/observability/runs gains since/until, so the throughput chart's pin asks
the server for its minute instead of filtering a fixed recent list. This
engine writes ~60 runs a minute, so any minute but the newest read empty.
since is inclusive and until exclusive, matching the minute buckets the
charts are drawn from. Hover stays the client-side preview it was:
scrubbing a day would otherwise be a request per minute rested on.