appendChatMessage: throw explicit error instead of getPadSafe (review)

Per review: replace the getPadSafe(padID, true) existence check with an
explicit `throw new CustomError('padID does not exist', 'apierror')` so chat
messages can't create pads, without fetching the pad.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: JohnMcLear

src/node/db/API.ts

@@ -414,11 +414,13 @@ exports.appendChatMessage = async (padID: string, text: string|object, authorID:
     time = Date.now();
   }
 
-  // Require the pad to already exist, like the other content API methods.
-  // Without this, sendChatMessageToPadClients -> padManager.getPad() would
-  // create the pad on demand with default content, so the documented
-  // {code:1,"padID does not exist"} result would never be returned.
-  await getPadSafe(padID, true);
+  // Reject messages addressed to a pad that doesn't exist. Without this check
+  // the downstream padManager.getPad() would create the pad on demand with
+  // default content, so the documented {code:1,"padID does not exist"} result
+  // would never be returned.
+  if (!await padManager.doesPadExists(padID)) {
+    throw new CustomError('padID does not exist', 'apierror');
+  }
 
   // save chat message to database and send message to all connected clients
   await padMessageHandler.sendChatMessageToPadClients(new ChatMessage(text, authorID, time), padID);