Return the branch web_url from the add_branch MCP tool

What does this MR do and why?

add_branch is the MCP counterpart of POST /projects/:id/repository/branches, which returns web_url for the created branch, and it is aliased as create_branch. Its GraphQL-backed implementation returns only what Types::BranchType exposes — name and commit — because the Gitlab::Git::Branch behind that type carries no project to build a URL from. This MR restores parity with the REST endpoint by adding the URL in the tool's process_result, where the project is already resolved, the same way get_job uses project_job_url.

This MR adds the URL back in the tool's process_result, where the project has already been resolved, using project_tree_url as get_job does with project_job_url. The GraphQL type is unchanged, so no schema or docs change is needed. Both the text content and structuredContent carry the field.

References

• Resolves #611539 (closed)
• Related: !248453 (merged)

Differences

Before: The add_branch tool response contains branch: { name, commit }.

After: The response contains branch: { name, commit, web_url }, where web_url points at the branch's tree page.

How to set up and validate locally

1. Call the tool through the MCP endpoint:

   curl -s -X POST "http://gdk.test:3000/api/v4/mcp" \
     -H "Authorization: Bearer <mcp-scoped token>" -H "Content-Type: application/json" \
     -d '{"jsonrpc":"2.0","id":"1","method":"tools/call","params":{"name":"add_branch","arguments":{"project_id":"<full path>","branch":"mcp-test","ref":"master"}}}'

2. result.structuredContent.branch.web_url is present and resolves to the new branch.

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