diff --git a/my-tools/authorize_next_wbv2_task.py b/my-tools/authorize_next_wbv2_task.py
index ebe52cdf1..ce7a2c4ad 100644
--- a/my-tools/authorize_next_wbv2_task.py
+++ b/my-tools/authorize_next_wbv2_task.py
@@ -440,6 +440,7 @@ PREFERRED_BATCHES = [
 # command gate and fixture; no recipe is allowed to infer coverage from a
 # source filename alone.
 AUTO_OPERATOR_RECIPES = [
+    {"moduleId": "OBJECT_MATERIAL_SLOT_ASSIGN_OPERATOR_BATCH", "title": "verify material slot assign operator through native Main", "owner": "OBJECT", "identifier": "OBJECT_OT_material_slot_assign", "fixture": "tests/files/web/basic_scene.blend", "test": "web/tests/e2e/wbv2-material-slot-assign-batch-production.spec.ts", "production": "tests/golden/{task}/material-slot-assign-production.json", "operation": "MATERIAL_SLOT_ASSIGN"},
     {"moduleId": "OBJECT_MATERIAL_SLOT_REMOVE_OPERATOR_BATCH", "title": "verify material slot remove operator through native Main", "owner": "OBJECT", "identifier": "OBJECT_OT_material_slot_remove", "fixture": "tests/files/web/basic_scene.blend", "test": "web/tests/e2e/wbv2-material-slot-production.spec.ts", "production": "tests/golden/{task}/material-slot-production.json", "operation": "MATERIAL_SLOT_REMOVE", "slotOperation": "REMOVE"},
     {"moduleId": "MESH_DECIMATE_OPERATOR_BATCH", "title": "verify mesh decimate operator through native Main", "owner": "MESH", "identifier": "MESH_OT_decimate", "fixture": "tests/files/web/generated/WBV2-P4-001-MODIFIER.DECLARED_SLICES.blend", "test": "web/tests/e2e/wbv2-modifier-parameter-production.spec.ts", "production": "tests/golden/{task}/modifier-parameter-production.json", "operation": "DECIMATE"},
     {"moduleId": "OBJECT_MATERIAL_SLOT_ADD_OPERATOR_BATCH", "title": "verify material slot add operator through native Main", "owner": "OBJECT", "identifier": "OBJECT_OT_material_slot_add", "fixture": "tests/files/web/basic_scene.blend", "test": "web/tests/e2e/wbv2-material-slot-production.spec.ts", "production": "tests/golden/{task}/material-slot-production.json", "operation": "MATERIAL_SLOT_ADD"},
diff --git a/web/tests/e2e/wbv2-material-slot-assign-batch-production.spec.ts b/web/tests/e2e/wbv2-material-slot-assign-batch-production.spec.ts
new file mode 100644
index 000000000..8d35a044d
--- /dev/null
+++ b/web/tests/e2e/wbv2-material-slot-assign-batch-production.spec.ts
@@ -0,0 +1,52 @@
+import crypto from "node:crypto";
+import fs from "node:fs";
+import path from "node:path";
+import { expect, test } from "@playwright/test";
+
+const root = path.resolve(import.meta.dirname, "../../..");
+const fixturePath = process.env.WBV2_BATCH_FIXTURE ?? "tests/files/web/basic_scene.blend";
+const fixture = fs.readFileSync(path.join(root, fixturePath));
+const fixtureSha256 = crypto.createHash("sha256").update(fixture).digest("hex");
+const task = process.env.WBV2_BATCH_TASK ?? "WBV2-MATERIAL-SLOT-ASSIGN";
+const productionPath = process.env.WBV2_BATCH_PRODUCTION ?? `tests/golden/${task}/material-slot-assign-production.json`;
+const sourceUnits = JSON.parse(process.env.WBV2_BATCH_UNITS ?? "[\"operator:OBJECT_OT_material_slot_assign\"]") as string[];
+
+test("native material slot assign batch preserves Main recovery semantics", async ({ page }) => {
+  await page.goto("/");
+  const result = await page.evaluate(async (bytes) => {
+    const { WebEngineClient } = await import("/src/engine-client/WebEngineClient.ts");
+    const client = new WebEngineClient({ timeoutMs: 60_000 });
+    const reopened = new WebEngineClient({ timeoutMs: 60_000 });
+    const shape = (error: any) => ({ code: error?.code, message: error?.message });
+    try {
+      const opened = await client.openBlend(Uint8Array.from(bytes).buffer);
+      const object: any = opened.snapshot.nodes.find((node: any) => node.type === "MESH");
+      const mesh: any = object && opened.snapshot.meshes.find((candidate: any) => candidate.id === object.dataId);
+      if (!object || !mesh || !mesh.faceCount) throw new Error("basic scene has no mesh face");
+      const added = await client.applyCommand({ type: "addMaterialSlot", objectId: object.id, name: "WebAssignMaterial" } as any);
+      const slotIndex = (added.snapshot.nodes.find((node: any) => node.id === object.id)?.materialSlotIds?.length ?? 1) - 1;
+      const assigned = await client.applyCommand({ type: "assignMaterialFaces", meshId: mesh.id, faceIndices: [0], slotIndex } as any);
+      const undo = await client.applyCommand({ type: "undo" });
+      const redo = await client.applyCommand({ type: "redo" });
+      const malformed = await client.applyCommand({ type: "assignMaterialFaces", meshId: "mesh:missing", faceIndices: [0], slotIndex } as any).then(() => ({ code: "NO_ERROR" })).catch(shape);
+      const afterMalformed = await client.snapshot();
+      const saved = await client.saveBlend();
+      const restored = await reopened.openBlend(saved.slice(0));
+      const assignedMesh: any = assigned.snapshot.meshes.find((candidate: any) => candidate.id === mesh.id);
+      const restoredMesh: any = restored.snapshot.meshes.find((candidate: any) => candidate.id === mesh.id);
+      return { browser: "chromium", baseRevision: opened.snapshot.revision, addRevision: added.snapshot.revision, assignRevision: assigned.snapshot.revision, undoRevision: undo.snapshot.revision, redoRevision: redo.snapshot.revision, assigned: Boolean(assignedMesh?.materialSlotIds?.length && assignedMesh.materialSlotIds.includes("material:WebAssignMaterial")), restored: Boolean(restoredMesh?.materialSlotIds?.length && restoredMesh.materialSlotIds.includes("material:WebAssignMaterial")), assignedMesh, restoredMesh, malformed, malformedRevisionPreserved: afterMalformed.snapshot.revision === redo.snapshot.revision, reopenedRevision: restored.snapshot.revision };
+    } finally { client.terminate(); reopened.terminate(); }
+  }, Array.from(fixture));
+  fs.mkdirSync(path.dirname(path.join(root, productionPath)), { recursive: true });
+  fs.writeFileSync(path.join(root, productionPath), `${JSON.stringify({ schemaVersion: 1, task, operation: "MATERIAL_SLOT_ASSIGN_ENGINE_CHROMIUM", browser: "chromium", queueMutation: false, fixture: fixturePath, fixtureSha256, sourceUnits, ...result }, null, 2)}\n`);
+  expect(result.browser).toBe("chromium");
+  expect(result.addRevision).toBe(result.baseRevision + 1);
+  expect(result.assignRevision).toBe(result.baseRevision + 2);
+  expect(result.undoRevision).toBe(result.baseRevision + 3);
+  expect(result.redoRevision).toBe(result.baseRevision + 4);
+  expect(result.assigned).toBe(true);
+  expect(result.restored).toBe(true);
+  expect(result.malformed.code).not.toBe("NO_ERROR");
+  expect(result.malformedRevisionPreserved).toBe(true);
+  expect(result.reopenedRevision).toBe(1);
+});