fix: revert zod import change (#9382)

## Background

Changing `import { z } from 'zod/v4';` to `import * as z from 'zod/v4';`
broke AI SDK zod schemas in some environments.

## Summary

Revert import change.

## Related

- Caused by #9301
- port of #9349

---------

Co-authored-by: Lars Grammel <[email protected]>

Author: gr2m

.changeset/young-beans-melt.md

@@ -1,6 +1,6 @@
 import { expectTypeOf } from 'vitest';
 import { generateObject } from './generate-object';
-import * as z from 'zod/v4';
+import { z } from 'zod/v4';
 import { JSONValue } from '@ai-sdk/provider';
 import { describe, it } from 'vitest';
 

packages/ai/src/generate-object/generate-object.test-d.ts

@@ -15,7 +15,7 @@ import {
   vitest,
   vi,
 } from 'vitest';
-import * as z from 'zod/v4';
+import { z } from 'zod/v4';
 import { verifyNoObjectGeneratedError as originalVerifyNoObjectGeneratedError } from '../error/verify-no-object-generated-error';
 import * as logWarningsModule from '../logger/log-warnings';
 import { MockLanguageModelV3 } from '../test/mock-language-model-v3';

packages/ai/src/generate-object/generate-object.test.ts

@@ -1,6 +1,6 @@
 import { JSONValue } from '@ai-sdk/provider';
 import { expectTypeOf } from 'vitest';
-import * as z from 'zod/v4';
+import { z } from 'zod/v4';
 import { AsyncIterableStream } from '../util/async-iterable-stream';
 import { FinishReason } from '../types';
 import { streamObject } from './stream-object';

packages/ai/src/generate-object/stream-object.test-d.ts

@@ -12,7 +12,7 @@ import {
 } from '@ai-sdk/provider-utils/test';
 import assert, { fail } from 'node:assert';
 import { afterEach, beforeEach, describe, expect, it, vitest } from 'vitest';
-import * as z from 'zod/v4';
+import { z } from 'zod/v4';
 import { NoObjectGeneratedError } from '../error/no-object-generated-error';
 import { verifyNoObjectGeneratedError } from '../error/verify-no-object-generated-error';
 import * as logWarningsModule from '../logger/log-warnings';

packages/ai/src/generate-object/stream-object.test.ts

@@ -25,7 +25,7 @@ import {
   vi,
   vitest,
 } from 'vitest';
-import * as z from 'zod/v4';
+import { z } from 'zod/v4';
 import { Output } from '.';
 import * as logWarningsModule from '../logger/log-warnings';
 import { MockLanguageModelV3 } from '../test/mock-language-model-v3';

packages/ai/src/generate-text/generate-text.test.ts

@@ -1,5 +1,5 @@
 import { fail } from 'assert';
-import * as z from 'zod/v4';
+import { z } from 'zod/v4';
 import { verifyNoObjectGeneratedError } from '../error/verify-no-object-generated-error';
 import { object } from './output';
 import { FinishReason } from '../types';

packages/ai/src/generate-text/output.test.ts

@@ -1,5 +1,5 @@
 import { dynamicTool, tool } from '@ai-sdk/provider-utils';
-import * as z from 'zod/v4';
+import { z } from 'zod/v4';
 import { InvalidToolInputError } from '../error/invalid-tool-input-error';
 import { NoSuchToolError } from '../error/no-such-tool-error';
 import { ToolCallRepairError } from '../error/tool-call-repair-error';

packages/ai/src/generate-text/parse-tool-call.test.ts

@@ -6,7 +6,7 @@ import {
   mockId,
 } from '@ai-sdk/provider-utils/test';
 import { describe, expect, it } from 'vitest';
-import * as z from 'zod/v4';
+import { z } from 'zod/v4';
 import { NoSuchToolError } from '../error/no-such-tool-error';
 import { MockTracer } from '../test/mock-tracer';
 import { runToolsTransformation } from './run-tools-transformation';

packages/ai/src/generate-text/run-tools-transformation.test.ts

@@ -35,7 +35,7 @@ import {
   vi,
   vitest,
 } from 'vitest';
-import * as z from 'zod/v4';
+import { z } from 'zod/v4';
 import * as logWarningsModule from '../logger/log-warnings';
 import { MockLanguageModelV3 } from '../test/mock-language-model-v3';
 import { createMockServerResponse } from '../test/mock-server-response';