fix(chat): preserve adapterName on deserialized toJSON and add standalone reviver docs

Author: dancer

.changeset/six-dolls-smash.md

@@ -0,0 +1,5 @@
+---
+"chat": minor
+---
+
+export standalone reviver for workflow-safe deserialization without adapter dependencies

apps/docs/content/docs/api/chat.mdx

@@ -475,3 +475,13 @@ Get a `JSON.parse` reviver that deserializes `Thread` and `Message` objects from
 const data = JSON.parse(payload, bot.reviver());
 await data.thread.post("Hello from workflow!");
 ```
+
+There is also a standalone `reviver` export that works without a `Chat` instance. This is useful in Vercel Workflow functions where importing the full Chat instance (with its adapter dependencies) is not possible:
+
+```typescript
+import { reviver } from "chat";
+
+const data = JSON.parse(payload, reviver) as { thread: Thread; message: Message };
+```
+
+The standalone reviver uses lazy adapter resolution - the adapter is looked up from the Chat singleton when first accessed. Call `chat.registerSingleton()` before using thread methods like `post()` (typically inside a `"use step"` function).

packages/chat/src/channel.ts

@@ -386,7 +386,7 @@ export class ChannelImpl<TState = Record<string, unknown>>
     return {
       _type: "chat:Channel",
       id: this.id,
-      adapterName: this.adapter.name,
+      adapterName: this._adapterName ?? this.adapter.name,
       isDM: this.isDM,
     };
   }

packages/chat/src/serialization.test.ts

@@ -1,5 +1,6 @@
 import { WORKFLOW_DESERIALIZE, WORKFLOW_SERIALIZE } from "@workflow/serde";
 import { afterEach, beforeEach, describe, expect, it } from "vitest";
+import { ChannelImpl, type SerializedChannel } from "./channel";
 import { Chat } from "./chat";
 import { clearChatSingleton } from "./chat-singleton";
 import { Message, type SerializedMessage } from "./message";
@@ -827,6 +828,43 @@ describe("Serialization", () => {
       expect(parsed.text).toBe("Direct usage");
       expect(parsed.metadata.dateSent).toBeInstanceOf(Date);
     });
+
+    it("should allow re-serialization of a revived Thread without singleton", () => {
+      const json: SerializedThread = {
+        _type: "chat:Thread",
+        id: "slack:C123:1234.5678",
+        channelId: "C123",
+        isDM: false,
+        adapterName: "slack",
+      };
+
+      clearChatSingleton();
+
+      const thread = ThreadImpl.fromJSON(json);
+      const reserialized = thread.toJSON();
+
+      expect(reserialized._type).toBe("chat:Thread");
+      expect(reserialized.adapterName).toBe("slack");
+      expect(reserialized.id).toBe("slack:C123:1234.5678");
+    });
+
+    it("should allow re-serialization of a revived Channel without singleton", () => {
+      const json: SerializedChannel = {
+        _type: "chat:Channel",
+        id: "C123",
+        isDM: false,
+        adapterName: "slack",
+      };
+
+      clearChatSingleton();
+
+      const channel = ChannelImpl.fromJSON(json);
+      const reserialized = channel.toJSON();
+
+      expect(reserialized._type).toBe("chat:Channel");
+      expect(reserialized.adapterName).toBe("slack");
+      expect(reserialized.id).toBe("C123");
+    });
   });
 
   describe("@workflow/serde integration", () => {

packages/chat/src/thread.ts

@@ -729,7 +729,7 @@ export class ThreadImpl<TState = Record<string, unknown>>
       channelId: this.channelId,
       currentMessage: this._currentMessage?.toJSON(),
       isDM: this.isDM,
-      adapterName: this.adapter.name,
+      adapterName: this._adapterName ?? this.adapter.name,
     };
   }