feat: add plan_update chunk for chat streaming

Author: zimeg

slack_sdk/models/messages/chunk.py

@@ -67,6 +67,29 @@ def __init__(
         self.text = text
 
 
+class PlanUpdateChunk(Chunk):
+    type = "plan_update"
+
+    @property
+    def attributes(self) -> Set[str]:  # type: ignore[override]
+        return super().attributes.union({"title"})
+
+    def __init__(
+        self,
+        *,
+        title: str,
+        **others: Dict,
+    ):
+        """An updated title of plans for task and tool calls.
+
+        https://docs.slack.dev/messaging/sending-and-scheduling-messages#text-streaming
+        """
+        super().__init__(type=self.type)
+        show_unknown_key_warning(self, others)
+
+        self.title = title
+
+
 class URLSource(JsonObject):
     type = "url"
 

tests/slack_sdk/models/test_chunks.py

@@ -1,6 +1,6 @@
 import unittest
 
-from slack_sdk.models.messages.chunk import MarkdownTextChunk, TaskUpdateChunk, URLSource
+from slack_sdk.models.messages.chunk import MarkdownTextChunk, PlanUpdateChunk, TaskUpdateChunk, URLSource
 
 
 class MarkdownTextChunkTests(unittest.TestCase):
@@ -14,6 +14,17 @@ def test_json(self):
         )
 
 
+class PlanUpdateChunkTests(unittest.TestCase):
+    def test_json(self):
+        self.assertDictEqual(
+            PlanUpdateChunk(title="Crunching numbers...").to_dict(),
+            {
+                "type": "plan_update",
+                "text": "Crunching numbers...",
+            },
+        )
+
+
 class TaskUpdateChunkTests(unittest.TestCase):
     def test_json(self):
         self.assertDictEqual(