fix(mastra): vendor sync partial-JSON parser, drop @ai-sdk/ui-utils

integrations/mastra/typescript/package.json

@@ -57,10 +57,9 @@
   },
   "dependencies": {
     "@ag-ui/a2ui-toolkit": "workspace:*",
-    "@ai-sdk/ui-utils": "^1.1.19",
     "fast-json-patch": "^3.1.1",
     "rxjs": "7.8.1",
-    "zod": "^3.25.76"
+    "zod": "^3.25.76 || ^4.0.0"
   },
   "peerDependencies": {
     "@ag-ui/core": ">=1.0.0",

integrations/mastra/typescript/src/mastra.ts

@@ -35,7 +35,11 @@ import type { Agent as LocalMastraAgent } from "@mastra/core/agent";
 import { RequestContext } from "@mastra/core/request-context";
 import { randomUUID } from "@ag-ui/client";
 import jsonpatch from "fast-json-patch";
-import { parsePartialJson } from "@ai-sdk/ui-utils";
+// Vendored synchronous copy of @ai-sdk/ui-utils' parsePartialJson, as Mastra did in
+// https://github.com/mastra-ai/mastra/pull/27297. Fixes
+// https://github.com/ag-ui-protocol/ag-ui/issues/3096 and
+// https://github.com/ag-ui-protocol/ag-ui/issues/2874.
+import { parsePartialJson } from "./utils/ai-sdk-v4";
 import { Observable, type Subscriber } from "rxjs";
 import { MastraClient } from "@mastra/client-js";
 import {

integrations/mastra/typescript/src/utils/ai-sdk-v4/ai-sdk-v4.test.ts

@@ -0,0 +1,57 @@
+import { parsePartialJson } from ".";
+import { fixJson } from "./fix-json";
+
+// The vendored parser replaces @ai-sdk/ui-utils' parsePartialJson (#3096, #2874),
+// following Mastra's copy in https://github.com/mastra-ai/mastra/pull/27297.
+// The first case is Mastra's own test; the rest pin the shapes the working-memory
+// streaming bridge in mastra.ts feeds it.
+
+describe("parsePartialJson (vendored)", () => {
+  it("reports each parse state (Mastra's test case)", () => {
+    expect(parsePartialJson(undefined)).toEqual({
+      value: undefined,
+      state: "undefined-input",
+    });
+    expect(parsePartialJson('{"a":1}')).toEqual({
+      value: { a: 1 },
+      state: "successful-parse",
+    });
+    expect(parsePartialJson('{"a":[1,"tw')).toEqual({
+      value: { a: [1, "tw"] },
+      state: "repaired-parse",
+    });
+    expect(parsePartialJson("}{")).toEqual({
+      value: undefined,
+      state: "failed-parse",
+    });
+  });
+
+  it("is synchronous", () => {
+    expect(parsePartialJson('{"a":1}')).not.toBeInstanceOf(Promise);
+  });
+
+  it("repairs the streamed working-memory envelope and its nested JSON string", () => {
+    const outer = parsePartialJson(
+      '{"memory":"{\\"recipe\\":{\\"title\\":\\"Sp',
+    );
+    expect(outer.state).toBe("repaired-parse");
+    const memory = (outer.value as { memory: string }).memory;
+    expect(parsePartialJson(memory).value).toEqual({
+      recipe: { title: "Sp" },
+    });
+  });
+
+  it("repairs dangling keys, literals and numbers", () => {
+    expect(parsePartialJson('{"memory":').value).toEqual({});
+    expect(parsePartialJson('{"done":tr').value).toEqual({ done: true });
+    expect(parsePartialJson('{"a":1,"b":').value).toEqual({ a: 1 });
+  });
+});
+
+describe("fixJson (vendored)", () => {
+  it("closes open strings, arrays and objects", () => {
+    expect(JSON.parse(fixJson('{"a":"he'))).toEqual({ a: "he" });
+    expect(JSON.parse(fixJson('{"a":['))).toEqual({ a: [] });
+    expect(JSON.parse(fixJson('{"a":"x\\"y'))).toEqual({ a: 'x"y' });
+  });
+});