fix(cli): interrupt running commands cleanly on Ctrl+C

The launcher (bin/cli.js) spawns the real CLI as a child with inherited
stdio. Previously it was torn down by SIGINT before that child finished,
so the child's final status printed after the shell prompt had already
returned (and the child could be left running in the background).

Wait briefly for the child to handle the interrupt itself and mirror its
exit, so output stays ordered. The wait is bounded: if the child outlives
a short grace period, or on a second Ctrl+C, SIGKILL it and exit with the
conventional 128+signum code. The grace timer is unref'd, so a child that
exits on its own is mirrored with no added latency.

Author: jfblaa

bin/cli.js

@@ -38,9 +38,39 @@ void (async () => {
     },
   )
 
+  // The child shares our process group and handles the signal itself; wait briefly for it
+  // to exit (so its final output isn't printed after the prompt returns) and mirror its
+  // exit below. SIGKILL and leave if it outlasts the grace, or on a second signal.
+  const SHUTDOWN_GRACE_MS = 3_000
+  const hardAbort = signalName => {
+    const child = spawnPromise.process
+    if (child.exitCode === null && child.signalCode === null) {
+      child.kill('SIGKILL')
+    }
+    // eslint-disable-next-line n/no-process-exit
+    process.exit(signalName === 'SIGTERM' ? 143 : 130)
+  }
+  let sawSignal = false
+  const onSignal = signalName => {
+    if (sawSignal) {
+      hardAbort(signalName)
+      return
+    }
+    sawSignal = true
+    setTimeout(() => hardAbort(signalName), SHUTDOWN_GRACE_MS).unref?.()
+  }
+  const onSigint = () => onSignal('SIGINT')
+  const onSigterm = () => onSignal('SIGTERM')
+  process.on('SIGINT', onSigint)
+  process.on('SIGTERM', onSigterm)
+
   // See https://nodejs.org/api/child_process.html#event-exit.
   spawnPromise.process.on('exit', (code, signalName) => {
     if (signalName) {
+      // Mirror a signal death. Drop our own handlers first so the re-raise actually
+      // terminates us instead of being swallowed by onSigint/onSigterm above.
+      process.removeListener('SIGINT', onSigint)
+      process.removeListener('SIGTERM', onSigterm)
       process.kill(process.pid, signalName)
     } else if (typeof code === 'number') {
       // eslint-disable-next-line n/no-process-exit