[atesgoral]

Motivation and Context

When an HTTP server-request handler raised an unexpected exception, the client sent the exception message back to the server. Messages can hold local paths and other application details that the server should not receive. The client now sends -32603, Internal error, and writes the exception class and quoted, escaped message to local stderr. String#dump keeps control characters from creating or recoloring log lines. Explicit ServerRequestError responses are unchanged. This matches the server-side fix in #486. I used stderr instead of a new reporter callback to keep the transport API unchanged.

Fixes #660.

How Has This Been Tested?

test/mcp/client/http_test.rb. The regression expects an exact generic error body instead of the handler's message. The handler raises server-request text containing a newline and a terminal escape sequence; stderr must keep that text quoted and escaped on one line. The changed regression fails on the previous PR head because it writes the control characters raw. It passes with this change, including under Rake's -W0 -W:deprecated flags.

The HTTP client test file passes (143 runs, 432 assertions), and so does the full suite (2,500 runs, 8,266 assertions). RuboCop is clean on the changed files.

Breaking Changes

None. Responses to unexpected handler exceptions carry a generic message instead of the exception text. Intended ServerRequestError replies are unchanged.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed