deepseek-harness/packages/host/apiproxy/README.md

@deepseek-ai/dsh-host-apiproxy

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The API gateway every client shape shares: the TS contract (src/api/, zero Node dependencies, importable from the browser), the fetch carrier pair (src/fetch/: toFetchHandler on the host side, AbstractApiClient plus platform subclasses on the client side), and the host-side implementation (src/api-proxy.ts: createApiProxy plus the default-exported ApiProxyService gateway plugin — config {provider, model, workspaceRoot?}, provides ctx.apiProxy). Transport-agnostic by design: this package registers no routes; carriers (HTTP today, IPC later) wrap ctx.apiProxy themselves. The shipped core composition lives in apps/cli/cordis.yml.

Contract layer (/api)

Wire messages form a four-quadrant discriminated union — who initiates × request/response — decoupled from the physical channel: ClientRequest (POST /api/<method> body), ServerResponse (that POST's response body), ServerRequest (SSE frame), ClientResponse (POST /api/respond body). Responses always echo the matching request's rpcId and never mint a new one. Method parameter/return structures live only in the domain interface signatures (SessionsApi, HostApi, EventsApi); RpcMethodMap registers the methods and every other position derives via RequestPayload<K>/ResponseValue<K>. Zod schemas anchor satisfies z.ZodType<Wire<T>> and parse at two levels: envelope first, business payload second, dispatched per method. Business errors ride RpcResult's error branch (RpcErrorDetailsMap closes the code set); HTTP status expresses only the carrier.

The layering/protocol decisions are recorded in the GUI layering and RPC protocol RFC; the browser-side consumption architecture in the web client architecture RFC.

The mux stream projects the latest log-backed title as a validated session/title control frame after each attached-session subscription baseline and immediately after the corresponding live raw title event. This projection does not add titles to session.list; cold sessions remain metadata-only there until opening or resuming attaches their logs.

Workspace and Session lists are separate reconnect baselines. workspace.create creates a unique name or adopts an existing directory, session.create accepts an optional preallocated Session id, and host/workspace-changed plus host/session-added carry committed increments in either arrival order. SessionSummary.blank and the host/session-added frame carry the derived zero-events bit: clients hide blank sessions and reuse them per workspace, flip blank on the first host/session-status(running:true), and treat session.list as the reconnect authority; cold summaries are never blank because lazy persistence keeps never-appended sessions out of list().

session.search is a bounded content-search projection over the sessions visible through session.list. The gateway asks the optional ctx.sessionQuery service for globally ranked current-surface user, assistant, and steering matches, consumes that stream until it has at most 20 visible session/snippet pairs plus one lookahead, and revalidates every hit against the list-derived authorization set before returning it. Provider pages start at 20 hits; when a first-page request rejects that limit, the gateway probes 10, 5, 2, then 1 and retains the learned size for continuation and stale-generation restarts. Returned snippets contain at most 240 Unicode code points; a malformed non-string provider snippet fails closed at the Host, and the response schema independently rejects an oversized snippet at each client boundary. Keeping the authorization set in Host memory avoids SQLite's variable ceiling for large valid corpora without weakening visibility or ranking.

A stale continuation discards every partial result, deduplication entry, and cursor from that provider attempt, then restarts at the first page against the original list-derived visibility snapshot without discarding the learned provider page size. Limit probes and stale retries share the same limit of at most 100 provider calls (and therefore at most 2,000 inspected hits); a page larger than its requested limit, a repeated continuation cursor, or a still-unexhausted stream at that call budget fails closed as an internal business error. The carrier request signal cancels persistence listing, cold-summary collection, and every search call, including a limit or stale rejection observed concurrently with cancellation. A deployment without the service, or any unrecovered index/query failure, also returns an internal business error so clients can retain metadata-only matches.

session.history pages on message boundaries, and its tail page (no beforeSeq) carries two session-level extras the page window cannot supply: the in-flight partial's chunk events, and todos — the latest todo/write whole-list projection over the full log. Older pages omit todos because the projection is session-level, not per-page; a tail response that omits it means the whole log holds no todo/write, so clients read the absent field as the empty plan rather than as unchanged state.

The command.* and skill.* domains expose the host command registry and skill catalog to clients. Every method addresses one session's agent by sessionId (a served session always has an Agent; command.* resumes cold sessions through the same path as session.*, while skill.list resolves the project root from the session header without touching the Agent registry). command.execute runs a slash-command line host-side and returns a detached result; the carrier's request signal cancels the running handler. host/commands-changed is the catalog invalidation frame: clients refetch command.list instead of diffing.

Carrier layer (/client + root)

AbstractApiClient holds every protocol invariant — rpcId minting, envelope wrap/unwrap, zod parsing, SSE frame decoding, unary timeout, microtask-batched envelope observation (subscribeEnvelopes) — while platform subclasses supply only the doFetch transport aspect. InProcessApiClient over toFetchHandler(api) is the isomorphic point: the full wire serialization/validation path with no network, used by dsh -p headless.

Model Experience

None, as the package defines the client↔host wire contract and carriers; nothing here reaches a model request.

KV Cache effect

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

Known Limitations and Deferred Work

• respond routing is shipped, but pending-interaction state is host-side work — the wire shape (POST /api/respond, RpcReceipt) is final; the pending table that makes late/duplicate answers meaningful lives in src/api-proxy.ts and is still minimal (questions only, no approvals).
• Reserved seams stay out of RpcMethodMap — session.fork, prompt.mode: 'inject', task.list, host.listModels, and a describe hostInstanceId are documented reservations; an unknown method fails loud at envelope parse rather than getting a not-implemented code.
• No protocol version field — client and host ship together; host.describe gains a version negotiation field only when an independently released client exists.