A toggle in the chat's app bar; when on, every message describes what it would
do and changes nothing. A finished plan grows two buttons: approve and run it,
or revise it.

Approving resumes the same Claude session with plan mode off, so the plan is
context rather than a second question. Revising just seeds the composer, because
the useful correction is almost always a sentence, not a new prompt.

The approve bar appears only under the newest assistant turn, only when that
turn actually ran as a plan, and only once it has finished — offering to approve
something still being written would approve a plan nobody has read.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>