Problem

Streaming/block-flush replies can include 1-2 blank lines before the actual response text when extended thinking is enabled.

Steps to reproduce

1. Use an Anthropic model with extended thinking enabled.
2. Send a message over a channel that uses the streaming/block-flush path (for example, iMessage).
3. Observe the assistant reply.

Expected behavior

Replies should start with the intended text with no leading blank lines.

Actual behavior

Replies sometimes begin with one or more blank lines before the content.