fix: add existingSessionId option to WebStandardStreamableHTTPServerTransport for multi-node session hydration#1668

Vadaski wants to merge 4 commits intomodelcontextprotocol:mainmodelcontextprotocol/typescript-sdk:mainfrom

Vadaski:fix/1658-streamable-http-session-hydrationVadaski/typescript-sdk:fix/1658-streamable-http-session-hydrationCopy head branch name to clipboard