fix(ai): preserve tool approval signature when transitioning to appro…

[luluwux]

Background

When experimental_toolApprovalSecret is configured, resuming after a tool approval fails with AI_InvalidToolApprovalSignatureError: missing signature.

This happens because the client-side state manager drops approval.signature when transitioning from the approval-requested state to the approval-responded state in two places:

1. In AbstractChat.addToolApprovalResponse (manual approval) — rebuilt approval as { id, approved, reason } without carrying forward signature.
2. In processUIMessageStream under the tool-approval-response case (streamed/automatic) — rebuilt toolInvocation.approval carrying isAutomatic but omitting signature.

Consequently, convertToModelMessages later read part.approval.signature as undefined, causing the server-side verification check to throw.

Summary

• packages/ai/src/ui/chat.ts:
  • Updated addToolApprovalResponse to preserve part.approval.signature when mapping and updating message parts.
• packages/ai/src/ui/process-ui-message-stream.ts:
  • Updated the tool-approval-response case to carry forward the previous approval.signature into the updated toolInvocation.approval object.
• packages/ai/src/ui/chat.test.ts:
  • Added approved with signature unit test to verify signature preservation for manual approvals.
• packages/ai/src/ui/process-ui-message-stream.test.ts:
  • Added automatic tool approval signature preservation unit test to verify signature preservation for streamed/automatic approvals.

Manual Verification

• Verified the state transitions and signature preservation via the newly added automated unit tests. All tests run successfully:

  ✓ src/ui/chat.test.ts (30 tests) 662ms
  ✓ src/ui/process-ui-message-stream.test.ts (115 tests) 1.59s
  
  

Checklist

• Tests have been added / updated (for bug fixes / features)
• A patch changeset for relevant packages has been added (for bug fixes / features)
• I have reviewed this pull request (self-review)

Note

Please make sure to sign your commits as required by the repository guidelines before merging.

Related Issues

Fixes #16543