The browser
Pages open as tabs on the system WebView: the project's own pages, a dev server, or any site. You and an agent look at the same page.
A page
A page has its own toolbar: back, forward, reload, the address field, its size and comments. The address field knows the project's pages and its history. ⌘L goes to it, ⌘R reloads, ⇧⌘O opens the page in your default browser.
A page that never comes, such as a dev server that has stopped, says so in one line and keeps its address, so ⌘R tries it again.
Sizes
⇧⌘M sets the page's size: a phone, a tablet, or the tab's whole width. An agent sets it with size in the window tool.
Comments
⇧⌘C pins a comment to an element of the page; ⌘↩ sends it. The agent hears it after its next call, under "What the person sent from the window", so you can point at what is wrong instead of describing it.
The project's files
A file or a directory of the project opens as a page, served on loopback under an unguessable prefix: no dot-files, and nothing outside the project. Only http and https load besides. Security says what a page can and cannot do.