Reopening notebook thinks cells are redefined

### Describe the bug If I run a notebook in a tab, close and reopen the tab, then run a cell again, Marimo thinks the variables in the cell have already been defined and won't let the cell run. Restarting the kernel doesn't fix this. ### Environment <details> ``` marimo VS Code Extension Diagnostics ===================================== Language Server (LSP): UV Bin: Bundled (c:\Users\Andrew\.vscode\extensions\marimo-team.vscode-marimo-0.12.6-win32-x64\bundled\libs\bin\uv.exe) UV: 0.11.3 (45da18ac3 2026-04-01) ✓ Using bundled marimo-lsp via uvx Python Extension: Interpreter: c:\Users\Andrew\Code\biaxial-bioreactor\code\.venv\Scripts\python.exe Version: 3.13.9.final.0 Environment: VirtualEnvironment (biaxtic) Python Language Server (ty): Status: running ✓ Version: 0.0.26 (940305127 2026-03-26) Binary: UvInstalled (c:\Users\Andrew\AppData\Roaming\Code\User\globalStorage\marimo-team.vscode-marimo\libs\bin\ty.exe) Python: c:\Users\Andrew\Code\biaxial-bioreactor\code\.venv\Scripts\python.exe (3.13.9.final.0) Ruff Language Server: Status: running ✓ Version: 0.15.10 Binary: CompanionExtension/bundled (charliermarsh.ruff, c:\Users\Andrew\.vscode\extensions\charliermarsh.ruff-2026.40.0-win32-x64\bundled\libs\bin\ruff.exe) Extension Configuration: Version: 0.12.6 UV integration disabled: false System Information: Host: desktop IDE: Visual Studio Code IDE version: 1.116.0 Platform: win32 Architecture: x64 Node version: v22.22.1 Common Issues: 1. If notebooks won't open: - Check Python interpreter is selected - Ensure marimo is installed - Check 'marimo-lsp' output channel for errors 2. If features are missing: - Ensure marimo version is >= 0.23.2 - Try reloading the window ``` </details> ### Steps to reproduce _No response_