EnsureSuccessStatusCode throws without the response body, making server error diagnostics difficult when the body contains error details (e.g., 400 Bad Request with validation messages).

Changes

• New HttpResponseMessageExtensions in src/Common/:

  • EnsureSuccessStatusCodeWithResponseBodyAsync() - reads body before throwing (with 5-second timeout to prevent hangs)
  • CreateHttpRequestException() - constructs exception with body in message
  • Catches all exceptions when reading response body (including cancellation) to ensure the HTTP error is always thrown
  • Truncates large response bodies to 1KB for readability

• Updated transport clients to use the new method:

  • SseClientSessionTransport (connect + send)
  • StreamableHttpClientSessionTransport (send)
  • ClientOAuthProvider (token exchange + metadata fetch)

Result

Before:

HttpRequestException: Response status code does not indicate success: 400 (Bad Request).

After:

HttpRequestException: Response status code does not indicate success: 400 (Bad Request). Response body: {"error":"invalid_grant","error_description":"Authorization code expired"}

HttpRequestException.StatusCode is preserved on .NET targets.

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