# @deepseek-ai/dsh-client-connection

English | [中文](README.zh.md)

Wire consumer layer: the client plugin's apply mounts `ctx.connection` (shared api client + current-page loopback state + observable generation-scoped `hostDescription` + single-consumer stream-loop starter); the export face carries the wire contract types, the `AbstractApiClient` abstraction, and the loop's sink/config types. Each successful readiness handshake publishes the exact `host.describe` value before `onConnected`; generation loss and explicit stop clear it, so native-capability consumers never retain a disconnected answer. The browser carrier uses HTTP POST for unary and respond operations and opens one downlink-only WebSocket each for `events.mux` and `events.host`; the in-process carrier satisfies the same two-stream abstraction. The Host half owns the single `/api` route and its Fetch bridge; a registered Typert interceptor claims its Remote endpoints before the API Proxy fallback. Loopback hostname classification stays package-internal: the `/api` Host fence and WebSocket upgrades use it directly, while other client plugins consume the derived `ctx.connection.isLoopback` state. The node half's `/api` route pins the privileged method set (`host.pickDirectory`, `host.openPath`, and the whole configuration plane — `settings.describe`/`openDocument`/`update`/`replace`/`mutate` and `credentials.describe`/`set`/`unset`; reads and native actions included, since describing returns the exposed configuration, opening acts on the Host desktop, and probing an arbitrary reference reports where a credential comes from — and the agent-preset authoring plane, `agentPreset.read`/`copy`/`openDocument`/`remove`, since a composition names the plugins a session runs, so reading one is reconnaissance, and copy/remove/openDocument manage the roster and drive the host desktop (authoring is copy-only, so none of them accepts composition text or a path); `agentPreset.list` and `agentPreset.select` stay out — the roster carries only ids and trust, and choosing a preset grants nothing `session.create`'s own `agentPreset` did not, over a default that already carries bash) to loopback by passing the trust fence with an empty trust list — a declared `trustedHosts` authority reaches every other method, while these stay loopback-local until a real authentication layer exists. The platform carriers and ConnectionController loop are package-internal; apply selects and drives them. The downlink boundary is documented in the [WebSocket downlink carrier Agent Note](../../../.agents/notes/implemented/architecture/2026-08-04-websocket-downlink-carrier.md).

## /api browser-trust fence

The node half guards every entry under `/api` before bridging or upgrading (`src/api-request-trust.ts`). Every request — browser-marked or not — must present a `Host` that is a loopback authority or matches a `trustedHosts` entry: exact on `host:port` entries, any port on port-less entries, both sides compared through WHATWG normalization (DNS-rebinding defense). There is deliberately no shortcut for unmarked HTTP requests: over plain HTTP a browser attaches neither `Origin` nor Fetch-Metadata to image and navigation reads, so an unmarked request may still be a rebound browser read with a readable response, and Host is the one header rebinding cannot forge; a browser WebSocket handshake carries `Origin` and passes the same comparison. Non-browser clients pass the same fence via loopback, deployment-derived LAN IP literals, or a declared authority. When markers are present, an attached `Origin` must equal the Host authority, and an explicit `sec-fetch-site: cross-site` marker is refused. A `trustedHosts` entry that is not a bare, canonical `host[:port]` authority — one WHATWG parsing reads back exactly as written — fails the plugin load loudly: parsing would otherwise quietly authorize the hostname inside `harness.internal/path`, or broaden a dangling-colon or zero-padded port to an any-port grant. HTTP failures answer plain 403 before any RPC dispatch; upgrade failures reject the handshake before any event stream starts. Non-loopback compositions must trust their serving authorities explicitly: the Web runtime derives LAN IP literals from an all-interfaces server config, while `trustedHosts` in cordis.yml and the CLI's `--trusted-host` flag declare named authorities. `dsh web --host 0.0.0.0` is intentionally unsupported until remote access has an authentication layer. The fence is a reachability policy, not authentication; the Web carrier provides no authentication layer. Decision record: [the api browser-trust boundary Agent Note](../../../.agents/notes/implemented/architecture/2026-07-28-api-browser-trust-boundary.md).

## `/api` WebSocket downlinks

`/api/events.mux` and `/api/events.host` each accept a WebSocket upgrade and send only the corresponding `ServerRequest` text messages to the browser; the client sends no application data over these sockets. If either socket ends, the current connection generation fails and rebuilds both streams; readiness still requires both sockets to be open and the `host.describe` HTTP call to succeed. Host teardown terminates both sockets, aborts their sources, and waits for source cleanup before returning. Ordinary network GETs to these paths return 426 with no SSE fallback; `toFetchHandler`'s SSE codec serves only the isomorphic in-process carrier.

## Model Experience

None, as the wire consumer layer moves already-composed messages between browser and host; nothing here reaches a model request.

#### KV Cache effect

None; this package neither assembles nor sends a provider request.

## Known Limitations and Deferred Work

- **History resumes an unattached session** — opening history may create the host-side agent and add latency to the first open; there is no persistence-only read path.
- **The `/api` bridge buffers each request body in memory** — `maxRequestBodyBytes` (default 160 MiB, sized for the default 100 MiB aggregate image limit after base64 expansion plus envelope headroom) is therefore also the per-request resident bound; a streaming body path would be needed to lower it without shrinking the image limits.
