dsh-markdown-preview

In-chat preview for produced files in DeepSeek Harness Web.

By default, clicking a produced-file chip in the DSH Web GUI hands the file to
the operating system's default application (open on macOS → Xcode for many
extensions). This plugin takes over the produced-files row and makes the click
render the file right in the conversation — Markdown is rendered with
markdown-it + highlight.js server-side, images preview inline, code
files (JSON / JS / TS / Python / YAML / …) open in a dark syntax-highlighted
code view, and any other text file shows as plain text. The old behaviors
stay one click away: open in the system app, or reveal in the folder.

Features

• Click a produced-file chip → inline preview, no native app, no new tab.
• Markdown rendered properly (GFM tables, fenced code, blockquotes, links,
  hard line breaks) with syntax highlighting in code fences
  (highlight.js common languages).
• Code-file preview with full syntax highlighting (v0.3.0): 40+ extensions
  (.json .js .ts .py .yml .sh .css .html …) render in a dark
  editor-style view with GitHub-Dark token colors, highlighted server-side.
• Fullscreen viewer (v0.3.0): one click expands the preview — Markdown,
  image, code, or plain text — to a full-viewport overlay with the toolbar
  kept on top; close with the button or Esc.
• Image preview (PNG / JPEG / GIF / WebP / SVG) as data URLs — no extra
  route. SVG is safe to inline: browsers never execute scripts inside SVG
  loaded through an <img> element.
• Plain-text fallback for every other text file; binary files are sniffed and
  refused with a clear message.
• Panel header with file size, fullscreen, copy content, open in
  system app, and collapse.
• 1 MiB cap for text / 4 MiB for images, with an explicit truncation notice.
• Keeps the stock experience: chips, "+ N files", and "Show in folder" still
  behave as before, and inline code-mentions of produced files stay clickable.
• Theme-aware preview panel: background, body text, links, code and error
  colors all use real DSH theme variables (v0.1.1 fixes unreadable text on the
  always-white background in dark mode).

Install

dsh plugin --profile web add dsh-markdown-preview

Restart dsh web. Requires pnpm on PATH (dsh plugin forwards to pnpm) and
DSH >= 0.1.0-rc.6.

Usage

Nothing to configure. After restart, any turn that produced files shows the
familiar produced-files row; clicking a chip toggles the preview panel.

How it works

• Host half (lib/index.js): registers a /preview RPC channel on
  ctx.connection with the loopback trust authority (the same
  DNS-rebinding / cross-site fence the /api surface uses). read returns
  the file — Markdown rendered to escaped HTML (markdown-it with
  html:false, safe-link policy), images as base64 data URLs, code files
  highlighted server-side (hljs by extension, 40+ languages), other text
  capped at 1 MiB with a binary NUL-byte sniff. open proxies the stock
  host.openPath so the native-app action is exactly the official one.
• Client half (lib/client.js): a standard dsh.client bundle. It owns
  the deliverables conversation-event kind and the
  conversation.chat.turnTail slot (the official ui-deliverables row is
  disabled by this bundle's patch; its prompt section and the
  chatFileMentions service are re-provided here), so the replacement is
  behavior-compatible, not a DOM hack.
• Rendering happens on the host, keeping the browser bundle thin and
  dependency-free.

Compared to similar plugins

Security notes

• The channel is loopback-only and behind the connection trust fence.
• Markdown is rendered with html:false; raw HTML in a document is escaped,
  and links are limited to http(s)/mailto/# by markdown-it's default
  validateLink.
• Preview caps and binary sniffing prevent accidental memory/UI abuse; the
  preview is read-only (no write endpoint).

Uninstall

dsh plugin --profile web remove dsh-markdown-preview

Development

git clone https://github.com/GitHubJiKe/dsh-markdown-preview.git
cd dsh-markdown-preview
npm install          # markdown-it + highlight.js for the host half
dsh plugin --profile web add file:$(pwd)
# restart dsh web; the profile symlinks your working copy, so edits to
# lib/ apply after another restart (client bundles are scanned at boot)

License

MIT

Changelog

• v0.3.0 (2026-08-17): Code-file syntax highlighting + fullscreen viewer.
  read now serves 40+ code extensions (.json .js .ts .py .yml
.sh .css .html …) as a new code kind with server-side hljs
  highlighting rendered in a dark editor-style view (GitHub-Dark token
  colors); markdown fenced code blocks also gained real token colors (they
  previously had transparent-only hljs styling). The panel header adds a
  fullscreen action: the preview — markdown, image, code, or plain text —
  opens in a fixed full-viewport overlay that keeps the toolbar (copy /
  collapse replaced by close) and exits via button or Esc.
• v0.2.0 (2026-08-16): SVG preview support + workspace-relative path
  resolution. .svg joins the inline image set (safe: <img> never runs
  embedded scripts), and relative produced-file paths now resolve against the
  registered workspace roots instead of the host process cwd, fixing ENOENT
  for workspace-relative files.
• v0.1.1 (2026-08-15): Fix unreadable preview text in dark mode. The panel
  used the non-existent --dsw-alias-surface-raised variable, so its background
  was always white while body text inherited the chat area's light dark-mode
  color. Background/text/link/error colors now use real theme variables
  (--dsw-alias-bg-layer-1, --dsw-alias-label-primary,
  --dsw-alias-brand-primary, --dsw-alias-state-error-primary), so the panel
  follows light/dark themes automatically.
• v0.1.0 (2026-08-15): Initial release.