## Why
OAuth metadata discovery for an optional HTTP MCP server can stall, delaying
`thread/start` even though that server is not required.
## What changed
- Remove eager MCP authentication-status discovery from session and connection
manager startup.
- When an MCP connection reports an authentication error, inspect configured and
stored credentials locally to preserve login and reauthentication failure
reasons without making another discovery request.
- Continue using server configuration directly for startup error messages and
timeout hints.
## Testing
Add an app-server regression test with an optional HTTP MCP endpoint that accepts
a connection but never responds, and verify that `thread/start` completes without
waiting for its configured startup timeout.
GitOrigin-RevId: 56fe0188cc1ceaf746b0b65e8b7dd1fd2e13420d
jif
2e156cbe31