feat: ALTK JSON Processing native plugin

[jsntsay]

Summary

LLMs tend to be very poor at parsing long or complex JSON objects. This plugin uses the JSON Processor component from the Agent Lifecycle Toolkit to detect long JSON responses and then parses long responses using a given query.

Notes

This PR adds the ALTKJsonProcessor plugin as a native plugin. An optional dependency to the agent-lifecycle-toolkit package in pypi is added as a optional dependency group. There is a dev dependency conflict with pyre-check due to its hard dataclasses-json==0.5.7 dependency.

[terylt]

Is each section of the providers required? or optional?

[jsntsay]

Optional, I can mark it as such.

[terylt]

We may not want to add this into the config.yaml by default as it will require the optional requirement of altk to be always need to be added.

[jsntsay]

Even if the plugin is disabled? What would be the right thing to do then? Separate config.yaml in the plugin directory?

[terylt]

what are the implications of removing pyre-check when altk isn't installed? Do all the tests pass?

[jsntsay]

I think it's supposed to be used in linting but as far as I can tell the current linter list doesn't use it:

mcp-context-forge/Makefile

Line 841 in fa92384

LINTERS := isort flake8 pylint mypy bandit pydocstyle pycodestyle pre-commit \

(I'm assuming pyrefly is replacing it)

[crivetimihai]

Must Fix

• Add error messages (lines 80-100 just throw bare exceptions)
• Fix README (remove .env stuff, add query examples)
• Add basic tests
• Fix manifest: tool_post_hook → tool_post_invoke
• Check length before parsing JSON (perf)

Should Fix

• Validate empty jsonprocessor_query
• Explain why pyre-check was removed
• Warn about LLM API costs

[jsntsay]

Addressed feedback in the following ways:

• More descriptive error messages added for the provider initialization section
• README more descriptive, with the .env stuff removed, more descriptions of how to configure the LLM provider, example queries, discussion of LLM costs, and testing.
• Added unit test in tests/unit/mcp_gateway/plugins/plugins/altk_json_processor
• Fixed manifest
• Now checking length before checking if response is JSON
• Made clear in config that LLM provider sections are optional
• Validates empty jsonprocessor_query via providing an empty string default

Explain why pyre-check was removed:
pyre-check does not seem to actually be used in any of the linting (see Makefile) and conflicts with the agent-lifecycle-toolkit library due to its hard dataclasses-json==0.5.7 dependency. pyre-check also has been superseded by pyrefly which is what is currently being used during linting. I didn't add it back as an optional dependency because uv complains since it checks all options. I can add the optional dependency if necessary though.