oh-my-pi/docs/sdk.md

# SDK

The SDK is the in-process integration surface for `@oh-my-pi/pi-coding-agent`.
Use it when you want direct access to agent state, event streaming, tool wiring, and session control from your own Bun/Node process.

If you need cross-language/process isolation, use RPC mode instead.

## Installation

```bash
bun add @oh-my-pi/pi-coding-agent
```

## Entry points

`@oh-my-pi/pi-coding-agent` exports the SDK APIs from the package root (and also via `@oh-my-pi/pi-coding-agent/sdk`).

Core exports for embedders:

- `createAgentSession`
- `SessionManager`
- `Settings`
- `AuthStorage`
- `ModelRegistry`
- `discoverAuthStorage`
- Discovery helpers (`discoverExtensions`, `discoverSkills`, `discoverContextFiles`, `discoverPromptTemplates`, `discoverSlashCommands`, `discoverCustomTSCommands`, `discoverMCPServers`)
- Tool factory surface (`createTools`, `BUILTIN_TOOLS`, tool classes)

## Quick start (auto-discovery defaults)

```ts
import { createAgentSession } from "@oh-my-pi/pi-coding-agent";

const { session, modelFallbackMessage } = await createAgentSession();

if (modelFallbackMessage) {
  process.stderr.write(`${modelFallbackMessage}\n`);
}

const unsubscribe = session.subscribe((event) => {
  if (
    event.type === "message_update" &&
    event.assistantMessageEvent.type === "text_delta"
  ) {
    process.stdout.write(event.assistantMessageEvent.delta);
  }
});

await session.prompt("Summarize this repository in 3 bullets.");
unsubscribe();
await session.dispose();
```

## What `createAgentSession()` discovers by default

`createAgentSession()` follows “provide to override, omit to discover”.

If omitted, it resolves:

- `cwd`: `getProjectDir()`
- `agentDir`: `~/.omp/agent` (via `getAgentDir()`)
- `authStorage`: `discoverAuthStorage(agentDir)`
- `modelRegistry`: `new ModelRegistry(authStorage)` + background `refreshInBackground()` when the registry is not provided
- `settings`: `await Settings.init({ cwd, agentDir })`
- `sessionManager`: `SessionManager.create(cwd)` (file-backed)
- skills/context files/prompt templates/slash commands/extensions/custom TS commands
- built-in tools via `createTools(...)`
- MCP tools (enabled by default; Exa MCP servers are folded into native Exa integration, and browser automation MCP servers are filtered when the built-in browser tool is enabled)
- LSP integration (enabled by default)
- `eventBus`: new `EventBus()` unless supplied

### Required vs optional inputs

Typically you must provide only what you want to control:

- **Must provide**: nothing for a minimal session
- **Usually provide explicitly** in embedders:
  - `sessionManager` (if you need in-memory or custom location)
  - `authStorage` + `modelRegistry` (if you own credential/model lifecycle)
  - `model` or `modelPattern` (if deterministic model selection matters)
  - `settings` (if you need isolated/test config)

## Session manager behavior (persistent vs in-memory)

`AgentSession` always uses a `SessionManager`; behavior depends on which factory you use.

### File-backed (default)

```ts
import { createAgentSession, SessionManager } from "@oh-my-pi/pi-coding-agent";

const { session } = await createAgentSession({
  sessionManager: SessionManager.create(process.cwd()),
});

console.log(session.sessionFile); // absolute .jsonl path
```

- Persists conversation/messages/state deltas to session files.
- Supports resume/open/list/fork workflows.
- `session.sessionFile` is defined.

### In-memory

```ts
import { createAgentSession, SessionManager } from "@oh-my-pi/pi-coding-agent";

const { session } = await createAgentSession({
  sessionManager: SessionManager.inMemory(),
});

console.log(session.sessionFile); // undefined
```

- No filesystem persistence.
- Useful for tests, ephemeral workers, request-scoped agents.
- Session methods still work, but persistence-specific behaviors (file resume/fork paths) are naturally limited.

### Resume/open/list helpers

```ts
import { SessionManager } from "@oh-my-pi/pi-coding-agent";

const recent = await SessionManager.continueRecent(process.cwd());
const listed = await SessionManager.list(process.cwd());
const opened = listed[0] ? await SessionManager.open(listed[0].path) : null;
```

## Model and auth wiring

`createAgentSession()` uses `ModelRegistry` + `AuthStorage` for model selection and API key resolution.

### Explicit wiring

```ts
import {
  createAgentSession,
  discoverAuthStorage,
  ModelRegistry,
  SessionManager,
} from "@oh-my-pi/pi-coding-agent";

const authStorage = await discoverAuthStorage();
const modelRegistry = new ModelRegistry(authStorage);
await modelRegistry.refresh();

const available = modelRegistry.getAvailable();
if (available.length === 0)
  throw new Error("No authenticated models available");

const { session } = await createAgentSession({
  authStorage,
  modelRegistry,
  model: available[0],
  thinkingLevel: "medium",
  sessionManager: SessionManager.inMemory(),
});
```

### Selection order when `model` is omitted

When no explicit `model`/`modelPattern` is provided:

1. restore model from existing session (if restorable + key available)
2. settings default model role (`default`)
3. first available model with valid auth

If restore fails, `modelFallbackMessage` explains fallback.

### Auth priority

`AuthStorage.getApiKey(...)` resolves in this order:

1. runtime override (`setRuntimeApiKey`, used by CLI `--api-key`)
2. config-sourced API key override (`models.yml` provider `apiKey`)
3. stored OAuth credential, including refresh when needed
4. API key persisted by a successful `/login`
5. provider environment variables
6. other stored API-key credential in `agent.db` / broker-backed storage
7. custom-provider resolver fallback

## Event subscription model

Subscribe with `session.subscribe(listener)`; it returns an unsubscribe function.

```ts
const unsubscribe = session.subscribe((event) => {
  switch (event.type) {
    case "agent_start":
    case "turn_start":
    case "tool_execution_start":
      break;
    case "message_update":
      if (event.assistantMessageEvent.type === "text_delta") {
        process.stdout.write(event.assistantMessageEvent.delta);
      }
      break;
  }
});
```

`AgentSessionEvent` includes core `AgentEvent` plus session-level events:

- `auto_compaction_start` / `auto_compaction_end`
- `auto_retry_start` / `auto_retry_end`
- `retry_fallback_applied` / `retry_fallback_succeeded`
- `ttsr_triggered`
- `todo_reminder` / `todo_auto_clear`
- `irc_message`

## Prompt lifecycle

`session.prompt(text, options?)` is the primary entry point.

Behavior:

1. optional command/template expansion (`/` commands, custom commands, file slash commands, prompt templates)
2. if currently streaming:
   - `streamingBehavior: "steer" | "followUp"` chooses how `prompt()` queues
   - extension `sendUserMessage(content)` defaults to steer when `deliverAs` is omitted
   - queued messages are preserved instead of throwing work away
3. if idle:
   - validates model + API key
   - appends user message
   - starts agent turn

Related APIs:

- `sendUserMessage(content, { deliverAs? })`
- `steer(text, images?)`
- `followUp(text, images?)`
- `sendCustomMessage({ customType, content, ... }, { deliverAs?, triggerTurn? })`
- `abort()`

## Tools and extension integration

### Built-ins and filtering

- Built-ins come from `createTools(...)` and `BUILTIN_TOOLS`.
- `toolNames` acts as an allowlist for built-ins.
- `customTools` and extension-registered tools are still included.
- Hidden tools (for example `yield`) are opt-in unless required by options.

```ts
const { session } = await createAgentSession({
  toolNames: ["read", "search", "find", "write"],
  requireYieldTool: true,
});
```

### Extensions

- `extensions`: inline `ExtensionFactory[]`
- `additionalExtensionPaths`: load extra extension files
- `disableExtensionDiscovery`: disable automatic extension scanning
- `preloadedExtensions`: reuse already loaded extension set

### Runtime tool set changes

`AgentSession` supports runtime activation updates:

- `getActiveToolNames()`
- `getAllToolNames()`
- `setActiveToolsByName(names)`
- `refreshMCPTools(mcpTools)`

System prompt is rebuilt to reflect active tool changes.

## Discovery helpers

Use these when you want partial control without recreating internal discovery logic:

- `discoverAuthStorage(agentDir?)`
- `discoverExtensions(cwd?)`
- `discoverSkills(cwd?, _agentDir?, settings?)`
- `discoverContextFiles(cwd?, _agentDir?)`
- `discoverPromptTemplates(cwd?, agentDir?)`
- `discoverSlashCommands(cwd?)`
- `discoverCustomTSCommands(cwd?, agentDir?)`
- `discoverMCPServers(cwd?)`
- `buildSystemPrompt(options?)`

## Subagent-oriented options

For SDK consumers building orchestrators (similar to task executor flow):

- `outputSchema`: passes structured output expectation into tool context
- `requireYieldTool`: forces `yield` tool inclusion
- `taskDepth`: recursion-depth context for nested task sessions
- `parentTaskPrefix`: artifact naming prefix for nested task outputs

These are optional for normal single-agent embedding.

## `createAgentSession()` return value

```ts
type CreateAgentSessionResult = {
  session: AgentSession;
  extensionsResult: LoadExtensionsResult;
  setToolUIContext: (uiContext: ExtensionUIContext, hasUI: boolean) => void;
  mcpManager?: MCPManager;
  modelFallbackMessage?: string;
  lspServers?: Array<{
    name: string;
    status: "connecting" | "ready" | "error" | "available";
    fileTypes: string[];
    error?: string;
  }>;
  eventBus: EventBus;
};
```

Use `setToolUIContext(...)` only if your embedder provides UI capabilities that tools/extensions should call into.

## Startup performance

`createAgentSession()` runs two background optimizations to overlap I/O with the rest of session setup:

- **Model-host preconnect.** As soon as the model is resolved, the SDK fires a best-effort `fetch.preconnect(model.baseUrl)` so DNS + TCP + TLS + HTTP/2 to the provider's host happens in parallel with extension/skill load, tool registry build, and system-prompt assembly. The first real `fetch(...)` then reuses the warm connection, saving 100–300 ms on transcontinental hops (e.g. residential IP → `api.anthropic.com`). Implementation lives in `preconnectModelHost()` in `packages/coding-agent/src/sdk.ts`. If `fetch.preconnect` is unavailable (non-Bun runtime) or the call throws, the optimization is silently skipped — never a hard dependency. Applies to every mode (interactive, print, RPC, ACP).
- **Conditional LSP warmup.** Startup LSP servers (those returned by `discoverStartupLspServers(cwd)`) are only warmed when **all** of these hold:
  - `enableLsp !== false` on the session options, **and**
  - `options.hasUI === true` (interactive TUI), **and**
  - the `lsp.lazy` setting is disabled (it defaults to `true`).

  With `lsp.lazy` enabled — the default — no language servers are launched at startup at all; each server cold-starts on first use, i.e. when the agent invokes the `lsp` tool or an edit/write touches a file whose extension matches the server's `fileTypes`. Print / script / RPC / ACP invocations (`hasUI=false`) skip the warmup regardless of the setting: they don't render the warmup status indicator and typically finish before the language servers would stabilize, so warming them just spends CPU parsing big `initialize` responses concurrently with the LLM stream consumer and jitters perceived latency. Tools that actually need an LSP server still spin one up on demand through `getOrCreateClient()` — only the _startup_ warmup is skipped. The returned `lspServers` field in `CreateAgentSessionResult` is still populated for UI sessions in lazy mode — recognized servers are discovered (no processes spawned) and reported with status `"available"` so the welcome screen and `/status` can list them; it is `undefined` only when `enableLsp === false` or `hasUI === false`.

## Minimal controlled embed example

```ts
import {
  createAgentSession,
  discoverAuthStorage,
  ModelRegistry,
  SessionManager,
  Settings,
} from "@oh-my-pi/pi-coding-agent";

const authStorage = await discoverAuthStorage();
const modelRegistry = new ModelRegistry(authStorage);
await modelRegistry.refresh();

const settings = Settings.isolated({
  "compaction.enabled": true,
  "retry.enabled": true,
});

const { session } = await createAgentSession({
  authStorage,
  modelRegistry,
  settings,
  sessionManager: SessionManager.inMemory(),
  toolNames: ["read", "search", "find", "edit", "write"],
  enableMCP: false,
  enableLsp: true,
});

session.subscribe((event) => {
  if (
    event.type === "message_update" &&
    event.assistantMessageEvent.type === "text_delta"
  ) {
    process.stdout.write(event.assistantMessageEvent.delta);
  }
});

await session.prompt("Find all TODO comments in this repo and propose fixes.");
await session.dispose();
```