## Summary
`chat.agent` now takes a `tools` option. Until now tools only went to
`streamText` inside `run()`, so the SDK had no tools when it
re-converted the persisted `UIMessage` history at the start of each
turn. Any tool with a `toModelOutput` (raw image bytes into an image
content part, or a sub-agent transcript compressed to a summary) had its
transform applied on turn 1 and skipped from turn 2 onward, so the raw
output got JSON-stringified back into the prompt and the model lost the
transformed view.
Declaring `tools` on the config threads them into that conversion, so
`toModelOutput` runs on every turn. The resolved set is handed back,
typed, on the `run()` payload as `tools`:
```ts
const tools = { searchDocs, renderChart };
export const myChat = chat.agent({
tools,
run: async ({ messages, tools, signal }) =>
streamText({ ...chat.toStreamTextOptions({ tools }), messages, abortSignal: signal }),
});
```
`tools` also accepts a per-turn function for tools that depend on the
user or a feature flag. Only `inputSchema` and `toModelOutput` are read
during conversion, never `execute`. Also exports
`InferChatUIMessageFromTools<typeof tools>` to derive the chat
`UIMessage` type from a tool set. No behavior change for agents that
don't declare `tools`.
Eric Allam
e9e2ec1cfc