Switching from columns view to another view loses column metadata

[akshayka]

Describe the bug

• Create a notebook with a two columns, and arrange cells across the columns
• Switch to a compact view and save.

Expected behavior:

• Column metadata is still persisted in the notebook file.

Actual behavior:

• Column metadata is erased from the file.

Environment

{
  "marimo": "0.10.16",
  "OS": "Darwin",
  "OS Version": "22.5.0",
  "Processor": "arm",
  "Python Version": "3.12.4",
  "Binaries": {
    "Browser": "131.0.6778.265",
    "Node": "v21.5.0"
  },
  "Dependencies": {
    "click": "8.1.8",
    "docutils": "0.21.2",
    "itsdangerous": "2.2.0",
    "jedi": "0.19.2",
    "markdown": "3.7",
    "narwhals": "1.23.0",
    "packaging": "24.2",
    "psutil": "6.1.1",
    "pygments": "2.19.1",
    "pymdown-extensions": "10.14.1",
    "pyyaml": "6.0.2",
    "ruff": "0.9.2",
    "starlette": "0.45.2",
    "tomlkit": "0.13.2",
    "typing-extensions": "4.12.2",
    "uvicorn": "0.34.0",
    "websockets": "14.2"
  },
  "Optional Dependencies": {}
}

Code to reproduce

import marimo

__generated_with = "0.10.16"
app = marimo.App(width="columns")


@app.cell(column=0)
def _():
    "1"
    return


@app.cell(column=1)
def _():
    "2"
    return


if __name__ == "__main__":
    app.run()