runPrettierStep breaks on shell-sensitive filenames

I ran across a potential issue in the wizard UI flow after the agent finishes making changes and the wizard tries to run the post-run formatting step.

From the user's perspective, this would show up near the end of a wizard run when the terminal says it is running Prettier on changed files. If one of the changed or untracked files has a name containing a space, quote, semicolon, or another shell-sensitive character, the formatting step may fail or format the wrong path.

I traced it in the repo to runPrettierStep: it gets changed/untracked files from git status --porcelain=v1, joins those filenames into one string, then interpolates that into a shell command:

childProcess.exec(
  `npx prettier --ignore-unknown --write ${changedOrUntrackedFiles}`,
  ...
)

Relevant code:

• src/utils/setup-utils.ts builds the changed-file list from Git status output.
• src/steps/run-prettier.ts joins that list and passes it to childProcess.exec.

This looks like it can break on ordinary filenames with spaces, quotes, or other shell-sensitive characters. It may also be worth checking whether a malicious filename could change what the shell executes, since the filenames are interpolated into the command string.

A simple reproduction should be something like:

1. In a test project, create or modify a file with a name containing a space, quote, semicolon, or other shell-sensitive character.
2. Ensure the project has Prettier declared in package.json.
3. Run a wizard flow that reaches the post-run Prettier step.
4. Observe whether Prettier formats the intended file, fails, or interprets the filename incorrectly.

I think the safer shape is probably to keep filenames as argv entries and use spawn/execFile instead of exec, but I have not fully tested the behavior yet.

Start by reading src/utils/setup-utils.ts to verify how git status output becomes the changed-file list, then inspect src/steps/run-prettier.ts and reproduce the wizard flow with a filename containing spaces or shell-sensitive characters. Confirm that the post-run step passes filenames safely as separate arguments, formats the intended files, and does not interpret filename contents as shell commands.