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/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(";")