chore: import upstream snapshot with attribution

examples/agent-durable/main_test.go

@@ -0,0 +1,48 @@
+package main
+
+import (
+	"bytes"
+	"io"
+	"os"
+	"strings"
+	"testing"
+)
+
+func TestDurableAgentExampleResumesWithoutReplayingTool(t *testing.T) {
+	out := captureStdout(t, main)
+	if !strings.Contains(out, "simulated process interruption after checkpointed tool call") {
+		t.Fatalf("example output %q did not show the initial interrupted run", out)
+	}
+	if !strings.Contains(out, "resumed reply: sku-123 is reserved; no duplicate reservation was made") {
+		t.Fatalf("example output %q did not show the resumed response", out)
+	}
+	if !strings.Contains(out, "tool executions: 1") {
+		t.Fatalf("example output %q did not prove the tool was not replayed", out)
+	}
+}
+
+func captureStdout(t *testing.T, fn func()) string {
+	t.Helper()
+
+	old := os.Stdout
+	r, w, err := os.Pipe()
+	if err != nil {
+		t.Fatalf("pipe stdout: %v", err)
+	}
+	os.Stdout = w
+
+	var buf bytes.Buffer
+	done := make(chan struct{})
+	go func() {
+		_, _ = io.Copy(&buf, r)
+		close(done)
+	}()
+
+	fn()
+
+	_ = w.Close()
+	os.Stdout = old
+	<-done
+	_ = r.Close()
+	return buf.String()
+}