App Content Zoom

App content zoom is an OS runtime readability feature for sub-app windows. It is not browser page zoom and it is not window resizing.

User Model

Each app window can keep its own zoom level:

• 80%
• 90%
• 100%
• 110%
• 125%
• 150%

The titlebar exposes a zoom control next to refresh and translation. The menu offers zoom in, zoom out, reset zoom, direct level selection, an "Apply to this app" placeholder, and a future default app zoom setting placeholder.

Keyboard shortcuts operate on the active app window:

• Cmd/Ctrl + + or Cmd/Ctrl + =: zoom in
• Cmd/Ctrl + -: zoom out
• Cmd/Ctrl + 0: reset to 100%

The shell shows a small toast such as App zoom: 125% when the state changes.

Runtime Boundary

Local module apps should prefer CSS variables, root classes, font scale, density tokens, or app-aware layout changes. The current shell-level implementation applies a per-window content zoom wrapper so the feature is immediately available, but long-term production apps should opt into cleaner density-aware rendering.

Iframe apps are different. Scaling an iframe wrapper can affect pointer geometry, text crispness, and embedded layout assumptions. The v0 shell may show the control and apply a wrapper-level best effort, but the durable direction is an app runtime protocol:

• os:set-app-zoom
• app:zoom-supported
• app:zoom-changed

Standalone or iframe apps should eventually report whether they support app zoom and apply the zoom internally through their own document styles.

What It Is Not

App content zoom does not change the browser's global zoom. It does not resize the app window. It does not replace responsive design. It is a per-window readability and density control managed by the OS shell.