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2026-02-27· A3S Laba3s-codecoding-agentembeddabletypescriptsdk

A3S Code v2.1.0: The Coding Agent Runtime

A3S Code is an embeddable runtime for coding-agent workflows. A host application creates an agent, opens a workspace-bound session, and drives work through prompts, tools, deterministic programs, delegated tasks, replay, and verification evidence.

import { Agent } from '@a3s-lab/code';

const agent = await Agent.create('agent.acl');
const session = agent.session(process.cwd(), {
  builtinSkills: true,
  planningMode: 'enabled',
});

const result = await session.send(
  'Find where authentication errors are handled and summarize the flow.',
);

console.log(result.text);
console.log(result.verificationSummaryText);

Runtime Surface

  • ACL configuration with providers and models blocks.
  • OpenAI-compatible apiKey/baseUrl and api_key/base_url aliases.
  • Session options for model override, builtin skills, prompt slots, planning, file-backed memory/session stores, auto-save, compaction, continuation, and permission-policy shape.
  • Direct tools: read, glob, grep, bash, git, generic tool, skill search, and tool registry inspection.
  • Programmatic Tool Calling through session.program() and the core program tool.
  • Task delegation with delegateTask and parallelTask.
  • Run replay, trace events, verification summaries, and run-scoped inspection.
  • Live stdio MCP registration and tool invocation.
  • Queue inspection and external-task primitives.
  • Session persistence through save() and agent.resumeSession().

Streaming

Use .next() to consume the stream:

const stream = await session.stream('Explain the release risk in one paragraph.');

while (true) {
  const { value: event, done } = await stream.next();
  if (done) break;
  if (event?.text) process.stdout.write(event.text);
}

Use the streaming shape documented for your installed SDK version.

Why the Coding Agent Is Still the Core

Coding agents are valuable because they can close the loop with objective feedback: read code, make a change, run a command, inspect failure, and try again. A3S Code v2.1.0 exposes that loop as an embeddable runtime: sessions, tools, PTC, delegation, memory, replay, and verification evidence.

For the complete API surface covered by integration tests, see API Contract.

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