Matt Aitken
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## Summary When a `chat.agent` (or `chat.createSession`) turn's model stream fails mid-response (e.g. a transport timeout like `UND_ERR_BODY_TIMEOUT`), the assistant output that already streamed was dropped: `onTurnComplete` fired with `responseMessage: undefined`, and the manual loop's `turn.complete()` rethrew without keeping the partial. Apps that register `hydrateMessages` are hit hardest, since boot-time tail-replay recovery is off by design. This preserves the streamed-so-far assistant output while still reporting the turn as errored, so persistence and recovery keep it. ## Scope of behavior change Only the **error path** changes. Successful turns are unaffected: the same chunks stream to the client in the same order, and backpressure/cancel behave as before. Everything here is a correctness improvement on a turn that hit a source-stream failure. ## What it does Follow-up to #4304 (`chat.pipeAndCapture`), extending the same partial-recovery to the two loops that lacked it: - **`chat.agent`**: taps the response stream (via a `TransformStream`, so pass-through backpressure and cancel are preserved) to buffer chunks, and on a source-stream failure reconstructs the partial (preferring the `onFinish` message). It's surfaced on the error-path `onTurnComplete` (`responseMessage`, `rawResponseMessage`, `uiMessages`, `newUIMessages`, `newMessages`) and committed to the accumulator so the next turn and the reboot snapshot keep it. - **`chat.createSession` / `turn.complete()`**: the reconstructed partial is accumulated (so `turn.uiMessages` reflects it and the caller can persist after catching) before `turn.complete()` rethrows. `onBeforeTurnComplete` stays skipped on the error path (it hands out a writer for a stream that has already broken). ## Correctness properties (each covered by a regression test) Each test below was confirmed to fail without its fix: - The recovered partial reaches `onTurnComplete` and the next turn's accumulated messages. - An already-committed (possibly enriched) response is not overwritten if a post-response hook then throws. - Incomplete tool parts are cleaned from the recovered partial (text kept), so the UI and model views agree and the next turn isn't poisoned. - A prior turn's model-only compaction survives an errored turn (append only the new tail, don't reconvert the full history). - A reconstructed fragment that reuses an existing message id does not clobber the complete message. - Queued `chat.response` data parts are folded into the recovered partial, matching the success path. - `newMessages` (model delta) stays symmetric with `newUIMessages`. ## Tests New `chat-agent-source-stream-error.test.ts` covers the cases above. The full `@trigger.dev/sdk` unit suite passes and the package build is green across all supported runtimes (Node 20 to 26, Bun, Deno, Cloudflare Workers).
Official TypeScript SDK for Trigger.dev
The Trigger.dev SDK is a TypeScript/JavaScript library that allows you to define and trigger tasks in your projects.
About Trigger.dev
Trigger.dev is an open source platform for building and deploying fully-managed AI agents and workflows. Write workflows in normal async TypeScript for everything from simple tasks to long-running AI agents, heavy media processing, complex real-time systems and more. Complete with full observability, managed queues, and elastic infrastructure which handles the horizontal scaling.
Core features
- Task creation and execution
- CLI for development and deployment
- Build system with extensions
- Management API for runs, schedules, and environment variables
Key Components:
- Tasks: Background jobs written in TypeScript/JavaScript
- CLI: Commands for login, init, dev, deploy
- Build Extensions: Customize builds (Prisma, Python, FFmpeg, etc.)
- Management API: Programmatic control over runs and resources
Getting started
There are two ways to get started:
- Create an account in our web app, create a new project and follow the instructions in the onboarding. Build and deploy your first task in minutes.
- Manual setup in your existing project.
SDK documentation
For more information on our SDK, refer to our docs.
Support
If you have any questions, please reach out to us on Discord and we'll be happy to help.