Fix Windows path quoting for usernames with special characters

[Copilot]

The Jupyter extension was failing on Windows when usernames contained special characters like parentheses, ampersands, or other shell metacharacters. This occurred because executable paths weren't being properly quoted during process execution.

Problem

When Windows usernames contain special characters (e.g., John(Contractor)), the extension would fail with errors like:

'c:\Users\John' is not recognized as an internal or external command,
operable program or batch file.

This happened because the toCommandArgument() function only checked for spaces but ignored other shell metacharacters like parentheses (), ampersands &, pipes |, etc.

Root Cause

The issue was in src/platform/common/helpers.ts where toCommandArgument() used:

return value.indexOf(' ') >= 0 && !value.startsWith('"') && !value.endsWith('"') ? `"${value}"` : value.toString();

This meant paths like C:\Users\John(Contractor)\AppData\Local\env\python.exe were not being quoted, causing Windows command shell to split the path at the first space or special character.

Solution

Updated toCommandArgument() to check for all shell metacharacters that require quoting:

const needsQuoting = /[\s()&|<>^]/.test(value);
return needsQuoting && !value.startsWith('"') && !value.endsWith('"') ? `"${value}"` : value.toString();

Now paths with any special characters are properly quoted as "C:\Users\John(Contractor)\AppData\Local\env\python.exe".

Testing

Added comprehensive test coverage for:

• Windows paths with spaces in usernames
• Windows paths with parentheses (the specific issue case)
• Paths with other shell metacharacters (&, |, <, >, ^)
• Already quoted paths (prevents double-quoting)
• Normal paths without special characters

All existing tests continue to pass, ensuring no regressions.

Fixes #16932.

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