List unknown and accepted parameter names in MCP validation errors

Pavan Kumar Sadashivrequested to merge
gitlab-community/gitlab-org/gitlab:hrlpavan-635931-mcp-validation-error-unknown-params into master

What does this merge request do and why?

When Mcp::Tools::Base::BaseService#validate_arguments! rejects an undeclared top-level parameter via additionalProperties: false:

  1. Report the parameter as Unknown parameter '<field>'. Accepted parameters: <properties> instead of <field> is invalid, so agents can immediately see the valid parameter names without guessing or re-reading the schema.
  2. Report all missing required keys (error['details']['missing_keys']) instead of only .first.

References

Closes #635931

How to set up and validate locally

  1. Run the base service and tool call specs: 
    bundle exec rspec spec/services/mcp/tools/base/base_service_spec.rb spec/requests/api/mcp/handlers/call_tool_spec.rb

Merge request reports