Add internal code mode module for programmatic notebook control

marimo/_code_mode/__init__.py

@@ -0,0 +1,45 @@
+# Copyright 2026 Marimo. All rights reserved.
+"""Code mode: programmatic notebook editing via async context manager.
+
+.. warning::
+
+    **Internal, agent-only API.** Not part of marimo's public API.
+    No versioning guarantees. May change or be removed without notice.
+
+Usage::
+
+    import marimo._code_mode as cm
+
+    async with cm.get_context() as ctx:
+        # Create cells (appends at end by default)
+        cid = ctx.create_cell("x = 1")
+        ctx.create_cell("y = x + 1", after=cid)
+
+        # Update cells by ID or name
+        ctx.edit_cell("my_cell", code="z = 42")
+
+        # Delete cells
+        ctx.delete_cell("old_cell")
+
+        # Move cells
+        ctx.move_cell("my_cell", after="other_cell")
+
+    # Read cells (works outside the context manager too)
+    ctx = cm.get_context()
+    ctx.cells[0]  # by index
+    ctx.cells["my_cell"]  # by name
+"""
+
+from __future__ import annotations
+
+from marimo._code_mode._context import (
+    AsyncCodeModeContext,
+    NotebookCellData,
+    get_context,
+)
+
+__all__ = [
+    "AsyncCodeModeContext",
+    "NotebookCellData",
+    "get_context",
+]