feat: add BlockChunk type to chat.{start,append,stop}Stream methods

Author: srtaalej

packages/types/src/chunk.ts

@@ -1,4 +1,5 @@
 import type { URLSourceElement } from './block-kit/block-elements';
+import type { AnyBlock } from './block-kit/blocks';
 /**
  * Base interface for streaming message chunks.
  * https://docs.slack.dev/messaging/sending-and-scheduling-messages#text-streaming
@@ -39,7 +40,17 @@ export interface TaskUpdateChunk extends Chunk {
   sources?: URLSourceElement[];
 }
 
+/**
+ * Used for passing an array of blocks within a streaming message.
+ * https://docs.slack.dev/changelog/2026/04/16/block-kit-new-blocks/
+ */
+export interface BlocksChunk extends Chunk {
+  type: 'blocks';
+  /** @description An array of {@link AnyBlock} objects. Maximum of 50 blocks. */
+  blocks: AnyBlock[];
+}
+
 /**
  * Union type of all possible chunk types
  */
-export type AnyChunk = MarkdownTextChunk | PlanUpdateChunk | TaskUpdateChunk;
+export type AnyChunk = MarkdownTextChunk | PlanUpdateChunk | TaskUpdateChunk | BlocksChunk;

packages/types/test/chunk.test-d.ts

@@ -0,0 +1,35 @@
+import { expectAssignable, expectError } from 'tsd';
+import type { AnyChunk, BlocksChunk } from '../src/index';
+
+// BlocksChunk
+// -- sad path
+expectError<BlocksChunk>({});
+expectError<BlocksChunk>({ type: 'blocks' });
+expectError<BlocksChunk>({ blocks: [] });
+
+// -- happy path
+expectAssignable<BlocksChunk>({ type: 'blocks', blocks: [] });
+expectAssignable<BlocksChunk>({
+  type: 'blocks',
+  blocks: [
+    {
+      type: 'section',
+      text: { type: 'plain_text', text: "Sandra's plan outline" },
+    },
+  ],
+});
+expectAssignable<BlocksChunk>({
+  type: 'blocks',
+  blocks: [
+    { type: 'divider' },
+    { type: 'header', text: { type: 'plain_text', text: 'Hello' } },
+  ],
+});
+// Unknown block types accepted via generic Block interface
+expectAssignable<BlocksChunk>({
+  type: 'blocks',
+  blocks: [{ type: 'future_block_type' }],
+});
+
+// BlocksChunk is assignable to AnyChunk
+expectAssignable<AnyChunk>({ type: 'blocks', blocks: [] });