- Bump mcp SDK to >=1.23.1
- Add `client_secret_basic` authentication support (SDK PR #1334)
- TokenHandler now wraps SDK's handle() to transform `unauthorized_client`
to `invalid_client` on 401 responses per OAuth 2.1 spec
- Update `sample()` return type to use SDK's SamplingMessageContentBlock
- Update test expectations for new SDK fields (`task`, `_meta`)
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Co-Authored-By: Claude <noreply@anthropic.com>