feat(mcp): structured error responses for agent coordination

[unicoderbot]

Summary

Implements structured error responses in the MCP server to provide agents with detailed failure context, partial results, and recovery suggestions. Error responses now follow a consistent JSON schema with:

• status: failure or partial_failure (if partial results exist)
• failureType: one of transient, validation, business, or permission
• attemptedAction: the tool name, command, directory, and arguments that failed
• reason: human-readable failure cause
• partialResults: any output captured before failure
• alternativeApproaches: context-aware recovery suggestions based on failure type

Changes

Core Implementation

• Added buildStructuredErrorResult() function to generate consistent JSON error payloads
• Added failureTypeForExitCode() to classify exit codes into semantic failure categories using sysexits.h conventions
• Added alternativeApproachesFor() to suggest recovery strategies per failure type
• Refactored _runToolCommand() to pass requestArguments through for error context
• Updated all tool handlers (_handleCreate, _handleTest, _handlePackagesGet, _handlePackagesCheckLicenses) to include request arguments

Error Classification

• validation: Bad input (exit codes: usage, data, noInput, config)
• permission: Access denied (exit code: noPerm)
• transient: Temporary failures likely to succeed on retry (exit codes: unavailable, tempFail, ioError, osError, osFile, cantCreate)
• business: Rule violations or unexpected outcomes (default for unknown codes)

Testing

• Updated 12+ test cases to validate structured error payloads instead of plain text
• Added comprehensive test coverage for failureTypeForExitCode(), alternativeApproachesFor(), and buildStructuredErrorResult()
• Verified partial results are preserved when output is captured before failure
• Confirmed JSON payload structure matches agent requirements

Closes #1615

[marcossevilla]

@vgvbot /address-review

[unicoderbot]

On it, I'll address the review comments and push the changes.

• Preparing environment
  • Cloning repository
  • Setting up dev environment
• Reviewing feedback
• Working on changes
• Pushing updates

I've pushed changes to address the feedback.