fix: emit delta-only node system events

src/infra/system-events.ts

@@ -7,10 +7,30 @@ type SystemEvent = { text: string; ts: number };
 const MAX_EVENTS = 20;
 const queue: SystemEvent[] = [];
 let lastText: string | null = null;
+let lastContextKey: string | null = null;
 
-export function enqueueSystemEvent(text: string) {
+type SystemEventOptions = {
+  contextKey?: string | null;
+};
+
+function normalizeContextKey(key?: string | null): string | null {
+  if (!key) return null;
+  const trimmed = key.trim();
+  if (!trimmed) return null;
+  return trimmed.toLowerCase();
+}
+
+export function isSystemEventContextChanged(
+  contextKey?: string | null,
+): boolean {
+  const normalized = normalizeContextKey(contextKey);
+  return normalized !== lastContextKey;
+}
+
+export function enqueueSystemEvent(text: string, options?: SystemEventOptions) {
   const cleaned = text.trim();
   if (!cleaned) return;
+  lastContextKey = normalizeContextKey(options?.contextKey);
   if (lastText === cleaned) return; // skip consecutive duplicates
   lastText = cleaned;
   queue.push({ text: cleaned, ts: Date.now() });
@@ -21,6 +41,7 @@ export function drainSystemEvents(): string[] {
   const out = queue.map((e) => e.text);
   queue.length = 0;
   lastText = null;
+  lastContextKey = null;
   return out;
 }