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

.changeset/agent-skills.md

@@ -0,0 +1,16 @@
+---
+"@trigger.dev/sdk": patch
+"@trigger.dev/core": patch
+"@trigger.dev/build": patch
+"trigger.dev": patch
+---
+
+Add Agent Skills for `chat.agent`. Drop a folder with a `SKILL.md` and any helper scripts/references next to your task code, register it with `skills.define({ id, path })`, and the CLI bundles it into the deploy image automatically — no `trigger.config.ts` changes. The agent gets a one-line summary in its system prompt and discovers full instructions on demand via `loadSkill`, with `bash` and `readFile` tools scoped per-skill (path-traversal guards, output caps, abort-signal propagation).
+
+```ts
+const pdfSkill = skills.define({ id: "pdf-extract", path: "./skills/pdf-extract" });
+
+chat.skills.set([await pdfSkill.local()]);
+```
+
+Built on the [AI SDK cookbook pattern](https://ai-sdk.dev/cookbook/guides/agent-skills) — portable across providers. SDK + CLI only for now; dashboard-editable `SKILL.md` text is on the roadmap.

.changeset/ai-tool-helpers.md

@@ -0,0 +1,15 @@
+---
+"@trigger.dev/sdk": patch
+---
+
+Add `ai.toolExecute(task)` so you can wire a Trigger subtask in as the `execute` handler of an AI SDK `tool()` while defining `description` and `inputSchema` yourself — useful when you want full control over the tool surface and just need Trigger's subtask machinery for the body.
+
+```ts
+const myTool = tool({
+  description: "...",
+  inputSchema: z.object({ ... }),
+  execute: ai.toolExecute(mySubtask),
+});
+```
+
+`ai.tool(task)` (`toolFromTask`) keeps doing the all-in-one wrap and now aligns its return type with AI SDK's `ToolSet`. Minimum `ai` peer raised to `^6.0.116` to avoid cross-version `ToolSet` mismatches in monorepos.

.changeset/chat-agent.md

@@ -0,0 +1,30 @@
+---
+"@trigger.dev/sdk": minor
+"@trigger.dev/core": patch
+---
+
+Run AI chats as durable Trigger.dev tasks. Define the agent in one function, wire `useChat` to it from React, and the conversation survives page refreshes, network blips, and process restarts — with built-in support for tools, HITL approvals, multi-turn state, and stop-mid-stream cancellation.
+
+```ts
+import { chat } from "@trigger.dev/sdk/ai";
+import { streamText } from "ai";
+import { openai } from "@ai-sdk/openai";
+
+export const myChat = chat.agent({
+  id: "my-chat",
+  run: async ({ messages, signal }) =>
+    streamText({ model: openai("gpt-4o"), messages, abortSignal: signal }),
+});
+```
+
+```tsx
+import { useChat } from "@ai-sdk/react";
+import { useTriggerChatTransport } from "@trigger.dev/sdk/chat/react";
+
+const transport = useTriggerChatTransport({ task: "my-chat", accessToken });
+const { messages, sendMessage } = useChat({ transport });
+```
+
+Lifecycle hooks (`onPreload`, `onTurnStart`, `onTurnComplete`, etc.) cover the common needs around persistence, validation, and post-turn work. `chat.store` gives you a typed shared-data slot the agent and client both read and write. `chat.endRun()` exits cleanly when the agent decides it's done. The transport's `watch` mode lets a dashboard tab observe a run without driving it.
+
+Drops the pre-Sessions chat stream constants (`CHAT_STREAM_KEY`, `CHAT_MESSAGES_STREAM_ID`, `CHAT_STOP_STREAM_ID`) — migrate to `sessions.open(id).out` / `.in`.

.changeset/mcp-agent-chat-sessions.md

@@ -0,0 +1,5 @@
+---
+"trigger.dev": patch
+---
+
+The CLI MCP server's agent-chat tools (`start_agent_chat`, `send_agent_message`, `close_agent_chat`) now run on the new Sessions primitive, so AI assistants driving a `chat.agent` get the same idempotent-by-`chatId`, durable-across-runs behavior the browser transport gets. Required PAT scopes go from `write:inputStreams` to `read:sessions` + `write:sessions`.

.changeset/mock-chat-agent-test-harness.md

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+---
+"@trigger.dev/sdk": patch
+"@trigger.dev/core": patch
+---
+
+Unit-test `chat.agent` definitions offline with `mockChatAgent` from `@trigger.dev/sdk/ai/test`. Drives a real agent's turn loop in-process — no network, no task runtime — so you can send messages, actions, and stop signals via driver methods, inspect captured output chunks, and verify hooks fire. Pairs with `MockLanguageModelV3` from `ai/test` for model mocking. `setupLocals` lets you pre-seed `locals` (DB clients, service stubs) before `run()` starts.
+
+The broader `runInMockTaskContext` harness it's built on lives at `@trigger.dev/core/v3/test` — useful for unit-testing any task code, not just chat.

.changeset/sessions-primitive.md

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+---
+"@trigger.dev/core": patch
+"@trigger.dev/sdk": patch
+---
+
+Add Sessions — a durable, task-bound, bidirectional channel pair that outlives any single run. One identifier (your `externalId`), many runs over time, with a stable `.in` channel clients can write to and a stable `.out` channel they can subscribe to. Powers `chat.agent` (separate changeset), and unblocks anything that needs "resume tomorrow" or "approval loop" workflows.
+
+```ts
+const session = await sessions.create({ externalId: chatId, taskIdentifier: "my-task" });
+await session.in.send({ kind: "message", payload: "..." });
+for await (const chunk of session.out.read()) { /* ... */ }
+```
+
+Inside the task, `.in.wait()` / `.waitWithIdleTimeout()` suspends the run on a session-stream waitpoint until the next record arrives. `.out.append` / `.pipe` / `.writer` produce records via direct-to-S2 writes.