> ## Documentation Index
> Fetch the complete documentation index at: https://docs.terminaluse.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Building Agents

> The public Python runtime model for Terminal Use agents

You build Terminal Use agents with the Python runtime API.

The public runtime surface is `AgentServer`, and it exposes three lifecycle hooks:

* `@server.on_create`
* `@server.on_event`
* `@server.on_cancel`

There is no public `on_complete` hook.

## Start With tu init

```bash theme={"dark"}
tu init
```

That creates an agent project with:

```text theme={"dark"}
my-agent/
├── src/agent.py
├── config.yaml
├── Dockerfile
└── pyproject.toml
```

## Minimal Agent

```python theme={"dark"}
from typing import Any

from terminaluse.lib import AgentServer, TaskContext
from terminaluse.types import Event, TextPart

server = AgentServer()


@server.on_create
async def handle_create(ctx: TaskContext, params: dict[str, Any]):
    await ctx.state.create({"turns": 0})
    await ctx.messages.send("Task created.")


@server.on_event
async def handle_event(ctx: TaskContext, event: Event):
    if not isinstance(event.content, TextPart):
        await ctx.messages.send("Only text events are supported.")
        return

    state = await ctx.state.get() or {"turns": 0}
    turns = int(state.get("turns", 0)) + 1
    await ctx.state.update({"turns": turns})
    await ctx.messages.send(f"turn {turns}: {event.content.text}")


@server.on_cancel
async def handle_cancel(ctx: TaskContext):
    await ctx.messages.send("Task cancelled.")
```

## The Handler Model

### on\_create

Runs once when the task is created.

Use it for:

* initializing state
* validating params
* sending the first message

### on\_event

Runs every time your app sends an event to the task.

This is where most agent logic lives.

### on\_cancel

Runs when the task is cancelled.

Use it for cleanup or last-message behavior if needed.

Important runtime detail: `on_cancel` does not run with the normal automatic filesystem sync wrapper. Do not rely on `/workspace` writes made in `on_cancel` being persisted automatically.

## TaskContext

Every handler receives a `TaskContext`.

| Attribute      | Purpose                        |
| -------------- | ------------------------------ |
| `ctx.task`     | Current task metadata          |
| `ctx.agent`    | Current agent metadata         |
| `ctx.messages` | Send or list task messages     |
| `ctx.state`    | Read and update per-task state |
| `ctx.events`   | Send or list events            |

`TaskContext` is the default path. The lower-level `adk.*` modules are still useful in helper code when you need to pass IDs explicitly.

## Messages

The most common thing you do inside a handler is emit messages:

```python theme={"dark"}
await ctx.messages.send("plain text works")
```

For structured output, send a typed part:

```python theme={"dark"}
from terminaluse.types import DataPart

await ctx.messages.send(DataPart(data={"status": "complete"}))
```

## State

State is persisted per task and agent.

```python theme={"dark"}
await ctx.state.create({"status": "started"})

state = await ctx.state.get() or {}

await ctx.state.update({"status": "done"})
```

Use it for:

* conversation continuity
* IDs or handles you need on future turns
* lightweight workflow progress

## Filesystem Access

If the task has an attached filesystem, your agent sees it at `/workspace`.

Terminal Use syncs that filesystem around `on_create` and `on_event`. If the caller only has read access to the filesystem, `/workspace` is mounted read-only for that task.

`on_cancel` is the exception: the runtime skips the automatic sync wrapper for cancel handlers.

See [Filesystem Sync](/advanced/filesystem-sync) and [Access Control](/concepts/access-control).

## TypeScript vs Python

The TypeScript SDK is for calling deployed agents and managing Terminal Use resources from your application.

The public agent runtime shown on this page is Python.

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