Unable to assign handlers to McpServerOptions.Handlers after upgrading to v0.9.0 (readonly regression?)

[gabaoalb]

Describe the bug
After upgrading from v0.8.0 to v0.9.0, it is no longer possible to assign handlers to McpServerOptions.Handlers. The property now appears to be readonly, which prevents configuring custom handlers as demonstrated in the documentation/examples.

To Reproduce
Steps to reproduce the behavior:

1. Upgrade the library from 0.8.0 to 0.9.0
2. Attempt to implement the "fine-grained control" example from the GitHub repository
3. Assign a value to McpServerOptions.Handlers

Expected behavior
McpServerOptions.Handlers should remain assignable so that MCP servers can define custom tool handlers. This configuration is required for dynamically handling tool calls made by the LLM.
In my use case, the MCP server retrieves data from an external API and dynamically assembles tool behavior based on an OpenAPI JSON schema. Preventing handler assignment blocks this workflow entirely.

Logs

Additional context

• It changed from version 0.8.0 to 0.9.0
• No relevant code changes on my side besides the version bump
• I'm not sure if I could set a handler in any other way than what's shown in the examples.

[jeffhandley]

Thanks, @gabaoalb. This was an intentional change but we will reevaluate based on your feedback here and determine if we should restore the setter or provide a different approach to achieve this scenario.