Record flags in history and draw them as steps

A bool was excluded from the history as "not a measurement", so a true/false
port had no curve in the node panel and none on an edge — only the word. It is
recorded as 0/1 now and drawn as steps, since a bezier through two states
slopes through readings that never happened. The axis is pinned to 0..1, so a
flag that was never on sits at the floor rather than mid-box.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

frontend/src/components/Common/Sparkline.tsx

@@ -28,15 +28,17 @@ const READOUT_DIGITS = 4
  * that never moved has no span to divide by, and one spanning decades is only
  * legible once the exponent is what varies.
  */
-function shape(points: HistoryPoint[]) {
+function shape(points: HistoryPoint[], step = false) {
   const values = points.map((point) => point.value)
   const low = Math.min(...values)
   const high = Math.max(...values)
   // Logs need every reading on the same side of zero.
-  const logged = low > 0 && high / low >= LOG_RATIO
+  const logged = !step && low > 0 && high / low >= LOG_RATIO
   const project = (value: number) => (logged ? Math.log10(value) : value)
-  const floor = project(low)
-  const span = project(high) - floor
+  // A flag's axis is the two values it has, so one that was never on sits at
+  // the floor rather than in the middle of the box the way a flat curve does.
+  const floor = step ? 0 : project(low)
+  const span = step ? 1 : project(high) - floor
 
   const y = (value: number) =>
     span === 0
@@ -46,10 +48,15 @@ function shape(points: HistoryPoint[]) {
     points.length === 1 ? 100 : (index / (points.length - 1)) * 100
 
   const line = points
-    .map(
-      (point, index) =>
-        `${index ? "L" : "M"}${x(index).toFixed(2)},${y(point.value).toFixed(2)}`,
-    )
+    .map((point, index) => {
+      const at = `${x(index).toFixed(2)},${y(point.value).toFixed(2)}`
+      if (!index) return `M${at}`
+      // A flag holds its last value until it changes, so it turns a corner
+      // rather than sloping through readings it never took.
+      return step
+        ? `L${x(index).toFixed(2)},${y(points[index - 1].value).toFixed(2)} L${at}`
+        : `L${at}`
+    })
     .join(" ")
 
   return {
@@ -79,6 +86,7 @@ export function Sparkline({
   height = "h-8",
   dot = true,
   readout = true,
+  bool = false,
 }: {
   points: HistoryPoint[]
   /** The token the curve, its area and the dot are drawn in. */
@@ -89,9 +97,11 @@ export function Sparkline({
   dot?: boolean
   /** The current value and the range, beside the curve. */
   readout?: boolean
+  /** A flag: drawn as steps between 0 and 1, and read as true/false. */
+  bool?: boolean
 }) {
   const id = useId()
-  const { low, high, line, area, end } = shape(points)
+  const { low, high, line, area, end } = shape(points, bool)
 
   return (
     // The gap leaves the live dot room to sit on the last reading without
@@ -181,10 +191,15 @@ export function Sparkline({
       {readout ? (
         <div className="min-w-24 shrink-0 whitespace-nowrap text-right font-mono text-xs leading-tight">
           <div className="font-medium">
-            {si(points[points.length - 1].value, READOUT_DIGITS)}
+            {bool
+              ? points[points.length - 1].value
+                ? "true"
+                : "false"
+              : si(points[points.length - 1].value, READOUT_DIGITS)}
           </div>
-          {/* A series that never moved has no range worth repeating. */}
-          {low === high ? null : (
+          {/* A series that never moved has no range worth repeating, and
+              "false–true" is not a range anyone reads. */}
+          {low === high || bool ? null : (
             <div className="text-muted-foreground">
               {si(low, READOUT_DIGITS)}–{si(high, READOUT_DIGITS)}
             </div>

frontend/src/components/Flow/EdgeInspector.tsx

@@ -132,11 +132,11 @@ export function EdgeInspector({
         </div>
 
         {/* The same curve the node panel draws for this message: one value
-            says little, how it has been moving says the rest. Only for a
-            number, because only numbers are recorded — for anything else the
-            sparkline falls through to its own copy of the value, which the
-            popover already shows below. */}
-        {typeof live?.value === "number" ? (
+            says little, how it has been moving says the rest. Only for what is
+            recorded — a number, or a flag as the steps between 0 and 1. For
+            anything else the sparkline falls through to its own copy of the
+            value, which the popover already shows below. */}
+        {typeof live?.value === "number" || typeof live?.value === "boolean" ? (
           <div className="mt-2">
             <MessageSparkline
               flow={flow}

frontend/src/components/Flow/MessageSparkline.tsx

@@ -83,11 +83,13 @@ export function MessageSparkline({
   const ts = live?.ts
   const value = live?.value
   useEffect(() => {
-    if (typeof value !== "number" || !ts) return
+    // A flag is recorded as 0/1, the way the server keeps it.
+    if ((typeof value !== "number" && typeof value !== "boolean") || !ts) return
+    const reading = Number(value)
     setTail((previous) =>
       previous[previous.length - 1]?.ts === ts
         ? previous
-        : [...previous, { ts, value }].slice(-WINDOW),
+        : [...previous, { ts, value: reading }].slice(-WINDOW),
     )
   }, [ts, value])
 
@@ -127,7 +129,10 @@ export function MessageSparkline({
     <Tooltip>
       <TooltipTrigger asChild>
         <div>
-          <Sparkline points={points} />
+          <Sparkline
+            points={points}
+            bool={dtype === "bool" || typeof live?.value === "boolean"}
+          />
         </div>
       </TooltipTrigger>
       <TooltipContent>{caption(points)}</TooltipContent>