feat: add ThinkingChunk to StreamChunk protocol

src/chat_sdk/__init__.py

@@ -158,6 +158,7 @@
     StreamChunk,
     StreamOptions,
     TaskUpdateChunk,
+    ThinkingChunk,
     Thread,
     ThreadInfo,
     ThreadSummary,
@@ -339,6 +340,7 @@
     "StreamChunk",
     "StreamOptions",
     "TaskUpdateChunk",
+    "ThinkingChunk",
     "Thread",
     "ThreadInfo",
     "ThreadSummary",

src/chat_sdk/adapters/slack/adapter.py

@@ -2057,6 +2057,8 @@ async def send_structured_chunk(chunk: StreamChunk) -> None:
                     chunk_data["output"] = chunk.output  # type: ignore[union-attr]
                 if hasattr(chunk, "text"):
                     chunk_data["text"] = chunk.text  # type: ignore[union-attr]
+                if hasattr(chunk, "content"):
+                    chunk_data["content"] = chunk.content  # type: ignore[union-attr]
 
                 if first:
                     await streamer.append(chunks=[chunk_data], token=token)

src/chat_sdk/adapters/teams/adapter.py

@@ -785,20 +785,35 @@ async def stream(
         accumulated = ""
         message_id: str | None = None
 
+        thinking = ""
+
         async for chunk in text_stream:
             text = ""
             if isinstance(chunk, str):
                 text = chunk
             elif isinstance(chunk, dict) and chunk.get("type") == "markdown_text":
                 text = chunk.get("text", "")
+            elif hasattr(chunk, "type"):
+                chunk_type = getattr(chunk, "type", None)
+                if chunk_type == "markdown_text":
+                    text = getattr(chunk, "text", "")
+                elif chunk_type == "thinking":
+                    thinking = getattr(chunk, "content", "")
+                    # Render thinking as italic context above the main text
+                    if accumulated or not message_id:
+                        continue  # Will be included in next text update
             if not text:
                 continue
 
             accumulated += text
 
+            display_text = accumulated
+            if thinking:
+                display_text = f"*{thinking}*\n\n{accumulated}"
+
             activity_payload = {
                 "type": "message",
-                "text": accumulated,
+                "text": display_text,
                 "textFormat": "markdown",
             }
 

src/chat_sdk/types.py

@@ -740,6 +740,19 @@ class TaskUpdateChunk:
     output: str | None = None
 
 
+@dataclass
+class ThinkingChunk:
+    """AI reasoning/thinking display.
+
+    Used by agents that emit structured thinking events (e.g. pydantic-ai
+    ``ThinkingPart``).  Adapters can render these as context blocks (Slack),
+    Adaptive Card sections (Teams), or styled text on other platforms.
+    """
+
+    type: Literal["thinking"] = "thinking"
+    content: str = ""
+
+
 @dataclass
 class PlanUpdateChunk:
     """Plan title update."""
@@ -748,7 +761,7 @@ class PlanUpdateChunk:
     title: str = ""
 
 
-StreamChunk = MarkdownTextChunk | TaskUpdateChunk | PlanUpdateChunk
+StreamChunk = MarkdownTextChunk | TaskUpdateChunk | ThinkingChunk | PlanUpdateChunk
 
 
 @dataclass

tests/test_teams_coverage.py

@@ -1085,6 +1085,53 @@ async def text_stream():
         result = await adapter.stream(tid, text_stream())
         assert result.id == ""  # nothing sent
 
+    async def test_stream_thinking_chunk_renders_italic(self):
+        adapter = _make_adapter(logger=_make_logger())
+        update_mock = AsyncMock()
+        adapter._teams_send = AsyncMock(return_value={"id": "s1"})
+        adapter._teams_update = update_mock
+
+        tid = adapter.encode_thread_id(
+            TeamsThreadId(
+                conversation_id="19:abc@thread.tacv2",
+                service_url="https://smba.trafficmanager.net/teams/",
+            )
+        )
+
+        from chat_sdk.types import ThinkingChunk
+
+        async def text_stream():
+            yield ThinkingChunk(content="Analyzing request")
+            yield "Hello "
+            yield "World"
+
+        result = await adapter.stream(tid, text_stream())
+        assert result.raw["text"] == "Hello World"
+        # The update call should have included the italic thinking prefix
+        last_update_payload = update_mock.call_args_list[-1][0][2]
+        assert "*Analyzing request*" in last_update_payload["text"]
+
+    async def test_stream_thinking_chunk_without_text_is_skipped(self):
+        adapter = _make_adapter(logger=_make_logger())
+        adapter._teams_send = AsyncMock(return_value={"id": "s1"})
+        adapter._teams_update = AsyncMock()
+
+        tid = adapter.encode_thread_id(
+            TeamsThreadId(
+                conversation_id="19:abc@thread.tacv2",
+                service_url="https://smba.trafficmanager.net/teams/",
+            )
+        )
+
+        from chat_sdk.types import ThinkingChunk
+
+        async def text_stream():
+            yield ThinkingChunk(content="Just thinking...")
+
+        result = await adapter.stream(tid, text_stream())
+        # No text was yielded so nothing should have been sent
+        assert result.raw["text"] == ""
+
 
 # ---------------------------------------------------------------------------
 # _extract_card_title

tests/test_types.py

@@ -12,6 +12,7 @@
     Message,
     MessageMetadata,
     RawMessage,
+    ThinkingChunk,
 )
 
 
@@ -237,3 +238,21 @@ def test_creation(self):
         assert raw.id == "raw-001"
         assert raw.thread_id == "thread-001"
         assert raw.raw["platform"] == "test"
+
+
+class TestThinkingChunk:
+    """Tests for ThinkingChunk dataclass."""
+
+    def test_defaults(self):
+        chunk = ThinkingChunk()
+        assert chunk.type == "thinking"
+        assert chunk.content == ""
+
+    def test_with_content(self):
+        chunk = ThinkingChunk(content="Analyzing the user's request")
+        assert chunk.type == "thinking"
+        assert chunk.content == "Analyzing the user's request"
+
+    def test_type_is_literal(self):
+        chunk = ThinkingChunk(content="step 1")
+        assert chunk.type == "thinking"