Portable process spawning across macOS and Windows #28

Summary

The companion currently spawns opencode, node, and which directly. On Windows, npm-global binaries are usually .cmd shims (opencode.cmd, node may be outside the minimal PATH, etc.), and Node's spawn() with shell: false does not resolve .cmd wrappers.

This is the OpenCode equivalent of several upstream Codex plugin Windows issues.

Local evidence

Affected paths include:

• plugins/opencode/scripts/lib/process.mjs
  • resolveOpencodeBinary() uses spawn("which", ["opencode"])
  • getOpencodeVersion() uses spawn("opencode", ["--version"])
  • runCommand() uses spawn(cmd, args, ...) without Windows shim handling
  • spawnDetached() uses spawn(cmd, args, ...) for background node
• plugins/opencode/scripts/lib/opencode-server.mjs
  • ensureServer() uses spawn("opencode", ["serve", ...])

Expected behavior

Setup and runtime commands should work on Windows when OpenCode was installed through npm or another shim-based installer.

Suggested fix

Add a shared spawn helper that handles Windows command resolution deliberately:

1. Prefer direct executable resolution where possible (where opencode on Windows, command -v/which elsewhere).
2. For npm .cmd shims, use shell: true or resolve the concrete .cmd path only where needed.
3. Preserve UNC/network-drive behavior by avoiding blanket shell: true for all git subprocesses.
4. Add regression coverage around the command-building behavior.

Upstream references

Derived from these applicable upstream issues:

• Windows: spawnSync ENOENT — codex/npm not detected without shell:true openai/codex-plugin-cc#16
• /codex:setup reports npm and codex as "Missing" / "Not installed" on Windows (Claude Code + Git Bash) openai/codex-plugin-cc#17
• spawn codex ENOENT on Windows — app-server.mjs missing shell: true for .cmd wrapper resolution openai/codex-plugin-cc#32
• Windows: spawn codex ENOENT — missing shell: true in app-server.mjs openai/codex-plugin-cc#46
• spawn codex ENOENT on Windows: companion script fails to find codex CLI openai/codex-plugin-cc#50
• spawn() in app-server.mjs fails with ENOENT on Windows openai/codex-plugin-cc#53