Description

This fixes the double-escaping of backslashes in pixi run command arguments.

The issue was a mismatch between shlex::try_join's POSIX double-quote escaping and deno_task_shell's parsing. deno_task_shell doesn't unescape \\ to \ inside double quotes the way POSIX shells do.

The fix uses single quotes where possible (which preserve backslashes literally), and falls back to double quotes for strings containing single quotes.

Before: pixi run echo 'test\ntest' → test\\ntest (doubled backslash)
After: pixi run echo 'test\ntest' → test\ntest (correct)

Fixes #5054
Fixes #4579

How Has This Been Tested?

In CI and manually:

Old:

> pixi --version
pixi 0.59.0
> pixi run echo 'bar\qux\'
Error:   × failed to parse shell script. Task: 'echo "bar\\qux\\" '
  ╰─▶ Expected closing double quote.
        "bar\\qux\\"
        ~
> pixi run echo 'test\ntest'
test\\ntest

New:

> pixi run echo 'bar\qux\'
bar\qux\
> pixi run echo 'test\ntest'
test\ntest

AI Disclosure

• This PR contains AI-generated content.
  • I have tested any AI-generated content in my PR.
  • I take responsibility for any AI-generated content in my PR.

Tools: Claude Code Opus 4.5

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added sufficient tests to cover my changes.
• I have verified that changes that would impact the JSON schema have been made in schema/model.py.