fix: propagate error messages in /mcp endpoint responses

[jonathan-fulton]

Summary

Fixes error propagation in the /mcp endpoint tool invocation handler.

Problem

When using server/<server-id>/mcp endpoint for tool invocations, exceptions (e.g., 401 unauthorized errors) resulted in empty responses instead of actual error messages.

The previous code caught all exceptions and returned an empty list:

except Exception as e:
    logger.exception(f"Error calling tool '{name}': {e}")
    return []

Solution

Re-raise exceptions after logging so the MCP SDK can properly convert them to JSON-RPC error responses:

except Exception as e:
    logger.exception(f"Error calling tool '{name}': {e}")
    raise

This ensures clients receive proper error messages instead of empty results.

Testing

Verified that errors are now properly returned in the response body instead of empty results.

Fixes #2570

[crivetimihai]

Thanks @jonathan-fulton! Important fix - swallowing exceptions and returning empty results was definitely masking real errors from clients. Re-raising to let the MCP SDK convert them to proper JSON-RPC error responses is the right approach. I'll start merging and rebasing.