WSL: Invalid Windows `start` command to open browser when showing a servable from running `asyncio` coroutine.

[emcd]

ALL software version info

(this library, plus any other relevant software, e.g. bokeh, python, notebook, OS, browser, etc)

$ uname -r
5.15.133.1-microsoft-standard-WSL2

$ hatch run python -V
Python 3.10.14

$ hatch run pip freeze | grep -E '^(bokeh|panel|param|tornado)'
bokeh==3.4.3
panel==1.4.5
param==2.1.1
tornado==6.4.1

Description of expected behavior and the observed behavior

Expected behavior (which is seen from inside synchronous function but not coroutine):

$ hatch run python panel-asyncio-bug.py
Launching server at http://localhost:34375
405 HEAD / (127.0.0.1) 0.41ms

Observed behavior (which is seen from inside of coroutine):

$ hatch run python panel-asyncio-bug.py
Launching server at http://localhost:41805
Start : This command cannot be run due to the error: The system cannot find the file specified.
At line:1 char:125
+ ... [System.Text.Encoding]::GetEncoding(); Start "http\localhost41805\"
+                                            ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (:) [Start-Process], InvalidOperationException
    + FullyQualifiedErrorId : InvalidOperationException,Microsoft.PowerShell.Commands.StartProcessCommand

Complete, minimal, self-contained example code that reproduces the issue

from asyncio import run
from panel.widgets import Button

async def setup( ): pass

def main( ):
    run( setup( ) )
    Button( name = 'foo' ).show( )

async def main_async( ):
    await setup( )
    Button( name = 'foo' ).show( )

#main( )                # Works.
run( main_async( ) )    # Broken.

• [x] I may be interested in making a pull request to address this (but don't count on it)

[emcd]

Maybe the server is dying for another reason and the invalid command is a red herring. However, my understanding is that Tornado 6 is asyncio-based and that Panel/Bokeh use the current event loop. I forced the logging configuration to level logging.DEBUG but do not see anything that indicates a failure of the server. On the surface, it would seem to be playing nicely with the existing event loop.

[emcd]

Tried the reproducer in a native Linux environment and it seems that the server is dying silently. The browser tab will actually open without problem but it points to empty content.