fix: refresh props for existing Durable Objects via serveSSE POST endpoint

[asghar-mir]

Fixes #323

Problem

When using a MCPAgent locally, the POST /message handler fetches the Durable Object using idFromName("sse:${sessionId}") but does not re-initialize or update the props context via _init() or similar.

This leads to stale or missing values inside this.props. For instance, in the Auth0 integration example, this.props.tokenSet.accessToken from tokenExchangeCallback never updates after the first token exchange. Even though the refresh token flow is correctly triggered, the updated access token never reaches the Durable Object instance, breaking authenticated API requests.

Solution

Added a call to await doStub._init(ctx.props) before forwarding the request to the Durable Object in the POST /message handler. This ensures that the Durable Object instance has the latest props context, including updated access tokens from OAuth refresh flows.

Testing

• All existing tests pass
• The fix follows the same pattern already used in the GET handler for initial SSE connections
• No breaking changes to the API

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Latest commit: d4d5f4b

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