refactor(extensions): extract feishu dedup and mattermost onchar helpers

extensions/feishu/src/dedup.ts

@@ -0,0 +1,33 @@
+// Prevent duplicate processing when WebSocket reconnects or Feishu redelivers messages.
+const DEDUP_TTL_MS = 30 * 60 * 1000; // 30 minutes
+const DEDUP_MAX_SIZE = 1_000;
+const DEDUP_CLEANUP_INTERVAL_MS = 5 * 60 * 1000; // cleanup every 5 minutes
+const processedMessageIds = new Map<string, number>(); // messageId -> timestamp
+let lastCleanupTime = Date.now();
+
+export function tryRecordMessage(messageId: string): boolean {
+  const now = Date.now();
+
+  // Throttled cleanup: evict expired entries at most once per interval.
+  if (now - lastCleanupTime > DEDUP_CLEANUP_INTERVAL_MS) {
+    for (const [id, ts] of processedMessageIds) {
+      if (now - ts > DEDUP_TTL_MS) {
+        processedMessageIds.delete(id);
+      }
+    }
+    lastCleanupTime = now;
+  }
+
+  if (processedMessageIds.has(messageId)) {
+    return false;
+  }
+
+  // Evict oldest entries if cache is full.
+  if (processedMessageIds.size >= DEDUP_MAX_SIZE) {
+    const first = processedMessageIds.keys().next().value!;
+    processedMessageIds.delete(first);
+  }
+
+  processedMessageIds.set(messageId, now);
+  return true;
+}