Enhance MCP error messages with actionable guidance for parameter validation failures

[Copilot]

• Explore repository structure and locate MCP server error handling code
• Identify error generation locations (mcp_server_core.cjs, safe_inputs_mcp_server_http.cjs)
• Review tool definitions in safe_outputs_tools.json
• Create enhanced error helper function with actionable guidance
• Integrate enhanced errors into mcp_server_core.cjs (2 locations)
• Integrate enhanced errors into safe_inputs_mcp_server_http.cjs (1 location)
• Add tests for enhanced error messages
• Run make build to sync JS changes
• Run make lint-cjs to validate JavaScript
• Run make recompile to recompile workflows
• Verify error messages work correctly with integration test
• Add demonstration script showing enhanced error format
• Run Go linting (make golint) - fixed formatting issue

Original prompt

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This section details on the original issue you should resolve

<issue_title>[plan] Implement enhanced MCP error messages with actionable guidance</issue_title>
<issue_description>## Objective

Improve MCP server error messages to include actionable guidance that helps agents self-correct when they make parameter validation errors.

Context

When agents call MCP tools with missing parameters, they receive generic errors like "missing or empty 'item_number'" without guidance on how to fix it. Enhanced errors should teach agents the correct usage.

Approach

1. Locate the MCP server error handling code (likely in actions/setup/js/ or pkg/workflow/js/)
2. Identify where parameter validation errors are generated
3. Enhance error responses to include:
   • Parameter name and what it represents
   • Expected format/type
   • Example of a correct tool call
4. Ensure error format is consistent across all MCP tools

Files to Modify

Search for:

• MCP server implementation files containing error handling
• Look for files with "MCP error -32602" or parameter validation logic
• Likely in actions/setup/js/*.cjs (source) or pkg/workflow/js/*.cjs (generated)

Example Enhancement

Current error:

MCP error -32602: Invalid arguments: missing or empty 'item_number'

Enhanced error:

MCP error -32602: Invalid arguments: missing or empty 'item_number'

Required parameter 'item_number' is missing. Please provide the numeric ID of the issue, PR, or discussion to comment on.

Example:
{
  "item_number": 123,
  "body": "Your comment text"
}

Acceptance Criteria

• All MCP validation errors include parameter description
• Errors include example of correct usage
• Error format is consistent across all safe output MCP tools
• JavaScript changes pass make lint-cjs validation
• Changes are synced to pkg/workflow/js/ via make build

Testing

After making changes:

make build           # Sync JS changes and rebuild binary
make lint-cjs        # Validate JavaScript code
make recompile       # Recompile workflows
# Test with a workflow that intentionally has validation errors

Related to #7950

AI generated by Plan Command for discussion #7934

Comments on the Issue (you are @copilot in this section)

• Fixes [plan] Implement enhanced MCP error messages with actionable guidance #7952

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[pelikhan]

@copilot format and lint

[Copilot]

@copilot format and lint

All JavaScript files are already properly formatted and pass linting checks (make lint-cjs passes). No changes needed - the code was formatted with Prettier during the initial implementation in commits 747275e and 476f820.

[pelikhan]

@copilot lint go

[Copilot]

@copilot lint go

Go linting now passes (make golint returns 0 issues). Fixed formatting issue in pkg/workflow/permissions_shortcut_included_test.go in commit 7e4e3c5.