deepseek-harness/packages/host/runtime

@deepseek-ai/dsh-host-runtime

Host runtime assembly for dsh: bootHost composes the core plugin spine (LLM service + DeepSeek adapter, sessions with JSONL persistence and immediate fallback titles, optional first-message model summaries, system prompt, tools, agents, agent loop, workspace instructions, local bash, and the provider-neutral user-interaction service), createApiProxy implements the dsh-host-apiproxy contract over that composition, and startHost is the one-step shell seam returning { api, handler, defaults, ctx, dispose }.

Which plugins mount and with what defaults is decided only here — shells must not ctx.plugin to alter the assembly. RunningHost.ctx is a formal seam with exactly two sanctioned uses: mounting protocol front-door plugins (e.g. a future dsh acp) and headless session-event subscription; consuming clients must not bypass api through it.

Configuration

Key	Default	Contract
persistenceRoot	(required)	Root directory for JSONL session persistence.
workspaceContext	(required)	AGENTS.md/CLAUDE.md loader config with an explicit maxBytes, or false to disable it.
provider	'deepseek'	Default provider route injected as agentOptions on create/resume and reported by host.describe.
model	'deepseek-v4-flash'	Default model id, same single source as provider.
cwd	process.cwd()	Default project directory for a session whose create request omits cwd.
sessionTitle	5 words / 40 fallback bytes / 80 accepted bytes	Deterministic fallback and accepted-title limits.
sessionTitleLlm	disabled	true enables the 5-word / 10-CJK-character, 4,096-input-byte, 64-output-token, 60-second first-message policy; an explicit config overrides it. An omitted route inherits the logged main-request provider and model.

ApiProxy implementation notes

Unary methods take the narrow RpcRequest<P> and echo request.rpcId; a prompt's rpcId rides MessageSource into the user/message event so clients can promote optimistic echoes. history/prompt on a cold session implicitly resume it, deduplicating concurrent calls through an in-flight table; history paginates backwards on message boundaries (never mid-message). The mux stream replays a session/subscribed baseline per attached session and every still-pending question with its original rpcId. Question responses, including blank per-item answers, are validated against the owning session and exact request before an atomic first-wins claim; answer, whole-request cancellation, owner abort, and provider disposal broadcast question/resolved. The host stream carries session lifecycle, running flips, and agent/error as the only outlet for live failures with no turn position.

Model Experience

Indirectly, through the non-blocking first-message title request owned by dsh-session-title-llm when sessionTitleLlm is enabled, the provider/model defaults injected into created and resumed agents, the other model-facing plugins bootHost mounts, and the logged workspace-instruction prefix when workspaceContext is enabled.

KV Cache effect

No main-request invalidation; when enabled, the auxiliary title request has its own cache behavior and leaves the conversation prefix unchanged.

Known Limitations and Deferred Work

• Question waits are process-memory state — browser reconnects recover them, but a host process restart aborts the owning tool call instead of restoring the wait from persistence.
• host.describe.version is a placeholder — it does not yet report the apps/cli package version.
• The assembly is fixed — per-deployment plugin selection (user profile, log sinks, alternative persistence) has a documented home here but no configuration surface yet.