fix: restore regressions from discord-only refactor

src/bot-message-filter.ts

@@ -0,0 +1,31 @@
+import { isSessionCommandControlMessage } from './session-commands.js';
+import { NewMessage } from './types.js';
+
+/**
+ * Filter messages before processing.
+ * - Normal rooms: drop all bot messages.
+ * - Paired rooms (allowBotMessages=true): keep other bot's messages,
+ *   but drop messages authored by this service's own bot (via isOwnMessage).
+ */
+export function filterProcessableMessages(
+  messages: NewMessage[],
+  allowBotMessages: boolean,
+  isOwnMessage?: (msg: NewMessage) => boolean,
+): NewMessage[] {
+  const withoutControlMessages = messages.filter(
+    (message) =>
+      !(
+        message.is_bot_message &&
+        isSessionCommandControlMessage(message.content)
+      ),
+  );
+
+  if (allowBotMessages) {
+    // In paired rooms, allow other bot messages but filter own bot's output
+    if (isOwnMessage) {
+      return withoutControlMessages.filter((m) => !isOwnMessage(m));
+    }
+    return withoutControlMessages;
+  }
+  return withoutControlMessages.filter((message) => !message.is_bot_message);
+}