[FEATURE] Cowork: draw mod UI (band, pane, spinner) like the Code tab does

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

Mods are great in the CLI and the Desktop Code tab. In Cowork the hooks run, but nothing a mod draws ever shows up.

The mods docs already say cloud sessions run hooks but don't draw, so this isn't a bug report. But Cowork lives in the same desktop app that draws mods for the Code tab, and since Oct 6 Cowork on Pro/Max only runs in the cloud. So for me that's all of Cowork, which is where I spend most of my day.

What I saw in a Cowork task (Claude Code 2.1.296) with the repro below:

• session.start fires and $.fs.write works, so the mod is loaded and running
• $.session.surfaces() returns []
• the AbovePrompt hook ran 0 times across 2 turns
• no band, no toast, no status line

Proposed Solution

Code tab parity: AbovePrompt, Pane, Spinner, toast and status line in Cowork tasks. Raster and Image are terminal only anyway.

The mods types already describe remote surfaces drawing over the wire (ui_render), so I'm guessing some of the plumbing is there.

Alternative Solutions

• Run the mod in the Code tab or the CLI instead. Works, but it's not Cowork.
• Fall back to $.ui.log or a command's text reply. Fine for info, useless for anything visual.

Priority

Low - Nice to have

Feature Category

Developer tools/SDK

Use Case Example

I'm building a mascot mod (a cartoon chili pepper, it's dumb, it's fun) that sits in the band above the prompt and reacts to Claude: nervous on permission prompts, facepalm when a command fails, cheering when tests pass. In Cowork it's invisible. Same deal for the boring useful stuff, like a context or rate limit band. Similar ask for the VS Code panel: #99401.

Repro plugin, hooks/register.js (passes claude plugin validate):

let renders = 0

async function save($) {
  const surfaces = await $.session.surfaces()
  await $.fs.write('/tmp/cowork-draw-probe.json', JSON.stringify({ surfaces, renders }))
}

export function register(on) {
  on('session.start', async ($, e, next) => {
    const out = await next(e)
    $.ui.toast('toast works')
    $.ui.status('status line works')
    await save($)
    return out
  })

  on('ui.render', { component: 'AbovePrompt' }, async ($, e, next) => {
    renders += 1
    await save($)
    if (e.props.hasSurvey) return next(e)
    const { Text } = $.ui.resolve(e)
    return Text({ children: ['band works on ' + e.surface] })
  })
}

• Ghostty, claude --plugin-dir ./cowork-draw-probe (2.1.296): the band reads "band works on terminal", and the toast and status line show up.
• Cowork task (2.1.296, loaded by asking Claude to write the mod into the session's mods folder and enabling hot reload): no band, no toast, no status line, and the file says {"surfaces":[],"renders":0}.

Desktop app version: 2.31226.1