[cristianchiriac]

Fixes #973.

parseArgs stores a "Command line" in the SVG metadata. Its cliQuote() writes the layout's newlines as a literal \n, so the command fits on one line. TrayLayout.prepare() splits --layout only on real newlines, so running that command again reads the whole grid as one line and fails with ValueError: Need more than one wall in y direction.

prepare() now turns a literal \n back into a newline when the layout has no real newline, which is exactly the shape cliQuote() produces. A hand-written layout or a layout from the web form contains real newlines and is left untouched, and the layout characters never include a backslash. GridfinityTrayLayout inherits the fix. I left cliQuote() alone: it has no portable way to put a newline into a one-line shell command, since $'…' is bash-only and shlex can't parse it.

This is separate from #974, which changes the --layout default for #972. That PR also touches tests/test_traylayout.py, so whichever lands second may need a small merge.

Test: test_command_line_from_svg_can_be_run_again renders the layout and takes the stored metadata["cli"]. It asserts that the stored --layout argument contains a literal \n and no real newline, splits the command with shlex, and renders it again. The x, y, hwalls, vwalls and floors must match the original.

• before: ValueError: Need more than one wall in y direction, the error from the issue
• after: passes. The full suite has 205 passed and 9 skipped, and ruff check and mypy are clean on the changed files.

[florianfesti]

I am not quite sure what work flow you are using to need this. But it is the right thing to do - especially given that we do produce the CLI ourselves.