Document the runs screen, the run context and the generated dashboard

docs/concepts/runs.md

@@ -286,6 +286,56 @@ acknowledgement was late is not recovery; instead a running run refreshes a
 lease, and one whose lease goes stale is marked `abandoned` — which is what a
 run whose engine was killed mid-training becomes.
 
+## Looking at what ran
+
+The **Runs** screen is the experiment log: every run newest-first, filtered by
+flow, by status, or down to one sweep. A sweep is worth filtering to — the
+table then draws a column per parameter that actually varied, which is what
+makes fifty runs of one flow readable.
+
+Tick two or more and their curves go side by side. That comparison is the
+address, so a link to it is a link someone else can open.
+
+One run in full is params, the per-node record with its logs and traceback,
+the artifacts it made, its metrics and its result.
+
+### A dashboard, read against runs
+
+A run records values under the same names a dashboard binds to — a run of
+`study` writes `study.loss` — so a dashboard is already a way of looking at
+one. **Open in dashboard** from a run or a comparison opens any dashboard with
+`?runs=a,b,c` on it, and the widgets resolve from those runs instead of from
+the live engine: each chart draws a line per run, the tiles that show one
+number show the first, and the controls go quiet because there is nothing left
+to publish to.
+
+Nothing about the dashboard is specific to runs. The page built to watch a
+training run happen is the page that shows the finished ones.
+
+If a flow has no dashboard yet, the same menu offers to build one from what
+the flow declares — a chart per streaming port, a tile per output:
+
+```
+POST /api/v1/dashboards/from-flow/study
+```
+
+It publishes `study_results` and is an ordinary dashboard afterwards; editing
+it is how it stops being generic.
+
+### A tile that always shows the last few
+
+The other direction is a chart pinned to runs rather than a page opened
+against them, which is what a panel over a bench wants. Set a chart's source
+to **Runs**, name the metric, and pick either the latest N of a flow, one
+sweep, or specific runs. It re-reads on its own and whenever a run finishes.
+
+### When a run draws nothing
+
+A node restored from the [stage cache](#stage-caching) replays no emissions —
+a cache hit returns what the node returned, not what it emitted on the way. So
+a run that reused an earlier one has a result and an empty curve, and the
+chart says so rather than looking broken.
+
 ## What this costs, compared
 
 The repository ships a benchmark that measures submitting a run against a