fix: keep reasoning out of the reply body

A delta carrying both reasoning_content and an empty content was
classified by truthiness, so the reasoning fell through to the content
branch. The tail of the model's thinking was stored and displayed as the
answer, splitting mid-sentence across the two fields.

Classify on the presence of the field instead, and return nothing for an
empty reasoning delta rather than falling through.

The visible symptom was a code block swallowing the message: leaked
thinking is dense with backticks, and an odd count leaves a run open to
the end of the reply. Close an unterminated fence before parsing, with a
closer matching the opener's length, and drop a lone dangling inline
backtick. Streaming needs this regardless, since a fence is unclosed on
nearly every frame.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

0 files changed, 0 insertions, 0 deletions