- Remove _getHttpResponseCompleted and rely on _httpSseWriter being null as the signal that the GET response stream has been released. Null out _httpSseWriter in DisposeAsync so SendMessageAsync correctly skips writing post-dispose.
- Replace the dispose-idempotency role of the old flag with a dedicated _disposed bool.
- Move the explanatory comment in SendMessageAsync onto the event store branch (which intentionally still runs when the response stream is gone, to support Last-Event-ID replay).
- Rewrite the unit test to assert observable behavior via a recording Stream instead of reflecting on private fields.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>