Bug: get_pull_request_diff Fails Schema Validation Due to Raw String Output

When calling the get_pull_request_diff tool, the operation fails with the error: MCP error -32600: Structured content does not match the tool's output schema: data should NOT have additional properties.

Root Cause

An investigation revealed a mismatch between the PullRequestService.getPullRequestDiff implementation and the expectations of the generic toolService.

1. OpenAPI Definition: The openapi.yaml correctly defines the response for this endpoint as text/plain.
2. Tool Service Behavior: The generic toolService.mjs, when it encounters a text/plain response type, wraps the output schema in a JSON object for client compatibility. It expects the tool's handler to return a JSON object of the shape { "result": "..." }.
3. Service Implementation: The PullRequestService.getPullRequestDiff method currently returns the raw string output (stdout) from the gh pr diff command, not a JSON object.

This discrepancy causes the tool's output validation to fail.

Resolution

The getPullRequestDiff method in ai/mcp/server/github-workflow/services/PullRequestService.mjs needs to be modified. Instead of returning the raw stdout string, it must return a JSON object that conforms to the structure expected by the tool service:

// Current incorrect return value
return stdout;

// Required correct return value
return { result: stdout };

This will align the service's output with the tool's schema, resolving the validation error.