Fixes#43322
* fix(feishu): clear stale streamingStartPromise on card creation failure
When FeishuStreamingSession.start() throws (HTTP 400), the catch block
sets streaming = null but leaves streamingStartPromise dangling. The
guard in startStreaming() checks streamingStartPromise first, so all
future deliver() calls silently skip streaming - the session locks
permanently.
Clear streamingStartPromise in the catch block so subsequent messages
can retry streaming instead of dropping all future replies.
Fixes#43322
* test(feishu): wrap push override in try/finally for cleanup safety
c6e32835d4