Pin a chart to the last few runs of a flow

backend/fluksio/flow/dashboards.py

@@ -33,6 +33,10 @@ DASHBOARD_DIR = "_dashboards"
 #: A chart cannot ask for an unbounded series; this is the ceiling.
 HISTORY_CAP = 5000
 
+#: How many runs one pinned chart puts side by side. The client's own
+#: ``MAX_SERIES``: the palette is five steps, and a sixth line repeats one.
+RUN_LINES = 5
+
 #: How many readings one bar draws. Mirrored in the client
 #: (``ui/core/config.ts``, ``MAX_ROWS``).
 #:
@@ -207,6 +211,17 @@ class WidgetDef(BaseModel):
         """A chart that asks a flow for its series instead of reading the ring."""
         return self.type == "chart" and self.config.get("source") == "query"
 
+    @property
+    def _runs_chart(self) -> bool:
+        """A chart pinned to runs: it reads the run tables, not the engine.
+
+        The other way round from opening a dashboard against a run — that is a
+        way of looking at a page, this is a tile that always shows the last
+        few runs of something, which is what a wall panel over a lab bench
+        wants.
+        """
+        return self.type == "chart" and self.config.get("source") == "runs"
+
     @property
     def inner_bindings(self) -> Bindings:
         """A bar's nested readings, as documents written before rows carry them.
@@ -245,6 +260,10 @@ class WidgetDef(BaseModel):
     @property
     def messages(self) -> list[str]:
         """Every message name this widget reads."""
+        if self._runs_chart:
+            # Its metric is a run's recorded series, which no live message
+            # carries — nothing for the engine to route or to keep.
+            return []
         if self._query_chart:
             name = self.config.get("message")
             return [str(name)] if name else []
@@ -280,7 +299,7 @@ class WidgetDef(BaseModel):
         Nothing, for a chart that queries: the answer carries its own past, so
         asking the engine to keep a ring as well would store it twice.
         """
-        if self.type != "chart" or self._query_chart:
+        if self.type != "chart" or self._query_chart or self._runs_chart:
             return 0
         points = int((self.config.get("history") or {}).get("points") or 0)
         return min(points, HISTORY_CAP)
@@ -304,6 +323,21 @@ class WidgetDef(BaseModel):
     @model_validator(mode="after")
     def _check_binding(self) -> WidgetDef:
         """Refuse a widget wired to a message it cannot carry."""
+        if self._runs_chart:
+            runs = self.config.get("runs") or {}
+            if not runs.get("metric"):
+                raise ValueError("a chart of runs must name the metric it draws")
+            if not (runs.get("ids") or runs.get("group") or runs.get("flow")):
+                raise ValueError(
+                    "a chart of runs must say which: a flow, a sweep, or run ids"
+                )
+            latest = int(runs.get("latest") or 1)
+            if not 1 <= latest <= RUN_LINES:
+                raise ValueError(f"a chart draws between 1 and {RUN_LINES} runs")
+            if len(runs.get("ids") or []) > RUN_LINES:
+                raise ValueError(f"a chart draws at most {RUN_LINES} runs")
+            return self
+
         if self._query_chart:
             for key, want in (("dtype", "series"), ("request_dtype", "record")):
                 bound = str(self.config.get(key) or "")
@@ -818,6 +852,7 @@ def results_dashboard(flow: FlowDef) -> DashboardDef:
 
 __all__ = [
     "BAR_ROWS",
+    "RUN_LINES",
     "COLOR_DTYPES",
     "DASHBOARD_DIR",
     "HISTORY_CAP",