWorkout("hk-uuid-enrich-003", {
+          sportType: "cycling",
+          startedAt: "2026-05-14T09:00:00.000Z",
+          endedAt: "2026-05-14T10:30:00.000Z",
+          totalEnergyKcal: 999,
+          totalDistanceM: 42000,
+          avgHeartRate: 111,
+          maxHeartRate: 198,
+          minHeartRate: 55,
+          metadata: { device: "phone" },
+          samples: SERIES,
+        }),
+      ],
+    });
+    expect(enriched.data.entries[0]?.status).toBe("enriched");
+
+    const after = await getPrismaClient().workout.findFirstOrThrow({
+      where: { userId: TEST_USER_ID, externalId: "hk-uuid-enrich-003" },
+    });
+    // Whole-row comparison — a spot check would miss a column nobody
+    // thought to name, and `updatedAt` proves no write touched the row.
+    expect(after).toEqual(before);
+  });
+
+  it("refuses a malformed samples array per entry without failing the batch", async () => {
+    await post({ workouts: [baseWorkout("hk-uuid-enrich-004")] });
+
+    const mixed = await post({
+      workouts: [
+        baseWorkout("hk-uuid-enrich-004", {
+          samples: [{ t: "not-a-timestamp", hr: 4000 }],
+        }),
+        baseWorkout("hk-uuid-enrich-005", {
+          startedAt: "2026-05-15T06:30:00.000Z",
+          endedAt: "2026-05-15T07:15:00.000Z",
+        }),
+      ],
+    });
+
+    expect(mixed.status).toBe(200);
+    expect(mixed.data.entries[0]?.status).toBe("skipped");
+    expect(mixed.data.entries[0]?.reason).toBe("invalid_samples");
+    expect(mixed.data.entries[1]?.status).toBe("inserted");
+    expect(mixed.data.inserted).toBe(1);
+    expect(mixed.data.skipped).toEqual([
+      { index: 0, reason: "invalid_samples" },
+    ]);
+
+    // Nothing attached to the workout the bad entry addressed.
+    expect(
+      await getPrismaClient().workoutSamples.count({
+        where: { workout: { userId: TEST_USER_ID } },
+      }),
+    ).toBe(0);
+    // And the second entry did land.
+    expect(
+      await getPrismaClient().workout.count({
+        where: { userId: TEST_USER_ID },
+      }),
+    ).toBe(2);
+  });
+
+  it("refuses an over-cap samples array per entry rather than the whole batch", async () => {
+    await post({ workouts: [baseWorkout("hk-uuid-enrich-006")] });
+
+    const oversized = Array.from({ length: 30_001 }, (_v, i) => ({
+      t: new Date(Date.UTC(2026, 4, 14, 6, 30, 0) + i * 1000).toISOString(),
+      hr: 120,
+    }));
+
+    const res = await post({
+      workouts: [baseWorkout("hk-uuid-enrich-006", { samples: oversized })],
+    });
+    expect(res.status).toBe(200);
+    expect(res.data.entries[0]?.status).toBe("skipped");
+    expect(res.data.entries[0]?.reason).toBe("invalid_samples");
+    expect(
+      await getPrismaClient().workoutSamples.count({
+        where: { workout: { userId: TEST_USER_ID } },
+      }),
+    ).toBe(0);
+  });
+
+  it("reports insert, enrich, duplicate and skip side by side in one batch", async () => {
+    await post({
+      workouts: [
+        baseWorkout("hk-uuid-mix-known-series", {
+          startedAt: "2026-05-10T06:00:00.000Z",
+          endedAt: "2026-05-10T06:45:00.000Z",
+        }),
+        baseWorkout("hk-uuid-mix-known-plain", {
+          startedAt: "2026-05-11T06:00:00.000Z",
+          endedAt: "2026-05-11T06:45:00.000Z",
+        }),
+      ],
+    });
+
+    const mixed = await post({
+      workouts: [
+        // 0 — new workout, inserts
+        baseWorkout("hk-uuid-mix-new", {
+          startedAt: "2026-05-12T06:00:00.000Z",
+          endedAt: "2026-05-12T06:45:00.000Z",
+        }),
+        // 1 — known workout with a series in the payload, enriches
+        baseWorkout("hk-uuid-mix-known-series", {
+          startedAt: "2026-05-10T06:00:00.000Z",
+          endedAt: "2026-05-10T06:45:00.000Z",
+          samples: SERIES,
+        }),
+        // 2 — known workout, no series in the payload, unchanged
+        baseWorkout("hk-uuid-mix-known-plain", {
+          startedAt: "2026-05-11T06:00:00.000Z",
+          endedAt: "2026-05-11T06:45:00.000Z",
+        }),
+        // 3 — unusable external id, refused per entry
+        baseWorkout("   ", {
+          startedAt: "2026-05-13T06:00:00.000Z",
+          endedAt: "2026-05-13T06:45:00.000Z",
+        }),
+      ],
+    });
+
+    expect(mixed.status).toBe(200);
+    expect(mixed.data.processed).toBe(4);
+    expect(mixed.data.entries.map((e) => e.status)).toEqual([
+      "inserted",
+      "enriched",
+      "duplicate",
+      "skipped",
+    ]);
+    expect(mixed.data.inserted).toBe(1);
+    // An enriched entry is still a duplicate of the workout row itself —
+    // the counters keep counting rows, the entry status carries the detail.
+    expect(mixed.data.duplicates).toBe(2);
+    expect(mixed.data.skipped).toHaveLength(1);
+
+    const series = await getPrismaClient().workoutSamples.findMany({
+      where: { workout: { userId: TEST_USER_ID } },
+      include: { workout: { select: { externalId: true } } },
+    });
+    expect(series).toHaveLength(1);
+    expect(series[0]?.workout.externalId).toBe("hk-uuid-mix-known-series");
+    expect(
+      await getPrismaClient().workout.count({
+        where: { userId: TEST_USER_ID },
+      }),
+    ).toBe(3);
+  });
+});