Problem Statement

Currently, the update_pull_request tool doesn't support updating labels on existing pull requests in Azure DevOps. While we recently added label support to create_pull_request, users cannot modify labels after a PR has been created through the MCP tools.

Proposed Solution

Add an optional labels parameter to the update_pull_request tool that accepts an array of label names. The behavior should follow the same pattern as other optional update fields:

• undefined (not provided): Don't modify existing labels
• [] (empty array): Remove all labels from the PR
• ["label1", "label2"]: Replace existing labels with the specified ones

Implementation Approach

Similar to the create_pull_request implementation:

1. Add an optional labels parameter to the update_pull_request tool schema (array of strings, optional)
2. Map the label names to WebApiTagDefinition[] format when provided: labels.map((label) => ({ name: label }))
3. Only include labels in the update request if the parameter is defined:

   if (labels !== undefined) {
     updateRequest.labels = labels.map((label) => ({ name: label }));
   }

4. Add comprehensive tests to verify:
   • Labels are not updated when parameter is undefined
   • All labels are removed when empty array is provided
   • Labels are replaced when array with values is provided

Benefits

• Completes the label management story for pull requests
• Consistent API pattern with other update fields (title, description, etc.)
• Single API call to update labels instead of separate operations
• Allows removing all labels by passing empty array