Flow canvas: mark streaming edges with a marching dash

A port with `stream` set publishes repeatedly during one execution, and
until now nothing on the canvas said so. `deriveEdges` carries the flag
from the producing `MessageSpec` onto the edge, `LiveEdge` turns it into
an `edge-stream` class, and the class draws a dashed stroke whose offset
marches toward the target. The pulse still lands on top: both animations
share one declaration when a value arrives on a streaming edge.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HTsT1isxUjw5gtkJk8WhuA

frontend/src/components/Flow/LiveEdge.tsx

@@ -34,7 +34,7 @@ function LiveEdgeComponent({
   data,
   selected,
 }: EdgeProps) {
-  const { message, producerId } = (data ?? {}) as FlowEdgeData
+  const { message, producerId, stream } = (data ?? {}) as FlowEdgeData
   const live = useLiveValue(message)
   const zoom = useStore((state) => state.transform[2])
   const [pulsing, setPulsing] = useState(false)
@@ -69,7 +69,7 @@ function LiveEdgeComponent({
       <BaseEdge
         id={id}
         path={path}
-        className={cn(pulsing && "edge-live")}
+        className={cn(pulsing && "edge-live", stream && "edge-stream")}
         style={selected ? { stroke: "var(--primary)" } : undefined}
       />
       {live !== undefined && zoom >= CHIP_MIN_ZOOM ? (

frontend/src/components/Flow/deriveEdges.ts

@@ -29,6 +29,8 @@ export type FlowEdgeData = {
   flow: string
   /** Whose publication this edge represents, so only it pulses. */
   producerId: string
+  /** The producing port publishes repeatedly during one run, not once at its end. */
+  stream?: boolean
   [key: string]: unknown
 }
 
@@ -40,14 +42,17 @@ export type FlowEdgeData = {
  * message therefore draw two edges converging on the same input.
  */
 export function deriveEdges(nodes: NodeDef_Input[], flow: string): Edge[] {
-  const producers = new Map<string, { node: string; port: string }[]>()
+  const producers = new Map<
+    string,
+    { node: string; port: string; stream?: boolean }[]
+  >()
 
   for (const node of nodes) {
     for (const spec of node.provides ?? []) {
       const message = qualify(flow, spec.name ?? "")
       if (!message) continue
       const list = producers.get(message) ?? []
-      list.push({ node: node.id, port: portOf(spec) })
+      list.push({ node: node.id, port: portOf(spec), stream: spec.stream })
       producers.set(message, list)
     }
   }
@@ -71,6 +76,7 @@ export function deriveEdges(nodes: NodeDef_Input[], flow: string): Edge[] {
             message,
             flow,
             producerId: `${flow}.${producer.node}`,
+            stream: producer.stream,
           } satisfies FlowEdgeData,
         })
       }
@@ -90,7 +96,7 @@ export function bindingsKey(nodes: NodeDef_Input[]): string {
         `${node.id}|${(node.requires ?? [])
           .map((s) => `${portOf(s)}=${s.name ?? ""}`)
           .join(",")}|${(node.provides ?? [])
-          .map((s) => `${portOf(s)}=${s.name ?? ""}`)
+          .map((s) => `${portOf(s)}=${s.name ?? ""}${s.stream ? "*" : ""}`)
           .join(",")}`,
     )
     .join(";")

frontend/src/components/Flow/flow.css

@@ -71,6 +71,32 @@
       stroke-width: var(--xy-edge-stroke-width);
     }
   }
+
+  /*
+   * An output that publishes repeatedly during one run reads as a march rather
+   * than a line. Only the dash offset moves, so the pulse above still shows
+   * through on the same path: it recolours and widens the dashes as they go.
+   * A loop rather than a one-shot, so none of the `--duration-*` tokens fit —
+   * the literal is one dash period per step, slow enough to read as direction.
+   */
+  .react-flow__edge-path.edge-stream {
+    stroke-dasharray: 6 4;
+    animation: edge-march 700ms linear infinite;
+  }
+
+  /* Both at once: one `animation` declaration has to carry both, or the
+     cascade keeps whichever rule came last and drops the other. */
+  .react-flow__edge-path.edge-stream.edge-live {
+    animation:
+      edge-pulse var(--duration-pulse) var(--ease-emphasized),
+      edge-march 700ms linear infinite;
+  }
+
+  @keyframes edge-march {
+    to {
+      stroke-dashoffset: -10;
+    }
+  }
 }
 
 /* A node that just published something says so, once, and settles. */