Think

Pass title for the header and the reasoning as children, and click the header to fold or unfold it.

Set loading while the model is still thinking to show a spinner, and blink to make the title shimmer.

Set defaultExpanded to false to start folded, so the reader opens the reasoning only when they want it.

Hold expanded in state and update it from onExpand, so a button outside can fold or unfold the reasoning too.

An assistant reply in a Bubble, with the folded reasoning above the answer.

A research panel where the reasoning runs open while the model thinks, folds when it is done, and the answer streams in below.

An algebra tutor that solves an equation with its worked steps open in the reasoning, followed by the answer and follow-up buttons.

A support ticket where the assistant checks the billing history in folded reasoning before suggesting a reply to send.