fix: improve HTTP 500 error messages with detailed error information

[observerw]

Summary

Fixes issue 3.2 from lsp_test_report_spring_boot.md - Frequent HTTP 500 Internal Server Errors with empty error messages.

Problem

When using the LSP CLI with large Java projects (like Spring Boot), HTTP 500 errors occurred frequently with completely empty error messages (Error: ), leaving users with no information about what went wrong.

Root Cause

1. Exceptions from the LSP server (especially ExceptionGroup errors) were being caught by a generic handler
2. The handler simply returned str(exc), which produces unhelpful output for nested exceptions
3. Error extraction from HTTP 500 responses wasn't pulling detailed information

Changes

Modified Files

1. src/lsp_cli/manager/client.py - Enhanced the exception handler to:

   • Recursively extract errors from ExceptionGroup
   • Return structured error data with error_type, detail, and request_path

2. src/lsp_cli/cli/shared.py - Improved error message formatting to:

   • Extract and display error type and endpoint
   • Format as: [ErrorType] at /endpoint: detailed message
   • Handle JSON parsing failures gracefully with specific exception types

Results

Before:

Error: 

After:

Error: [NotFoundError] at /capability/hover: Symbol ['29:14'] not found in /Users/wangbowei/workspace/spring-boot/buildpack/spring-boot-buildpack-platform/src/main/java/org/springframework/boot/buildpack/platform/docker/LoadImageUpdateEvent.java

Testing

• ✅ Tested with Spring Boot project that previously produced empty errors
• ✅ Verified clear, actionable error messages are now displayed
• ✅ All linter checks pass
• ✅ Code formatted with ruff

Impact

Users now receive clear, actionable error messages that explain:

• What went wrong (error type)
• Which endpoint failed (request path)
• Specific details for debugging (detailed message)