feature: Tool response processing with nemo check

[evaline-ju]

Feature Description

In #17 a plugin was added to interface with the "nemo check server" (server that provides /v1/guardrails/checks). This focused on tool argument checking (pre-tool-execution). We want to leverage the capability of checking tool responses as well.

Proposed Solution

Unless the hook mechanism has changed

• Update tool_post_invoke "hook" in the NemoCheck plugin to call out to /v1/guardrails/checks with the appropriate role: tool and tool response content
• Update the getToolPostInvokeResponse as needed in the main ext-proc server to make sure that error response information is propagated and blocking requests (continue_processing: false) leads to an expected MCP error

Want to contribute?

• I would like to work on this issue.

Additional Context

No response

[julianstephen]

The logic in tool_pre_invoke and tool_post_invoke seems pretty similar unless we want to config pre_invoke specific vs post_invoke specific check guard. I can take a shot at refactoring the pre_invoke calls so that post_invoke can simply make the same call.

[evaline-ju]

@julianstephen I think based on the current hooks we'll end up making slightly different Nemo check calls. WIP on this branch: https://github.com/evaline-ju/plugins-adapter/tree/tool-response but there's definitely common code we can try to refactor