@tanstack/ai/dist/esm/activities/chat/middleware/pending-turn.js

Type-safe TypeScript AI SDK for streaming chat, tool calling, agents, structured outputs, and multimodal generation.

import { createCapability } from "./capabilities.js";
//#region src/activities/chat/middleware/pending-turn.ts
/**
* Internal seam that lets a SLOW middleware ask the persistence layer to store
* the user's pending turn NOW, before that middleware starts its slow work.
*
* WHY THIS EXISTS. Chat persistence stores the pending turn from `onStart`, which
* is the earliest hook that holds the merged message list. `onStart` runs after
* EVERY middleware `setup`, and that is normally a few milliseconds. `withSandbox`
* breaks the assumption: its `setup` creates a sandbox and clones a repository,
* which takes minutes. For that whole window the thread holds nothing, so a reload
* — or a second device — asks the server for the conversation and is told it is
* empty. The user sees no sign of the message they just sent.
*
* The provider owns the rule for WHAT to store. A caller must not rebuild that
* rule: `saveThread` replaces the whole thread, so a caller that stored only the
* newly-sent message would delete the history. Asking the owner to store the turn
* keeps the merge in one place.
*
* OPT-IN, so nothing changes for a fast run. Persistence offers this seam on every
* durable run; only a middleware that is about to be slow calls it. A run with no
* such middleware never calls it, and the `onStart` store stays the only one.
*
* A SEAM RATHER THAN A NEW MIDDLEWARE HOOK, deliberately. A lifecycle hook that
* runs before `setup` would be public API, and it would have to explain itself to
* every middleware author. This concern has one provider (`withPersistence`) and
* one caller (`withSandbox`), and it reaches across packages through the same
* internal channel the sandbox layer already uses for its runtime.
*/
var PendingTurnCapability = createCapability()("pending-turn");
var [getPendingTurn, providePendingTurn] = PendingTurnCapability;
//#endregion
export { PendingTurnCapability, getPendingTurn, providePendingTurn };

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