feat(flows): improve workflow builder UX and diagnostics (#4574)

app/src/components/flows/workflowCopilotThreads.ts

@@ -0,0 +1,29 @@
+/**
+ * Session-lived cache of each workflow's copilot chat thread id, keyed by flow
+ * (a persisted flow id, or `'draft'` for an unsaved draft). The copilot panel
+ * unmounts when closed and `FlowEditor` remounts when switching flows, so
+ * without this the `workflow_builder` thread — and its transcript — would be
+ * lost on every open/close. Persisting the thread id lets the panel reseed the
+ * same thread (its messages live in the Redux `messagesByThreadId` store), so
+ * reopening the copilot restores the conversation for that workflow.
+ *
+ * Module-level (session) scope is deliberate: it survives component remounts
+ * without coupling to Redux, and a fresh session legitimately starts a new
+ * authoring conversation.
+ */
+const copilotThreadByFlow = new Map<string, string>();
+
+/** Cache key for a flow: its persisted id, or `'draft'` for an unsaved draft. */
+export function copilotThreadKey(flowId: string | null): string {
+  return flowId ?? 'draft';
+}
+
+export function getCopilotThreadId(flowId: string | null): string | null {
+  return copilotThreadByFlow.get(copilotThreadKey(flowId)) ?? null;
+}
+
+export function setCopilotThreadId(flowId: string | null, threadId: string | null): void {
+  const key = copilotThreadKey(flowId);
+  if (threadId) copilotThreadByFlow.set(key, threadId);
+  else copilotThreadByFlow.delete(key);
+}