# Runtime authoring

Use this page for routine scripts. Open the generated capability index only when a signature, default, support boundary, or installed-version fact is missing here.

## Script envelope

Start with the only legal export: `export const meta = { name, description, phases?: [{ title, detail?, model? }] }`. Values are nonblank literals; declare only used phases and call `phase()` before each phase's work. The remaining body already runs inside an async function: write helpers as ordinary declarations; `export default` and other exports are invalid. Return the result explicitly.

The runtime supplies `agent`, `parallel`, `pipeline`, `workflow`, quality/control helpers, `phase`, `log`, `args`, `cwd`, restricted `process.cwd()`, and `budget`. Imports, `require()`, filesystem modules, `Date.now()`, `Math.random()`, and no-argument `new Date()` are unavailable. The Node VM realm is implementation substrate, not a security boundary or public API.

## Topology

- `parallel()` takes thunks, runs independent work, and preserves input order. Await the whole array before whole-set synthesis.
- `pipeline()` runs stages sequentially per item while items proceed concurrently. Each stage receives `(previousValue, originalItem, index)` and forwards `null` to the next stage, so guard missing coverage first.
- `workflow(name, childArgs?)` runs a context-supplied saved workflow. Nesting is one level and shares limits, counters, tokens, and store.

## Data and failure

Call `agent(prompt, { label, executor?, schema?, required? })`; it returns text, a schema-validated value, or recoverable `null`. `executor` selects the complete harness: `pi` (default), `codex`, or `claude-code`. Use `required: true` for a critical agent whose exhausted recoverable failure must throw instead of becoming `null`; normal retries still run first, and the script may catch the thrown error intentionally. Nonrecoverable limit, validation, and budget failures throw. Record each intended work ID before filtering. A `null` means missing coverage, never a negative finding.

When JavaScript reads fields, pass a small plain JSON Schema. Schema noncompliance after repair throws and bypasses agent retries. Catch it only to return an explicit incomplete outcome without reading missing fields. Return objects, arrays, strings, numbers, booleans, and `null`—not functions, promises, cycles, `BigInt`, or runtime handles.

## Routing and support

Executor priority is call-site `executor` > run or manager default > `pi`; unknown values fail closed. Executor and model routing are independent: `model` never switches harnesses. Pi selector priority is explicit `model` > `agentType` model > `tier` > phase model > metadata model > implicit `medium` > session default. An unavailable selected Pi route falls directly to the session default. Use exact `model`, nonstandard `tier`, or `agentType` only when context supplies its name and purpose. Codex and Claude Code use ephemeral CLI sessions; same-ID resume and completed-run fork replay journaled results but restart live external calls. They retain cwd and role instructions but cannot use Pi SharedStore, `ToolDefinition`, or agent-type tool policies, so pass data through return values. Worktree isolation is best-effort. See [registry ownership](registry-ownership.md).

Generated entries marked `supported` are authoring API. `console` and whole-script Markdown fences are compatibility-only. VM realm facilities are internal. Active model routes and agent types are dynamic. Use `log()` in new scripts.