* feat: handle error from the initialize middleware
In some situation, the initialize middleware can check the status of the
server and decide to raise an error.
Example use case: in a FastMCPProxy, an initialization middleware
overrides the on_initialize method and connect to the underlying proxied
client. When client respond with error, I want to pass this error to the
client.
* docs update
* test: use McpError assertions now that exception propagation is fixed
- Update tests to catch McpError specifically instead of generic Exception
- Remove commented-out code in low_level.py
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Co-authored-by: Jeremiah Lowin <153965+jlowin@users.noreply.github.com>
Wrap responder.respond() to capture the InitializeResult before it's
sent to the write stream, then return it through the middleware chain.
This allows middleware (e.g., logging) to access the server's initialize
response, not just the client's request.
