Bug: agent-runner spawn() calls likely fail on Windows for npm-installed CLI tools (.cmd shim / CreateProcess limitation)

[priyamkarn]

Summary

libs/agent-runner/{codex,opencode,openhands}.ts all spawn their respective
agent CLIs (codex, opencode, presumably the openhands binary) using Node's
child_process.spawn() without shell: true, e.g.:

const child = spawn("opencode", args, {
  cwd: input.cwd,
  env: input.env,
  stdio: ["ignore", "pipe", "inherit"],
});

This likely fails on Windows whenever the target CLI is installed the standard
way -- via npm install -g, which creates a .cmd shim rather than a native
.exe.

Why

spawn() without shell: true calls Windows' CreateProcess directly.
CreateProcess cannot execute .cmd/.bat files -- they aren't in native
executable (PE) format and require cmd.exe /c <file> as an intermediary to
run at all. This is an OS-level restriction, not a Node bug or version quirk.

How I found this

While building a test for a separate opencode fix (argv secret exposure), I
tried spawning a fake opencode.cmd stand-in the exact same way the real
runner does. It failed immediately with:

Error: spawn EINVAL
    at ChildProcess.spawn (node:internal/child_process:441:11)

reproduced on a real Windows machine (Node v24.16.0), not a POSIX simulation.
Since the real production spawn call uses the identical pattern
(spawn("opencode", args, { ...no shell:true... })), this points to the same
failure happening for real if opencode is npm-installed on Windows.

Impact

If confirmed, the background auto-memory-update hook (libs/hooks/worker.ts)
would silently fail on Windows for any platform whose CLI is npm-installed --
likely all three (codex, opencode, openhands installers all follow the
same spawn pattern). This is a portability/functional bug, not a security
issue -- separate root cause from #, even though
found in the same file.

Suggested fix

The standard solution for "spawn needs to work with .cmd/.bat shims on
Windows, cross-platform, without shell-injection risk" is the cross-spawn
npm package. It detects .cmd/.bat targets and handles the
cmd.exe /c wrapping (with correct argument escaping) automatically,
avoiding the injection risk that comes with a blanket shell: true.

Would apply to all three agent runners identically, since they share the
same spawn pattern.

To verify before fixing

• Confirm on a real Windows machine that a real, npm-installed opencode
  (or codex) actually reproduces this when triggered via
  greplica install + a real coding session (not just my synthetic
  .cmd stand-in).
• Check whether any of the three CLIs happen to ship a native .exe
  instead of an npm .cmd shim (would make this moot for that specific
  tool).

[swayamg20]

Hi @kushalpatil07 and @priyamkarn — is #153 still something you would like addressed? Current main still uses Node’s native spawn across the three agent runners, and CI only exercises Ubuntu. I also saw that #154 was self-closed after the rebase introduced TypeScript failures. If a fresh PR is welcome, I can preserve the newer spawn-error cleanup, introduce a shared cross-platform spawn path, and add Windows-specific regression coverage. Would you prefer all three runners in one PR?