fix: run prettier without a shell so filenames can't be executed

[ryanwaits]

Fixes #800

Problem

Two bugs, and the one that isn't in the issue is the one that bites everyone.

The parser breaks before the shell sees a path. git C-quotes anything with a space or a non-ASCII byte, /^\S+\s+(\S+)/ only takes the first token, and renames yield the pre-rename path. So an ordinary rename plus a delete is enough: prettier gets keep.ts oldname.ts "to, the shell hits an unterminated quote, exit 2, nothing formatted.

Then the reported bug. Filenames are interpolated into exec. Spaces get quoted by git, but ;, >, | and $ don't, so a file named a.ts;>PWNED executes the redirect.

Fix

Read git status --porcelain=v1 -z and pass filenames as argv entries instead of interpolating them into a shell command.

-z is git's documented machine-parsing format: no quoting, reversed rename order, guaranteed stable across versions and user config. Keep the post-rename path, skip deletes. Run prettier's CLI under process.execPath via execFile with shell: false, plus -- so a leading-dash filename isn't read as a flag.

execFile('npx', ...) was the smaller diff, but it puts the shell back on Windows, where npx is npx.cmd. Resolving prettier from node_modules avoids that everywhere.

Testing

10 new tests in setup-utils.test.ts; 8 fail on main. End to end on a repo with a rename, a delete, with space.ts and a.ts;>PWNED: before, shell error, nothing formatted. After, exit 0, all formatted, no PWNED. Build, tests and lint are green.

Caveat

Prettier declared but not resolvable from node_modules now returns quietly instead of letting npx fetch it. That covers running before install, and Yarn PnP, which has no node_modules at all. Happy to add an npx fallback on non-Windows, where execFile can reach it without a shell.

[gewenyu99]

Yeah this is a weird one eh? Maybe it's time to hand this off to a subagent to come up with the environment specific linter calls... We've had quite a few issues with these tools

[ryanwaits]

yeah the step shells out and it assumes prettier, and this only fixes the shelling out.

the assumption is the bigger one imo. hasDeclaredDependency('prettier') means a project on biome, or dprint, or plain eslint --fix, silently gets nothing. biome is already in the agent's safe-tools allowlist, so the agent can run it but the format step can't.

detecting the project's own formatter and running its binary out of node_modules feels like the right shape. happy to pick that up as a follow-up, though it probably warrants its own issue rather than growing this one? just lmk!

[gewenyu99]

Yeah, I'm gonna review this one as is. That is a separate issue all together.