fix(data-plane): accept exact replacement replays

services/external-data-plane/test/data-product-delivery.integration.test.mjs

@@ -232,6 +232,26 @@ try {
   );
   assert.equal(firstZoneGeneration.currentUpdatedCount, 2);
   assert.equal(firstZoneGeneration.currentRemovedCount, 0);
+  const replayedFirstZoneGeneration = await persistDataProductPublish(
+    pool,
+    zoneBatch("zones-01-stable-replay-key", firstZoneGenerationAt, [
+      zoneFact("zone-01", firstZoneGenerationAt),
+      zoneFact("zone-02", firstZoneGenerationAt),
+    ]),
+    storedZoneDefinition,
+  );
+  assert.equal(replayedFirstZoneGeneration.idempotent, true);
+  assert.equal(replayedFirstZoneGeneration.publishedFactCount, 2);
+  assert.equal(replayedFirstZoneGeneration.currentUpdatedCount, 0);
+  assert.equal(replayedFirstZoneGeneration.currentRemovedCount, 0);
+  assert.equal(replayedFirstZoneGeneration.patchOperationCount, 0);
+  assert.equal(replayedFirstZoneGeneration.cursor, firstZoneGeneration.cursor);
+  await assert.rejects(
+    persistDataProductPublish(pool, zoneBatch("zones-01-conflicting-replay", firstZoneGenerationAt, [
+      zoneFact("zone-01", firstZoneGenerationAt),
+    ]), storedZoneDefinition),
+    (error) => error?.status === 409 && error?.code === "data_product_generation_not_newer",
+  );
   const secondZoneGenerationAt = "2026-07-15T10:11:00.000Z";
   const secondZoneGeneration = await persistDataProductPublish(
     pool,

services/external-data-plane/test/data-product-delivery.test.mjs

@@ -1,6 +1,9 @@
 import assert from "node:assert/strict";
 
-import { assertPublishMatchesDefinition } from "../src/data-product-delivery.mjs";
+import {
+  assertPublishMatchesDefinition,
+  classifyReplacementGeneration,
+} from "../src/data-product-delivery.mjs";
 import { normalizeDataProductDefinition } from "../src/data-product-policy.mjs";
 
 const definition = normalizeDataProductDefinition({
@@ -92,4 +95,42 @@ assert.doesNotThrow(() => assertPublishMatchesDefinition({
   }],
 }, legacyDefinition));
 
+const acceptedGeneration = "2026-07-15T10:10:00.000Z";
+assert.equal(classifyReplacementGeneration({
+  currentGenerationAt: null,
+  generationAt: acceptedGeneration,
+}), "advance");
+assert.equal(classifyReplacementGeneration({
+  currentGenerationAt: acceptedGeneration,
+  generationAt: "2026-07-15T10:11:00.000Z",
+}), "advance");
+assert.equal(classifyReplacementGeneration({
+  currentGenerationAt: acceptedGeneration,
+  generationAt: acceptedGeneration,
+  incomingCount: 903,
+  currentCount: 903,
+  matchingCount: 903,
+}), "replay");
+assert.equal(classifyReplacementGeneration({
+  currentGenerationAt: acceptedGeneration,
+  generationAt: acceptedGeneration,
+  incomingCount: 903,
+  currentCount: 903,
+  matchingCount: 902,
+}), "conflict");
+assert.equal(classifyReplacementGeneration({
+  currentGenerationAt: acceptedGeneration,
+  generationAt: acceptedGeneration,
+  incomingCount: 902,
+  currentCount: 903,
+  matchingCount: 902,
+}), "conflict");
+assert.equal(classifyReplacementGeneration({
+  currentGenerationAt: acceptedGeneration,
+  generationAt: "2026-07-15T10:09:00.000Z",
+  incomingCount: 903,
+  currentCount: 903,
+  matchingCount: 903,
+}), "stale");
+
 console.log("external-data-plane data product delivery policy: ok");