feat: distinguish system events from user messages

System events (heartbeats, cron triggers, webhooks, channel events)
now render as subtle inline notifications instead of full user bubbles.
Detection based on content patterns ([EVENT], [cron:], [HEARTBEAT], etc.).

src/lib/systemEvent.ts

@@ -0,0 +1,29 @@
+/**
+ * Detect whether a user-role message is actually a system event
+ * (heartbeat, webhook, cron, channel event, etc.) rather than
+ * a real human message.
+ */
+
+const SYSTEM_PATTERNS: RegExp[] = [
+  // Explicit markers
+  /^\[EVENT\b/i,
+  /\[from:\s*[^\]]*\(system\)\]/i,
+  /^\[HEARTBEAT\b/i,
+  /^\[cron:/i,
+  /^\[hook:/i,
+  /^\[webhook:/i,
+  /^\[sms-inbound\b/i,
+  /^\[teamspeak\b/i,
+
+  // Heartbeat prompt pattern (the standard OpenClaw heartbeat)
+  /^Read HEARTBEAT\.md if it exists/,
+
+  // System event envelope: [source:xxx]
+  /^\[source:\s*\w+\]/i,
+];
+
+export function isSystemEvent(text: string): boolean {
+  const trimmed = text.trim();
+  if (!trimmed) return false;
+  return SYSTEM_PATTERNS.some(pat => pat.test(trimmed));
+}