Say what caused a value, and draw what is not a node

Moving a dashboard slider lit up an edge between two nodes that had done
nothing. The canvas pulsed on the message's timestamp alone, and a message
has no idea who published it — so it credited whichever node happened to
be drawn as a producer.

That was never only about dashboards. Two nodes producing one message
pulsed both their edges whichever fired, and a message produced in another
flow changed with nothing on screen to account for it at all.

Values now carry their cause: a node, a dashboard widget, another flow, an
agent or an API caller. An edge pulses only for the producer that actually
published, and the edge inspector says where a value came from when it did
not come from a node.

What is not a node in this flow is now drawn as one — a label rather than
a card, because a dashboard with twenty tiles would otherwise bury the
logic the canvas exists to show. That covers cross-flow wiring too, which
is the link in/out affordance that has been missing.

They are never part of the document. They join at render, after everything
that reads or writes the canvas nodes, so an autosave, an undo or a delete
cannot reach them — with a Playwright test that drags a node and asserts
the stored flow still holds exactly what it did.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011LF61rxW1FG5YCD2J9YqjY

frontend/src/components/Flow/liveStore.ts

@@ -8,7 +8,18 @@ import { useSyncExternalStore } from "react"
  * nothing else.
  */
 
-export type LiveValue = { value: unknown; ts: number | null }
+/** Who caused a value. The canvas needs it to pulse the right edge. */
+export type ValueSource = {
+  kind: "node" | "dashboard" | "flow" | "agent" | "api"
+  id: string
+  label: string
+  detail?: string
+}
+export type LiveValue = {
+  value: unknown
+  ts: number | null
+  source?: ValueSource
+}
 export type LiveStatus = {
   status: "active" | "error" | "running" | "success"
   error?: string | null