fix(hook): support OpenCode Desktop (Node.js) in plugin

[synnks]

Summary

• Fix OpenCode plugin failing silently in the Desktop app (Electron/Node.js)
• Add node:child_process fallback when Bun.$ is unavailable

Fixes #2039

Root Cause

OpenCode Desktop runs its server in an Electron utility process (Node.js), not Bun.
OpenCode passes $: undefined to plugins when typeof Bun === "undefined".
The plugin calls await $which rtk.quiet() — since $ is undefined, this throws a TypeError, caught by the catch block with the misleading message "rtk binary not found in PATH".

Test plan

• cargo fmt --all && cargo clippy --all-targets && cargo test
• node --experimental-strip-types --test hooks/opencode/tests/rtk.test.ts
• Manual testing: verified in OpenCode TUI (Bun path) and Desktop (child_process path)

[CLAassistant]

All committers have signed the CLA.

[alexandre-leites]

Any workaround while this is not merged?

[aurelienpolletadeo]

I am using this version of the rtk.ts for opencode desktop and it's working fine.
Waiting for merge.
Thanks for the PR!

[smzh369]

which may failed to get the path on Windows, better to make a platform judgement(line 29-33):

    const check = process.platform === "win32" ? "where" : "which"
    if ($) {
      await $`${check} rtk`.quiet()
    } else {
      execFileSync(check, ["rtk"], { encoding: "utf8", timeout: 5000 })
    }

[amnesiaof]

Same root causes reproduce on Windows CLI (not only Desktop Electron): no $ in plugin context + Unix-only which. Also note rtk rewrite exit-code-3 semantics — stdout must be captured from the exception. #3330's cross-platform process API fixes the CLI case too; verified with a working workaround.