fix: handle nil Params in ParseToolArguments

[lpcox]

Problem

CallToolRequest is ServerRequest[*CallToolParamsRaw] — Params is a pointer type that defaults to nil when not explicitly initialized. ParseToolArguments accessed req.Params.Arguments without checking for nil, causing a nil pointer dereference panic.

Fix

• Added nil check for req.Params in ParseToolArguments() before accessing req.Params.Arguments
• Fixed test cases to properly initialize Params via struct literals instead of assigning to a nil pointer field
• Added a dedicated nil params returns empty map test case

Testing

All tests pass (make agent-finished ✅).

[Copilot]

Pull request overview

This PR fixes a nil-pointer panic in MCP tool argument parsing by safely handling CallToolRequest.Params being nil, and updates/adds tests to reflect correct request construction.

Changes:

• Guarded ParseToolArguments() against req.Params == nil before accessing Arguments.
• Updated tests to initialize CallToolRequest.Params via struct literals instead of mutating a nil pointer field.
• Added a dedicated test case for “nil params returns empty map”.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
internal/mcp/tool_result.go	Adds a nil check for req.Params in ParseToolArguments to prevent panics.
internal/mcp/tool_result_test.go	Adjusts request construction in tests and adds coverage for nil Params.

Comments suppressed due to low confidence (1)

internal/mcp/tool_result.go:117

• ParseToolArguments can still return a nil map when Arguments is present but set to JSON null (json.Unmarshal succeeds and leaves toolArgs nil). This is inconsistent with the “no arguments → empty map” behavior and with callers that may assume a non-nil args object; consider normalizing toolArgs to an empty map after unmarshal when it’s nil (and ideally add a test for arguments: null).

func ParseToolArguments(req *sdk.CallToolRequest) (map[string]interface{}, error) {
	var toolArgs map[string]interface{}
	if req.Params != nil && req.Params.Arguments != nil {
		if err := json.Unmarshal(req.Params.Arguments, &toolArgs); err != nil {
			return nil, fmt.Errorf("failed to parse arguments: %w", err)
		}
	} else {
		// No arguments provided, use empty map
		toolArgs = make(map[string]interface{})
	}

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