[FEATURE] Mods: a pane element that renders a local web page (WebView), no server needed

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

Mod panes (function-hooks plugins, $.ui.open + ui.render) can't show a web page. The desktop element table is Box, Text, Button, Input, Select, Svg, Link, Code, Markdown and Client: Svg is script-less and Client is cell-based. So any UI that needs real web features (a canvas, image display, drag and drop) can't live in the mod's own pane. Today the workaround is to have the mod start a local HTTP server and open the page in the browser pane, which means writing and running a server just to show a page.

Proposed Solution

A built-in pane element that renders a page from the plugin's own folder, e.g. WebView({ source: './ui/index.html' }): sandboxed, no server needed, and talking to the hooks module by messages (like Client posts). Mod UIs could then be built with ordinary web tooling (TypeScript with React, Angular, Svelte ...) instead of composing pane elements.

Alternative Solutions

• Start a local server from the mod ($.process.spawn) and open it in the browser pane. Works, but needs a server, and a mod can't open the browser pane on its own in auto mode (separate issue), so Claude has to be asked to do it.
• Svg with an embedded picture: no scripts, 128 KB limit, so no interaction.

Priority

Medium - Would be very helpful

Feature Category

Developer tools/SDK

Use Case Example

A picture-review mod for flashcard images: the user looks at each generated picture, marks it ok/off, draws red marks on what is wrong, and sends a batch; the mod turns the batch into a turn for Claude ($.prompt.submit), which fixes the marked pictures. The event part works great; the drawing UI needs a canvas, so it has to run in a separate local server shown in the browser pane.

Additional Context

Claude Code 2.1.286, desktop app, Windows.