[mcp] fix: reject null RPC params

[Wangmerlyn]

Summary

• Reject explicit JSON-RPC params:null and other non-object params before method dispatch.
• Preserve omitted params as legacy empty-object direct calls.
• Add regression coverage proving stop_keep params:null does not stop existing sessions.
• Update AGENTS and MCP/CLI docs for the parameter contract.

Test Plan

• RED: PYTHONPATH=src pytest 'tests/mcp/test_server.py::test_jsonrpc_stop_keep_rejects_null_params_without_stopping_sessions' -q failed before the fix because active-job was stopped.
• PYTHONPATH=src pytest 'tests/mcp/test_server.py::test_jsonrpc_stop_keep_rejects_null_params_without_stopping_sessions' -q
• PYTHONPATH=src pytest tests/mcp/test_server.py -q
• mkdocs build --strict
• pre-commit run --all-files --show-diff-on-failure
• PYTHONPATH=src pytest tests -q

Local Review

• Local subagent code review: no Critical, Important, or Minor issues; ready to merge.

Summary by CodeRabbit

• Bug Fixes
  • Clarified JSON-RPC handling so omitted params are treated as an empty object for compatibility, while params: null or other non-object values are rejected with Invalid params.
  • Prevented invalid direct calls from triggering any method side effects before validation completes.
• Documentation
  • Updated user-facing JSON-RPC and CLI guidance to reflect the expected behavior for omitted and invalid params values.
• Tests
  • Added coverage to verify invalid params are rejected and the active session remains unchanged.

[gemini-code-assist]

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: de40df81-daa9-4d32-a4ad-b2a719b7e2f6

📥 Commits

Reviewing files that changed from the base of the PR and between e467e5f and 7425f5a.

📒 Files selected for processing (5)

• AGENTS.md
• docs/guides/mcp.md
• docs/reference/cli.md
• src/keep_gpu/mcp/server.py
• tests/mcp/test_server.py

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📝 Walkthrough

Walkthrough

The server's JSON-RPC request handler now explicitly checks for the presence of the params key rather than using a default-get pattern, preserving the existing rejection of non-dictionary params. A new test validates that null params are rejected without side effects. Documentation is updated to reflect this validation behavior.

Changes

JSON-RPC params validation

Layer / File(s)	Summary
Server params extraction and validation src/keep_gpu/mcp/server.py	_handle_request uses an explicit "params" in payload check instead of payload.get, defaulting to {} only when absent, and continues to raise JSONRPC_INVALID_PARAMS for non-dict params.
Regression test for null params tests/mcp/test_server.py	New test confirms stop_keep with params=None returns INVALID_PARAMS and leaves the active session and its controller unaffected.
Documentation updates AGENTS.md, docs/guides/mcp.md, docs/reference/cli.md	Docs clarify that omitted params default to an empty object while params: null or non-object params triggers -32602 Invalid params before any method side effects.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Possibly related PRs

• Wangmerlyn/KeepGPU#86: Both PRs modify JSON-RPC params handling and validation logic in src/keep_gpu/mcp/server.py, resulting in aligned -32602 Invalid params behavior.

Poem

A rabbit checks each params with care,
Is it null, or nothing there?
Empty dict for the missing kind,
But null gets firmly left behind.
No side effects, no stopping spree—
Just -32602, plain to see. 🐇

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main change: rejecting null RPC params in MCP JSON-RPC handling.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch codex/mcp-reject-null-params

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