diff --git a/nodejs/src/types.ts b/nodejs/src/types.ts
index 406fe8d5..413c1aaa 100644
--- a/nodejs/src/types.ts
+++ b/nodejs/src/types.ts
@@ -497,13 +497,30 @@ export interface MessageOptions {
     prompt: string;
 
     /**
-     * File or directory attachments
-     */
-    attachments?: Array<{
-        type: "file" | "directory";
-        path: string;
-        displayName?: string;
-    }>;
+     * File, directory, or selection attachments
+     */
+    attachments?: Array<
+        | {
+              type: "file";
+              path: string;
+              displayName?: string;
+          }
+        | {
+              type: "directory";
+              path: string;
+              displayName?: string;
+          }
+        | {
+              type: "selection";
+              filePath: string;
+              displayName: string;
+              selection?: {
+                  start: { line: number; character: number };
+                  end: { line: number; character: number };
+              };
+              text?: string;
+          }
+    >;
 
     /**
      * Message delivery mode
diff --git a/python/copilot/types.py b/python/copilot/types.py
index bb64dd98..668ffe43 100644
--- a/python/copilot/types.py
+++ b/python/copilot/types.py
@@ -24,13 +24,45 @@
 LogLevel = Literal["none", "error", "warning", "info", "debug", "all"]
 
 
-# Attachment type
-class Attachment(TypedDict):
-    type: Literal["file", "directory"]
+# Selection range for text attachments
+class SelectionRange(TypedDict):
+    line: int
+    character: int
+
+
+class Selection(TypedDict):
+    start: SelectionRange
+    end: SelectionRange
+
+
+# Attachment types - discriminated union based on 'type' field
+class FileAttachment(TypedDict):
+    """File attachment."""
+    type: Literal["file"]
+    path: str
+    displayName: NotRequired[str]
+
+
+class DirectoryAttachment(TypedDict):
+    """Directory attachment."""
+    type: Literal["directory"]
     path: str
     displayName: NotRequired[str]
 
 
+class SelectionAttachment(TypedDict):
+    """Selection attachment with text from a file."""
+    type: Literal["selection"]
+    filePath: str
+    displayName: str
+    selection: NotRequired[Selection]
+    text: NotRequired[str]
+
+
+# Attachment type - union of all attachment types
+Attachment = Union[FileAttachment, DirectoryAttachment, SelectionAttachment]
+
+
 # Options for creating a CopilotClient
 class CopilotClientOptions(TypedDict, total=False):
     """Options for creating a CopilotClient"""
diff --git a/python/test_session_events.py b/python/test_session_events.py
new file mode 100644
index 00000000..703beb9e
--- /dev/null
+++ b/python/test_session_events.py
@@ -0,0 +1,97 @@
+"""
+Unit tests for generated session event types.
+
+Tests for parsing session events and their data structures from the generated
+session_events.py module.
+"""
+
+
+from copilot.generated.session_events import (
+    Attachment,
+    AttachmentType,
+    SessionEventType,
+)
+
+
+class TestSessionEventTypes:
+    """Test session event type enum values."""
+
+    def test_session_start_event_type(self):
+        """The session.start event type should be recognized."""
+        assert SessionEventType.SESSION_START.value == "session.start"
+
+    def test_session_snapshot_rewind_event_type(self):
+        """The session.snapshot_rewind event type should be recognized."""
+        assert SessionEventType.SESSION_SNAPSHOT_REWIND.value == "session.snapshot_rewind"
+
+    def test_session_usage_info_event_type(self):
+        """The session.usage_info event type should be recognized."""
+        assert SessionEventType.SESSION_USAGE_INFO.value == "session.usage_info"
+
+
+class TestAttachmentTypes:
+    """Test attachment type parsing from generated session_events module."""
+
+    def test_file_attachment_parsing(self):
+        """Test parsing a file attachment."""
+        attachment_dict = {
+            "type": "file",
+            "path": "/path/to/file.py",
+            "displayName": "file.py",
+        }
+
+        attachment = Attachment.from_dict(attachment_dict)
+        assert attachment.type == AttachmentType.FILE
+        assert attachment.path == "/path/to/file.py"
+        assert attachment.display_name == "file.py"
+
+    def test_directory_attachment_parsing(self):
+        """Test parsing a directory attachment."""
+        attachment_dict = {
+            "type": "directory",
+            "path": "/path/to/dir",
+            "displayName": "dir",
+        }
+
+        attachment = Attachment.from_dict(attachment_dict)
+        assert attachment.type == AttachmentType.DIRECTORY
+        assert attachment.path == "/path/to/dir"
+        assert attachment.display_name == "dir"
+
+    def test_selection_attachment_parsing(self):
+        """Test parsing a selection attachment with all fields."""
+        attachment_dict = {
+            "type": "selection",
+            "filePath": "/path/to/file.py",
+            "displayName": "file.py:10-20",
+            "selection": {
+                "start": {"line": 10, "character": 0},
+                "end": {"line": 20, "character": 50},
+            },
+            "text": "selected text content",
+        }
+
+        attachment = Attachment.from_dict(attachment_dict)
+        assert attachment.type == AttachmentType.SELECTION
+        assert attachment.file_path == "/path/to/file.py"
+        assert attachment.display_name == "file.py:10-20"
+        assert attachment.selection is not None
+        assert attachment.selection.start.line == 10
+        assert attachment.selection.start.character == 0
+        assert attachment.selection.end.line == 20
+        assert attachment.selection.end.character == 50
+        assert attachment.text == "selected text content"
+
+    def test_selection_attachment_minimal(self):
+        """Test parsing a selection attachment with only required fields."""
+        attachment_dict = {
+            "type": "selection",
+            "filePath": "/path/to/file.py",
+            "displayName": "file.py",
+        }
+
+        attachment = Attachment.from_dict(attachment_dict)
+        assert attachment.type == AttachmentType.SELECTION
+        assert attachment.file_path == "/path/to/file.py"
+        assert attachment.selection is None
+        assert attachment.text is None