VSC Notebooks vs. Positron Notebooks

System details:

Positron and OS details:

Positron Version: 2025.12.0 build 72
Code - OSS Version: 1.105.0
Commit: 3af147dca07686d2cfa80faf0796c04661c56616
Date: 2025-11-14T07:19:22.022Z
Electron: 37.6.0
Chromium: 138.0.7204.251
Node.js: 22.19.0
V8: 13.8.258.32-electron.0
OS: Darwin arm64 25.0.0

Describe the issue:

• Positron notebooks currently cannot render outputs that include the application/json mime type.
• Instead of displaying the JSON content, Positron shows an inline error:
  Can't handle mime type "application/json" yet
  This occurs both for:
• Custom display objects implementing _repr_mimebundle_ and IPython.display.JSON

Steps to reproduce the issue:

Case 1: Custom _repr_mimebundle_

from IPython.display import DisplayObject

class Weird(DisplayObject):
    def _repr_mimebundle_(self, include=None, exclude=None):
        return {
            "text/plain": "plain text repr",
            "application/json": {"x": 1, "y": 2},
            "text/html": "<b>HTML repr</b>"
        }

Weird()

Case 2: Using IPython.display.JSON

from IPython.display import JSON
JSON({"valid": 1, "bad": float("nan")}) # Even with valid JSON the error appears

Expected Behavior

• Positron should display the JSON object using the same viewer used in JupyterLab/Classic/VSC (a collapsible JSON tree).
• For invalid JSON (e.g., NaN), behavior should match Jupyter/VSC