diff --git a/TODO.md b/TODO.md
index e1f93f9..e69de29 100644
--- a/TODO.md
+++ b/TODO.md
@@ -1,2 +0,0 @@
-- [ ] When the parent agent/orchestrator is killed, all child processes spawned by it should also be killed.
-  - [ ] This should apply to when we detect the process dies, like if the user Ctrl + C's out.
diff --git a/internal/app/session.go b/internal/app/session.go
index 31658ce..acb5e5c 100644
--- a/internal/app/session.go
+++ b/internal/app/session.go
@@ -323,6 +323,54 @@ func (s *Session) reapChild(c *Child) {
 	c.markExited(err)
 	logf("child %s exited (err=%v)", c.ID, err)
 	s.emitExit(c)
+	s.killDescendantsOf(c.ID)
+}
+
+// killDescendantsOf terminates every still-live direct child of
+// parentID. SPEC §2: closing the patterm process tears down every
+// child it spawned; the same rule applies in-session — when an
+// orchestrator dies (natural exit, user Ctrl-C, MCP close, anything
+// that makes its PTY EOF), the agents/commands/terminals it spawned
+// must die with it. We only signal direct children here: each
+// descendant's own reapChild will fire and recurse, so the cascade
+// flows through arbitrary depth without us walking the tree.
+func (s *Session) killDescendantsOf(parentID string) {
+	if parentID == "" {
+		return
+	}
+	s.mu.Lock()
+	var live []*Child
+	for _, c := range s.children {
+		if c.ParentID == parentID && c.IsLive() {
+			live = append(live, c)
+		}
+	}
+	s.mu.Unlock()
+	if len(live) == 0 {
+		return
+	}
+	for _, c := range live {
+		_ = c.signal(syscall.SIGTERM)
+	}
+	deadline := time.Now().Add(2 * time.Second)
+	for time.Now().Before(deadline) {
+		anyLive := false
+		for _, c := range live {
+			if c.IsLive() {
+				anyLive = true
+				break
+			}
+		}
+		if !anyLive {
+			return
+		}
+		time.Sleep(20 * time.Millisecond)
+	}
+	for _, c := range live {
+		if c.IsLive() {
+			_ = c.signal(syscall.SIGKILL)
+		}
+	}
 }
 
 // Children returns a snapshot of children in spawn order.
diff --git a/internal/app/session_test.go b/internal/app/session_test.go
new file mode 100644
index 0000000..020ac30
--- /dev/null
+++ b/internal/app/session_test.go
@@ -0,0 +1,82 @@
+package app
+
+import (
+	"syscall"
+	"testing"
+	"time"
+)
+
+// TestParentExitKillsDescendants verifies that when a parent process
+// exits, every still-live process that was spawned under it is signaled
+// and dies, recursively through the tree.
+func TestParentExitKillsDescendants(t *testing.T) {
+	sess := NewSession(t.TempDir(), "test")
+
+	// Use a tiny pause-then-trap shell so the children survive long
+	// enough for the parent to die first; SIGTERM should terminate them.
+	sleepArgv := []string{"sh", "-c", "trap 'exit 0' TERM; sleep 30"}
+
+	parent, err := sess.Spawn(SpawnSpec{
+		Kind: KindTerminal,
+		Argv: []string{"sh", "-c", "sleep 30"},
+	}, 80, 24)
+	if err != nil {
+		t.Fatalf("spawn parent: %v", err)
+	}
+
+	childA, err := sess.Spawn(SpawnSpec{
+		Kind:     KindCommand,
+		Argv:     sleepArgv,
+		ParentID: parent.ID,
+	}, 80, 24)
+	if err != nil {
+		t.Fatalf("spawn childA: %v", err)
+	}
+	grandchild, err := sess.Spawn(SpawnSpec{
+		Kind:     KindCommand,
+		Argv:     sleepArgv,
+		ParentID: childA.ID,
+	}, 80, 24)
+	if err != nil {
+		t.Fatalf("spawn grandchild: %v", err)
+	}
+
+	// Wait for everyone to be running.
+	waitUntilLive(t, parent)
+	waitUntilLive(t, childA)
+	waitUntilLive(t, grandchild)
+
+	// Kill the parent. Its reapChild should cascade to childA, whose
+	// reapChild should in turn cascade to grandchild.
+	if err := parent.signal(syscall.SIGTERM); err != nil {
+		t.Fatalf("signal parent: %v", err)
+	}
+
+	waitUntilNotLive(t, parent)
+	waitUntilNotLive(t, childA)
+	waitUntilNotLive(t, grandchild)
+}
+
+func waitUntilLive(t *testing.T, c *Child) {
+	t.Helper()
+	deadline := time.Now().Add(5 * time.Second)
+	for time.Now().Before(deadline) {
+		if c.IsLive() {
+			return
+		}
+		time.Sleep(20 * time.Millisecond)
+	}
+	t.Fatalf("child %s never went live", c.ID)
+}
+
+func waitUntilNotLive(t *testing.T, c *Child) {
+	t.Helper()
+	deadline := time.Now().Add(5 * time.Second)
+	for time.Now().Before(deadline) {
+		if !c.IsLive() {
+			return
+		}
+		time.Sleep(20 * time.Millisecond)
+	}
+	t.Fatalf("child %s still live after parent died (status=%s)", c.ID, c.Status())
+}