Page control
The agent reads and drives your live page, then persists to source.
The agent works against the page you see. It takes a snapshot of the accessibility tree, acts on an element, waits for the page to settle, and snapshots again.
Grab an element to point at what you mean: the crosshair in the composer picks any element on the page and pins it to your next message, source location included.
Preview, then persist
It can tweak the DOM and CSS live to show you an idea right away. These live edits are ephemeral. The next hot reload wipes them, because they are not in your source.
When you keep a change, the agent edits the real files so it survives a reload. It can open the exact source file in your editor too.
Ask for something visible, like "make the heading larger". You see it instantly, then the agent offers to persist it as a real edit.