Cookbook: extension plugin shapes
Reference patterns for harness extensions. The snippets omit imports and helper implementations and are not copy-paste-complete. For concrete authoring paths, see the package checklist, first-tool tutorial, tool reference, and LLM adapter guide; the architecture owns the system and extension-point map.
A tool plugin
A tool registers on ctx.tools. The annotated defineTool example (typed execute arguments, result construction, the run_in_background pattern) lives in adding-a-tool.md — that guide is the source of truth for tool definitions. Raw JSON-Schema ToolDefinitions are also accepted by ctx.tools.register() directly (that is how MCP-sourced tools arrive); defineTool is the typed helper for first-party tools.
A hook plugin (permission-gate example)
This permission gate is one example of a hook plugin. It returns a typed decision from the tools/pre-execute gate to allow or deny a call; sandbox, permission, and plan-mode plugins can use this extension point. Hook plugins can intercept other extension points and are not inherently permission gates. A "native hook" is an ordinary Cordis plugin on an interception point; it needs no external protocol.
import type { Context } from '@deepseek-ai/cordis'
import type { PreToolDecision, ToolExecution } from '@deepseek-ai/dsh-tools'
declare function isAllowed(exec: ToolExecution): Promise<boolean>
export const name = 'permission-gate'
export function apply(ctx: Context) {
ctx.on('tools/pre-execute', async (exec, next): Promise<PreToolDecision> => {
if (!(await isAllowed(exec))) {
return { kind: 'deny', reason: 'Denied by policy.' }
}
return next()
})
}
This waterfall is the reorderable policy layer. Use ctx.tools.guard() when an invariant needs a monotonic final denial, tools/execute when a plugin must wrap the actual dispatch lifetime (timeouts/retries/metrics; only exec.signal is replaceable), tools/post-execute for explicit result transformation, and tools/result for contained observation of the immutable final outcome. The adding-a-tool guide gives the selection rule.
A UI plugin
A UI plugin renders from the session/event feed (the assistant token stream as assistant/chunk, plus turn/step boundaries and tool activity), and drives input back in via agent.followup() / agent.steer(). A browser plugin contributing a business row to the built-in Web Client instead registers a ConversationNodeDefinition and keyed Chat renderer; follow the Conversation Node guide.
import type { Context } from '@deepseek-ai/cordis'
import { createUserMessage } from '@deepseek-ai/dsh-llm'
import { SessionId } from '@deepseek-ai/dsh-session'
declare function render(text: string): void
declare function onUserInput(handler: (text: string) => void): void
export const name = 'my-ui'
export const inject = ['agents']
export function apply(ctx: Context) {
ctx.on('session/event', (_session, event) => {
if (event.type === 'assistant/chunk' && event.data.chunk.type === 'text-delta') {
render(event.data.chunk.text)
}
})
onUserInput(text => ctx.agents.get(SessionId('client-session'))?.followup(createUserMessage({
content: [{ type: 'text', text }],
source: { kind: 'user' },
})))
}
An external protocol driver
A protocol driver adapts a wire peer to ctx.agents; it may serve a UI or an automation client. A stdio driver owns stdout, creates or resumes agents through the factory, and maps protocol requests to followup() or cancel(). A low-level prompt request returns its durable enqueue receipt; it does not acquire a result by correlating MessageId with turn/end. Publish whole-agent status separately. An automation method may wait from its receipt through the next idle and summarize that explicitly owned interval, while a UI normally keeps observing the open-ended event stream. Tear agents down with AgentHandle.dispose() so disposal reaches quiescence.
packages/acp/acp is the automation-only worked example: it exposes fresh text sessions over Agent Client Protocol JSON-RPC stdio, emits committed assistant text, and registers a one-shot machine permission answerer for agents it owns. Its README defines the exact methods, event order, and lifecycle contract.
import type { Context } from '@deepseek-ai/cordis'
export const name = 'my-protocol-bridge'
export const inject = ['agents', 'sessions', 'sessionPersistence']
export function apply(ctx: Context) {
// Stream every logged assistant text/reasoning delta out to the client.
ctx.on('session/event', (_session, event) => {
if (event.type === 'assistant/chunk') {
const chunk = event.data.chunk
if (chunk.type === 'text-delta') {
// sendToClient({ kind: 'message_chunk', text: chunk.text })
}
}
})
// Inbound "prompt": create/resume an agent, feed it, and return its enqueue receipt.
// Whole-agent status is a separate notification; no turn end belongs to this prompt.
// Teardown reaches quiescence via AgentHandle.dispose() (stop + await exit).
}
Runnable wirings
Runnable leaves load their plugin trees from examples/*/cordis.yml; the root demo:* scripts and those leaf directories are the authoritative inventory. The product dsh launcher owns Web and one-shot headless execution, ACP leaves use @deepseek-ai/dsh-acp-demo, and JSON-RPC leaves use @deepseek-ai/dsh-sdk-jsonrpc-demo. The headless snapshot leaf mounts @deepseek-ai/dsh-agent-spine-demo and JSONL persistence explicitly, then drives them through an example-owned test fixture rather than a shipped app package.
The feature → mechanism map
Every product feature maps to a listener on a documented extension point — the microkernel claim made checkable (microkernel Agent Note). No row modifies the loop.
system-prompt/assemble is an expert cooperative whole-assembly transform: its returned assembly is authoritative, so listener authors own preserving active Code Mode and structured-output protocol contributions. Prefer ctx.tools.restrict() for tool filtering that must stay aligned across presentation, lookup, and execution.
| Product feature | Plugin mechanism |
|---|---|
| Hook system (user + project level) | listeners on agent/session-start, agent/pre-step, agent/request, tools/pre-execute, tools/post-execute, and agent/turn-stopping; the waterfalls return typed decisions, while agent/turn-stopping may steer another step; the dsh-hooks-claude-code / dsh-hooks-codex bridges map hook config files onto these extension points |
/goal |
ctx.goals owns durable state, dsh-goal-round-driver schedules same-session rounds through the public Agent, and separate command/tool producers expose human/model control |
/loop |
on the turn/end session event, followup() the next iteration; or force-continue |
| Dynamic workflow | ctx.workflowEngine + the worker-thread engine + the workflow tool; structured in-process children enforce output with scoped prompt/tool registrations, a monotonic tool guard, final tools/result commit (including enclosing run_code), and the structured-output execution's monotonic concludeTurn() marker |
| Queued + steering messages | core Agent.followup() / Agent.steer() |
| Context compaction (auto + manual) | the ctx.compaction seam + dsh-compaction-basic; automatic pressure runs on serial agent/pre-step, canonical overflow recovery runs on agent/request-error, and manual callers use the same compact service (compaction Agent Note) |
| System prompt configurability | ctx.systemPrompt.section() with ordering and scope-local shadowing |
| AGENTS.md (root) | a section provider reading the file |
| AGENTS.md (subdir, on-touch) + file-change notices | agent.inject() from a watcher / tool-result listener |
| Built-in tools | ctx.tools.register(); schemas flow into the assembly automatically — the dsh-tool-* families (bash, fs, web, subagent, todo) are the shipped examples |
| ToolSearch / progressive disclosure | replace a scoped ctx.tools.restrict() registration as the visible set changes; the registry keeps presentation, lookup, and execution aligned |
| Tool deadline / retry / metrics | wrap core dispatch with tools/execute; a wrapper may replace exec.signal, delegate, and inspect the normalized result in one lexical lifetime |
| Final tool-result metrics / audit / capture | observe immutable authoritative outcomes with tools/result; use tools/post-execute instead only when the plugin must transform the result or attach context |
| Monotonic terminal turn policy | call ToolExecution.concludeTurn() from the successful terminal tool; later tool calls in the same response remain guardable, and the loop stops after the step |
| Subprocess sandbox (landlock / sandbox-exec) | use a ctx.sandbox backend through dsh-bash-sandbox; use tools/pre-execute for capability-level denial |
| Permission system / AskUserQuestion | return ask from tools/pre-execute and answer through ctx.approval; register a separate model-facing ask tool for ordinary user questions |
| Plan mode | @deepseek-ai/dsh-plan-mode — logged plan/mode state, the plan:policy guidance section, /plan [message] entry, /plan off direct exit, and the user-reviewed exit_plan_mode exit; enforcement stays on the independent sandbox/approval axes |
| Sub-agent delegation | the ctx.subagents provider registry (dsh-subagent-spawn-in-process/-fork/-acp/-codex/-claude-code/-dsh-sdk) + dsh-tool-subagent exposing one configured provider to the model |
| MCP | one plugin per server: discover tools → ctx.tools.register() |
| Skills | section + tool registration; inject() skill content on invocation |
| Memory | section provider + tool |
| Scheduled tasks (cron) | a plugin registers model-callable scheduling tools; timer fires → followup(…, {source: {kind: 'cron', …}}) when idle / inject() notification when busy |
| UI (GUI; CLI emits JSONL) | listen session/event (assistant chunks, boundaries, tool activity); input → followup() |
| Web Client Chat business node | register a ConversationNodeDefinition and conversation.chat.node keyed renderer |
| SessionTelemetryBackend / replayable trace | session/event → JSONL; replay = sessions.create(id, { seed }) |
| Model adapters | LlmAdapter subclass via registerAdapter (dsh-llm-deepseek, dsh-llm-pi-ai) |
| Plugin hot-reload | every registration is a ctx.effect → vendored HMR just works |