fix(subprocess): clean managed processes on host exit

packages/subprocess/subprocess-local/tests/fixtures/managed-tree.ts

@@ -0,0 +1,16 @@
+import { spawn } from 'node:child_process'
+import { writeFile } from 'node:fs/promises'
+
+const [statePath] = process.argv.slice(2)
+if (statePath === undefined) throw new Error('usage: managed-tree.ts <state-path>')
+
+process.on('SIGTERM', () => {})
+process.on('SIGHUP', () => {})
+const descendant = spawn(process.execPath, [
+  '-e',
+  'process.on("SIGTERM",()=>{});process.on("SIGHUP",()=>{});setInterval(()=>{},60_000)',
+], { stdio: 'ignore' })
+if (descendant.pid === undefined) throw new Error('managed descendant did not publish a pid')
+
+await writeFile(statePath, JSON.stringify({ root: process.pid, descendant: descendant.pid }))
+setInterval(() => {}, 60_000)