feat(sdk): AI SDK custom useChat transport & chat.task harness

.changeset/ai-sdk-chat-transport.md

@@ -0,0 +1,42 @@
+---
+"@trigger.dev/sdk": minor
+---
+
+Add AI SDK chat transport integration via two new subpath exports:
+
+**`@trigger.dev/sdk/chat`** (frontend, browser-safe):
+- `TriggerChatTransport` — custom `ChatTransport` for the AI SDK's `useChat` hook that runs chat completions as durable Trigger.dev tasks
+- `createChatTransport()` — factory function
+
+```tsx
+import { useChat } from "@ai-sdk/react";
+import { TriggerChatTransport } from "@trigger.dev/sdk/chat";
+
+const { messages, sendMessage } = useChat({
+  transport: new TriggerChatTransport({
+    task: "my-chat-task",
+    accessToken,
+  }),
+});
+```
+
+**`@trigger.dev/sdk/ai`** (backend, extends existing `ai.tool`/`ai.currentToolOptions`):
+- `chatTask()` — pre-typed task wrapper with auto-pipe support
+- `pipeChat()` — pipe a `StreamTextResult` or stream to the frontend
+- `CHAT_STREAM_KEY` — the default stream key constant
+- `ChatTaskPayload` type
+
+```ts
+import { chatTask } from "@trigger.dev/sdk/ai";
+import { streamText, convertToModelMessages } from "ai";
+
+export const myChatTask = chatTask({
+  id: "my-chat-task",
+  run: async ({ messages }) => {
+    return streamText({
+      model: openai("gpt-4o"),
+      messages: convertToModelMessages(messages),
+    });
+  },
+});
+```

.claude/rules/package-installation.md

@@ -0,0 +1,22 @@
+---
+paths:
+  - "**/package.json"
+---
+
+# Installing Packages
+
+When adding a new dependency to any package.json in the monorepo:
+
+1. **Look up the latest version** on npm before adding:
+   ```bash
+   pnpm view <package-name> version
+   ```
+   If unsure which version to use (e.g. major version compatibility), confirm with the user.
+
+2. **Edit the package.json directly** — do NOT use `pnpm add` as it can cause issues in the monorepo. Add the dependency with the correct version range (typically `^x.y.z`).
+
+3. **Run `pnpm i` from the repo root** after editing to install and update the lockfile:
+   ```bash
+   pnpm i
+   ```
+   Always run from the repo root, not from the package directory.

CLAUDE.md

@@ -6,6 +6,8 @@ This file provides guidance to Claude Code when working with this repository. Su
 
 This is a pnpm 10.23.0 monorepo using Turborepo. Run commands from root with `pnpm run`.
 
+**Adding dependencies:** Edit `package.json` directly instead of using `pnpm add`, then run `pnpm i` from the repo root. See `.claude/rules/package-installation.md` for the full process.
+
 ```bash
 pnpm run docker              # Start Docker services (PostgreSQL, Redis, Electric)
 pnpm run db:migrate           # Run database migrations