This was exactly the right shakeout before the Buenos Aires 21K: 5.5 km at a relaxed 7:01/km, with fresh legs, good sleep, low heart rate, and no unnecessary fatigue.
The GPS may have been noisy, but the lap pattern shows a calm and even effort. The run did its job: wake the legs up without spending the race.
The next session is the official half marathon. It replaces Garmin's long-run prescription completely; there is no need to add distance afterward.
Takeaway. Arrive calm and race progressively. The fitness is already there, so the key is not to burn the race in the first 5 km.
Next step. 21K Buenos Aires. Official half marathon race. Start controlled, build through the middle, and only race hard after 15-16 km if the body is responding well.