Don't steal focus when an agent spawns a child via MCP

internal/app/spawn_focus_test.go

@@ -0,0 +1,46 @@
+package app
+
+import (
+	"testing"
+)
+
+// TestOnChildSpawnedAgentChildKeepsFocus verifies that when a child is
+// spawned with a ParentID set (i.e. a patterm-managed agent caused the
+// spawn over MCP), OnChildSpawned does NOT steal viewport focus from
+// the currently focused child.
+func TestOnChildSpawnedAgentChildKeepsFocus(t *testing.T) {
+	sess := NewSession(t.TempDir(), "test")
+	st := &uiState{sess: sess}
+
+	parent := newChildEntry("p_parent", "parent", KindAgent, nil, nil, "", "", "")
+	st.focusedID = parent.ID
+	st.focusedName = parent.Name
+
+	subAgent := newChildEntry("p_sub", "sub", KindAgent, nil, nil, parent.ID, "", "")
+
+	st.OnChildSpawned(subAgent)
+
+	if got := st.focusedID; got != parent.ID {
+		t.Fatalf("agent-initiated spawn should not change focusedID: want %q, got %q", parent.ID, got)
+	}
+	if got := st.focusedName; got != parent.Name {
+		t.Fatalf("focusedName changed: want %q, got %q", parent.Name, got)
+	}
+}
+
+// TestOnChildSpawnedPaletteChildTakesFocus verifies the legacy path is
+// preserved: spawns with an empty ParentID (palette, restore, external
+// MCP caller) still auto-focus the new child.
+func TestOnChildSpawnedPaletteChildTakesFocus(t *testing.T) {
+	sess := NewSession(t.TempDir(), "test")
+	st := &uiState{sess: sess}
+	st.lastExit.Store(-1)
+
+	c := newChildEntry("p_new", "newchild", KindAgent, nil, nil, "", "", "")
+
+	st.OnChildSpawned(c)
+
+	if got := st.focusedID; got != c.ID {
+		t.Fatalf("palette-initiated spawn should auto-focus: want %q, got %q", c.ID, got)
+	}
+}