btw

btw is an external plugin for DeepSeek Harness (DSH), the desktop coding-agent app. It adds parallel side chats to the right sidebar of any DSH conversation. A side chat runs beside the main thread, inherits its workspace, tools, permissions, model, and reasoning effort, and starts with a digest of the main conversation. The side-chat tab renders the shared conversation surface, so composing, queuing, attachments, tool cards, Markdown, and scrolling behave exactly like the main thread.

Requirements

• DeepSeek Harness 0.2.1-rc.1 or newer (the engines.dsh floor in package.json).
• A DSH profile to install into; the desktop profile is shown below.
• btw is not a standalone app: the host half runs inside the DSH host, and the client half is a DSH Web client plugin. It plugs into DSH's resources, sessions, sidebarRightTabs, sidebarRight, slots, commandUi, shortcuts, and locale services, and renders DSH's shared conversation.content factory.

How it works

• A side chat is an ordinary hidden Session: meta.parentSession records lineage, and the session is archived right after creation, so it stays out of the session lists.
• The client does not paint a custom chat panel. Each side chat is a resource tab:
• address: dsh-resource://btw/session/?parent=
• the resource provider calls /attach first (so the child Agent is live), refreshes the session catalog, then sessions.retain()
• the tab body binds the child with SessionProvider and renders conversation.content with variant: 'embedded'
• therefore the composer, image paste/attachments, queued messages, tool cards, thinking, Markdown, and scroll-follow all come from the main-thread components
• Archive and sending: the shared Composer prompts the child session directly. A prepended agent/pre-step listener unarchives the child before the archived-session gate runs; agent/status re-archives it once the agent is idle.
• Context is injected as system-prompt sections: at fork time the host reads the parent transcript, keeps roughly the last 10 messages / 6000 characters, and adds btw:context (interpolate: false) plus btw:role. Reattaching a chat re-reads the parent and refreshes the digest.
• Inheritance: agentPresets.composeFrom(agentCtx, parent.ctx) copies tools and prompt sections; permissionPresets copies the access policy; the model route comes from the parent's request/header (falling back to agentDefaultModel). The child is accounted into the parent's Workspace and seeded with a model/selection event so the shared composer does not ask for a workspace and shows the same model/effort.
• Many side chats per main conversation: one tab per chat; GET /state lists them all. A tab's × runs registerCloseHandler and closes the chat (dispose + tombstone), so it never comes back after a restart.
• Restart recovery: /state re-registers every btw-* child of the parent from disk (skipping tombstones). The resource calls /state before /attach; attach resumes the agent with composeFrom and the context sections, so a resumed side chat keeps the same tool surface.
• Tombstones live in ~/.dsh/btw/closed.json (honoring DSH_HOME).
• Delivery between sessions uses agent tools, not HTTP:
• send_to_main (side chat) sends [side chat ] ... to the main conversation as a user message.
• send_to_side (main thread) sends [main thread] ... to the most recent side chat, or to childId when given.
  Both call followup in-process; there is no loopback delivery route.
• The client depends only on react; everything else comes from cordis services (resources, sessions, sidebarRightTabs, sidebarRight, slots, commandUi, shortcuts, locale).

Install

dsh plugin --profile desktop add /path/to/btw

After changing code, run pnpm build and restart the app. The host snapshots client bundles at boot, so reloading the page is not enough.

Usage

UI copy comes from the DSH locale service (zh/en) and follows the app language; it is not hardcoded in the component.

• ⌘⌥S, /side, or /btw: open the most recent side chat; create one when none exists.
• The + in the tab header starts another side chat.
• Closing the tab's × closes and deletes that side chat.
• The tab title follows the session title after the first message; before that it reads "Side chat".
• The main thread can call send_to_side; a side chat can call send_to_main.

Limits

• The context is a snapshot taken at attach time; later messages in the main conversation are not synchronized automatically.
• DSH's session persistence layer has no delete API, so closing a side chat only disposes the agent and writes a tombstone; the btw-* log stays under ~/.dsh/sessions.
• Host routes accept loopback requests only.

Development

pnpm install
pnpm typecheck
pnpm test
pnpm build