2.6. Repeated spans become summary rows🔗

Individual events remain in the timeline. For comparison, repeated events are grouped by a stable structured key:

name, phase, activity, backend, dtype, device, module

Step numbers and shape arrays remain event metadata, so a thousand training steps do not turn into a thousand unrelated rows. Each group records call count, total inclusive and self time, minimum, mean, median, nearest-rank p95, maximum, heartbeat totals, and any memory counters supplied by an adapter.

This produces two complementary artifacts. The Trace Event file preserves temporal order and opens in Perfetto. The strict summary JSON preserves grouped measurements and validation state for scripts, CI, and baseline comparisons. The trace helps explain a run; the summary makes a repeated change measurable.