fix(tasks): avoid dropping completed task results during collection

[coinmoles]

Remove the std::mem::take from OperationProcessor::collect_completed_results

Motivation and Context

std::mem::take would clear OperationProcessor::completed_results, causing completed tasks to be dropped. This made tasks/get and tasks/result to fail for subsequent requests.

How Has This Been Tested?

• All existing tests passed
• Tested with a custom task server/client implementation (Will add this to examples if requested)

Breaking Changes

This is technically a breaking change that changes the return type of OperationProcessor::collect_completed_results from Vec<TaskResult> to (). However, I doubt there was anyone calling the method directly without using the #[tool_handler] macro.

I did this to avoid introducing an unnecessary clone call. If this is a problem, I can change the method so it returns either:

• self.completed_results.clone()
• An owned vector of newly collected items, which I think was the intended return value in the first place.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

Fixes #638

[alexhancock]

thoughts on this being pub in the first place?

[coinmoles]

Right now, the function has to be public because it is called from the output of #[task_handler] macro.

However, it would make sense to make this private and have OperationProcessor::peek_completed and OperationProcessor::take_completed_result call this before returning. Do you think that would be better?

[alexhancock]

Yes, something like that makes sense to me. Can you make the change?