wehub-resource-sync
68 lines
3.6 KiB
Plaintext
68 lines
3.6 KiB
Plaintext
---
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title: "Anatomy of an agent"
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sidebarTitle: "Anatomy"
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description: "The moving parts of a chat agent — the agent task, the session, the frontend transport — and which page covers each."
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---
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**A chat agent is three parts: a long-lived agent task that runs the turn loop, a durable Session carrying messages in and the response stream out, and a frontend transport that plugs the session into `useChat`.** The pages in this section each own one part of that picture. This page is the map — if you'd rather read mechanics end to end, skip to [How it works](/ai-chat/how-it-works).
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```mermaid
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flowchart LR
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FE["Frontend<br/>useChat + transport"] -- "user messages" --> IN([Session .in])
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IN --> AGENT["Agent task<br/>turn loop + hooks"]
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AGENT --> OUT([Session .out])
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OUT -- "streamed response" --> FE
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```
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Everything below maps onto one annotated agent:
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```ts trigger/my-agent.ts
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import { chat } from "@trigger.dev/sdk/ai";
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import { streamText, stepCountIs } from "ai";
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import { anthropic } from "@ai-sdk/anthropic";
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export const myAgent = chat.agent({
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id: "my-agent",
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// Tools declared on the config survive history re-conversion
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// across turns — see Tools.
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tools: { searchDocs },
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// Hooks fire around each turn: validation, persistence,
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// post-turn work — see Lifecycle hooks.
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onTurnComplete: async ({ responseMessage }) => {
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await db.messages.save(responseMessage);
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},
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// The turn loop. Messages arrive accumulated; you stream back.
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// Options, levels, and alternatives — see Backend.
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run: async ({ messages, tools, signal }) =>
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streamText({
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...chat.toStreamTextOptions({ tools }),
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model: anthropic("claude-sonnet-4-5"),
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messages,
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abortSignal: signal,
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stopWhen: stepCountIs(15),
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}),
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});
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```
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The frontend side is one hook — `useTriggerChatTransport` connects `useChat` to the agent's session, no API routes ([Frontend](/ai-chat/frontend)). Underneath, the conversation lives on a [Session](/ai-chat/sessions): a pair of durable streams keyed on your `chatId` that survives refreshes, deploys, and run boundaries.
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## Where each part is covered
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| Part | Page |
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| ----------------------------------------------------- | ---------------------------------------------- |
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| `chat.agent()` options, the turn loop, piping | [Backend](/ai-chat/backend) |
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| Hooks around each turn (`onTurnComplete`, hydration) | [Lifecycle hooks](/ai-chat/lifecycle-hooks) |
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| Declaring tools, typed payloads, `toModelOutput` | [Tools](/ai-chat/tools) |
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| `useChat` wiring, tokens, starting sessions | [Frontend](/ai-chat/frontend) |
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| Driving a chat from your server instead of a browser | [Server-side chat](/ai-chat/server-chat) |
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| The durable substrate under every agent | [Sessions](/ai-chat/sessions) |
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| Per-run typed state inside the loop | [chat.local](/ai-chat/chat-local) |
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| Type-safe payloads, client data, and messages | [Types](/ai-chat/types) |
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| Building without the managed lifecycle | [Custom agents](/ai-chat/custom-agents) |
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| End-to-end mechanics: what survives a refresh and why | [How it works](/ai-chat/how-it-works) |
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Beyond this section: [Features](/ai-chat/fast-starts) covers opt-in capabilities (Head Start, compaction, steering, actions), and [Patterns](/ai-chat/patterns/sub-agents) covers production recipes (sub-agents, HITL approvals, persistence, recovery).
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