dsh-chat-offscreen

Keep long DeepSeek Harness (DSH) Web chat sessions responsive.

The problem

The DSH chat transcript is not virtualized upstream: every loaded history page stays in the DOM. Backwards paging pulls 50 messages per loadOlder() page, and the turn rail's jump loader pulls 200-message pages until the window covers the target — with no eviction. On a long session, dragging the transcript width handle, the sidebar divider, or simply scrolling forces layout + paint across thousands of nodes, which makes the UI stutter.

What this plugin does

It is a tiny client-side plugin that installs one stylesheet:

[data-chat-flow-kind="assistant-step"]:not(:has(.md-table-wide)),
[data-chat-flow-kind="tool-call"]:not(:has(.md-table-wide)) {
  content-visibility: auto;
  contain-intrinsic-size: auto 120px;
}
[data-chat-flow-kind="assistant-step"]:has(.md-table-wide),
[data-chat-flow-kind="tool-call"]:has(.md-table-wide) {
  content-visibility: visible !important;
  contain: none !important;
}

content-visibility: auto lets the browser skip layout and paint for off-screen assistant steps and tool calls — a cheap approximation of virtualization — while contain-intrinsic-size: auto 120px keeps the scroll range stable and remembers a row's measured height once seen. Rows containing a wide markdown table opt out so their breakout width is never mis-estimated.

This is a rendering-layer workaround, not a data change: no messages, session events, or host state are touched. It composes with the retired @linxin666/dsh-perf P0 rule of the same shape.

Install

dsh plugin --profile web add github:publieople/dsh-chat-offscreen

Then restart the web profile (dsh web ...) and hard-refresh the page (Ctrl+Shift+R). The lib/ build is committed, so no package build script runs and no allowBuilds entry is required.

The bundle patch inserts the plugin row automatically. If you install by hand:

cd "$DSH_HOME/profiles/web"
pnpm add github:publieople/dsh-chat-offscreen

then add dsh-chat-offscreen to dsh.profile.bundles in that profile's package.json and restart.

Verify

Open a long session and drag the transcript width handle / sidebar divider, or scroll fast. In DevTools → Elements, an off-screen assistant step should carry content-visibility: auto.

Disable / uninstall

dsh plugin --profile web remove dsh-chat-offscreen

then restart. Removing the plugin removes the stylesheet; nothing is persisted.

Compatibility

• Client platform: web. Host half is intentionally empty.
• Depends only on the browser content-visibility feature (Chrome/Edge 85+, Firefox 125+, Safari 18+). On older engines the rules are inert and the UI simply stays as before.
• Built against DSH 0.1.5-rc.1; the plugin uses no DSH runtime imports.

Development

npm install
npm run typecheck
npm run build     # tsdown -> lib/index.js (ESM) + lib/client.js (ModuleLoader)
npm test          # drives the built client bundle against a fake DOM

lib/ is committed on purpose so Git installs need no build step. If you change src/, re-run npm run build and commit the result.

If upstream virtualizes the chat

When the DSH chat surface gains real virtualization, delete this plugin row. The upstream trajectory view (ui-trajectory) is already virtualized; the chat surface is not.