richText messages only kept rich_text_list items whose type was
"text", so bold/italic/inlineCode/pre segments were silently dropped;
a message made entirely of formatted segments produced empty content
and fell through to the "unsupported message type: richText" warning.
Now any item carrying text is kept (matching the SDK's own
get_text_list, which keys off the "text" field) and its type is mapped
to Markdown so the formatting survives into the agent's context.
Text and downloadCode within a rich-text item are handled
independently (the SDK treats them as separate via get_text_list /
get_image_list), so an item carrying both a caption and an attachment
no longer drops the file.
The shared httpx.AsyncClient was created without a timeout, so all
requests (including large file/image downloads) used httpx's 5s
default and hit ConnectTimeout/ReadTimeout on uploads. Set an explicit
httpx.Timeout (connect=10s, read/write=30s).
Adds regression tests for formatted-segment preservation, the
all-formatted no-drop case, the text+downloadCode item, and the client
timeout configuration.
Closes#4497
Max HsuandXubin Ren
638af123ba