`ChildProcess.kill()` does not indicate failure when process has already exited

[kevgeoleo]

Version: Deno 2.7.11

Hi,

I would like to report a behavior in Deno that can be reproduced using the below snippet

import { spawn } from 'node:child_process';

const proc = spawn('echo', ['hi'], {
  stdio: 'inherit'
});

// Wait for the process to exit so it is no longer running
await new Promise((resolve, reject) => {
  proc.on('error', reject);
  proc.on('close', (code, signal) => {
    resolve({ code, signal });
  });
});

// Now attempt to send a signal to the already-exited process
try {
  const killed = proc.kill('SIGQUIT');
  if (!killed) {
    throw new Error('Failed to send SIGQUIT: process may have already exited');
  }
} catch (err) {
  // Normal, catchable JavaScript error
  console.error('Caught error when killing process:', err);
}

Expected behavior

root@KContainer:~/7362# node simple.mjs
hi
Caught error when killing process: Error: Failed to send SIGQUIT: process may have already exited
    at file:///home/c01kele/git/run/cerebras/deno/OPENAI/gpt5.1/filter/batch_2/cross_runtime/temp_node/7362/simple.mjs:23:11
    at process.processTicksAndRejections (node:internal/process/task_queues:103:5)

Actual behavior

root@KContainer:~/7362# deno run -A simple.mjs
hi