Python Environments causes invalid "Python 3.14.undefined" kernels and Jupyter hangs on "Connecting to kernel"

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## Description

After enabling the Python Environments extension, VS Code's Jupyter kernel picker detects kernels with names similar to:

> project-name (3.14.x) (Python 3.14.undefined)

When I select one of these kernels and run a notebook cell, the notebook remains stuck indefinitely at:

> Connecting to kernel...

Disabling the Python Environments extension and reloading VS Code resolves the issue. Jupyter notebooks then detect the expected kernels and run normally.

## Steps to reproduce

1. Install and enable the Python, Jupyter, and Python Environments extensions.
2. Open a `.ipynb` file in VS Code.
3. Open the kernel picker.
4. Observe a detected kernel named similar to `project-name (3.14.x) (Python 3.14.undefined)`.
5. Select that kernel.
6. Run any notebook cell.

## Actual behavior

- The detected kernel name contains `Python 3.14.undefined`.
- The notebook remains stuck at `Connecting to kernel...`.
- No cell is executed.

## Expected behavior

- Python environments should be detected with the correct Python version and kernel metadata.
- Selecting a valid environment should start the Jupyter kernel successfully.
- Invalid or incomplete kernel entries such as `Python 3.14.undefined` should not be shown.

## Workaround

Disable the Python Environments extension and reload VS Code. Kernel detection and notebook execution then work normally.

## Environment

- OS: Windows 11 25H2
- VS Code version: 1.138.0
- Python Environments extension version: 1.36.0
- Python extension version: 2026.4.0
- Jupyter extension version: 2025.9.1
- Python version: 3.14.7
- Environment type: uv
- Workspace type: local

## Additional information

The problem appears only while the Python Environments extension is enabled. Enabling or disabling that extension, without changing the notebook or Python environment, consistently reproduces or resolves the issue.

Inizia riproducendo il problema tramite il selettore dei kernel di VS Code, con le estensioni Python, Jupyter e Python Environments abilitate, utilizzando la configurazione dell’ambiente uv indicata. Traccia il modo in cui l’estensione Python Environments segnala i metadati del kernel e il modo in cui il selettore gestisce la voce `Python 3.14.undefined`. Il lavoro è completato quando gli ambienti validi mostrano la versione corretta e un kernel selezionato si connette ed esegue una cella del notebook.

Scritto dal modello di indicizzazione a partire dal testo della issue.