diff --git a/src/main/windows/windows-pty-job.win32.test.ts b/src/main/windows/windows-pty-job.win32.test.ts
new file mode 100644
index 00000000000..a7514048cdb
--- /dev/null
+++ b/src/main/windows/windows-pty-job.win32.test.ts
@@ -0,0 +1,123 @@
+import { afterEach, describe, expect, it } from 'vitest'
+import type { IPty } from 'node-pty'
+import {
+  isPtyJobOwnershipAvailable,
+  listPtyJobProcessIds,
+  terminatePtyJob
+} from './windows-pty-job'
+
+/**
+ * The unit tests pin the contract; this pins the thing the contract is for.
+ *
+ * A grandchild spawned `detached` leaves the pane's console and reparents, so
+ * neither `GetConsoleProcessList` nor a parent-pid walk can see it. That is the
+ * process that outlived its pane and held the worktree directory open
+ * (#9045, #10475, #10897). Job membership is the only mechanism that finds it,
+ * so the assertion below is the whole justification for the node-pty patch.
+ *
+ * Runs only on win32; skipped elsewhere.
+ */
+const describeOnWindows = process.platform === 'win32' ? describe : describe.skip
+
+const sleep = (ms: number): Promise<void> => new Promise((resolve) => setTimeout(resolve, ms))
+
+function isAlive(pid: number): boolean {
+  try {
+    process.kill(pid, 0)
+    return true
+  } catch {
+    return false
+  }
+}
+
+describeOnWindows('ConPTY job ownership', () => {
+  const spawned: IPty[] = []
+
+  afterEach(() => {
+    for (const proc of spawned.splice(0)) {
+      try {
+        proc.kill()
+      } catch {
+        /* already gone */
+      }
+    }
+  })
+
+  async function spawnShellWithDetachedGrandchild(): Promise<{
+    proc: IPty
+    grandchildPid: number
+  }> {
+    const nodePty = await import('node-pty')
+    const proc = nodePty.spawn('cmd.exe', [], {
+      name: 'xterm-256color',
+      cols: 80,
+      rows: 30,
+      cwd: process.cwd(),
+      useConptyDll: true
+    })
+    spawned.push(proc)
+
+    let grandchildPid: number | null = null
+    proc.onData((chunk) => {
+      const match = /ORCA_GC=(\d+)/.exec(chunk)
+      if (match && grandchildPid === null) {
+        grandchildPid = Number(match[1])
+      }
+    })
+
+    const script = [
+      "const{spawn}=require('child_process');",
+      "const c=spawn(process.execPath,['-e','setInterval(()=>{},1000)'],",
+      "{detached:true,stdio:'ignore'});",
+      "c.unref();console.log('ORCA_GC='+c.pid);"
+    ].join('')
+    proc.write(`node -e "${script}"\r`)
+
+    for (let attempt = 0; attempt < 80 && grandchildPid === null; attempt += 1) {
+      await sleep(250)
+    }
+    if (grandchildPid === null) {
+      throw new Error('grandchild never reported its pid')
+    }
+    // Let the shell settle so the pid list is not read mid-spawn.
+    await sleep(1_000)
+    return { proc, grandchildPid }
+  }
+
+  it('reports this build as able to own pty trees', () => {
+    // A node-pty rebuilt from unpatched sources would silently fall back to the
+    // old probe, so every assertion below would pass vacuously.
+    expect(isPtyJobOwnershipAvailable()).toBe(true)
+  })
+
+  it('counts a detached grandchild as part of the pane tree', async () => {
+    const { proc, grandchildPid } = await spawnShellWithDetachedGrandchild()
+
+    const pids = listPtyJobProcessIds(proc)
+    expect(pids).not.toBeNull()
+    expect(pids).toContain(proc.pid)
+    expect(pids).toContain(grandchildPid)
+  }, 60_000)
+
+  it('kills the shell and the detached grandchild in one call', async () => {
+    const { proc, grandchildPid } = await spawnShellWithDetachedGrandchild()
+    expect(isAlive(grandchildPid)).toBe(true)
+
+    expect(terminatePtyJob(proc)).toBe('terminated')
+    await sleep(1_500)
+
+    expect(isAlive(proc.pid)).toBe(false)
+    expect(isAlive(grandchildPid)).toBe(false)
+  }, 60_000)
+
+  it('reports an emptied tree as empty, not as unavailable', async () => {
+    // Empty is evidence the pane is gone; null is the absence of evidence.
+    // A registry that cannot tell them apart keeps reporting dead terminals as
+    // connected (#15549).
+    const { proc } = await spawnShellWithDetachedGrandchild()
+    terminatePtyJob(proc)
+    await sleep(1_500)
+
+    expect(listPtyJobProcessIds(proc)).toEqual([])
+  }, 60_000)
+})