Add reliable widget message outbox

server.js

@@ -153,6 +153,7 @@ function initDb() {
       conversation_id INTEGER NOT NULL REFERENCES conversations(id),
       sender_type TEXT NOT NULL,
       sender_name TEXT,
+      client_message_id TEXT,
       body TEXT NOT NULL,
       created_at TEXT NOT NULL DEFAULT CURRENT_TIMESTAMP
     );
@@ -211,6 +212,8 @@ function initDb() {
     db.prepare("UPDATE visitor_sessions SET last_activity_at = last_seen_at WHERE last_activity_at IS NULL").run();
   }
   ensureColumn("conversations", "visitor_seen_at", "TEXT");
+  ensureColumn("messages", "client_message_id", "TEXT");
+  db.exec("CREATE UNIQUE INDEX IF NOT EXISTS idx_messages_client_id ON messages(conversation_id, client_message_id) WHERE client_message_id IS NOT NULL");
 }
 
 function ensureColumn(table, column, definition) {
@@ -523,6 +526,9 @@ async function createConversation(req, res) {
   if (!site) return json(res, 404, { error: "site_not_found" });
 
   const visitorToken = body.visitorToken || id("vis");
+  const clientMessageId = normalizeClientMessageId(body.clientMessageId);
+  const existingConversation = findConversationByClientMessage(site.id, visitorToken, clientMessageId);
+  if (existingConversation) return json(res, 200, conversationDetails(existingConversation));
   const publicId = id("cnv");
   const info = body.visitorInfo || {};
   const ip = clientIp(req);
@@ -552,7 +558,7 @@ async function createConversation(req, res) {
       nullish(countryFromHeaders(req))
     ).lastInsertRowid;
 
-    const messageId = insertMessage(conversationId, "visitor", info.name || "Visitor", String(body.message || "").trim());
+    const messageId = insertMessage(conversationId, "visitor", info.name || "Visitor", String(body.message || "").trim(), clientMessageId);
     saveAttachments(conversationId, messageId, body.attachments || []);
     return conversationId;
   });
@@ -570,7 +576,12 @@ async function createVisitorMessage(req, res, url) {
   if (!attachmentsAreAllowed(body.attachments || [])) return json(res, 400, { error: "only_images_allowed" });
   const conversation = findConversation(publicIdFrom(url));
   if (!conversation) return json(res, 404, { error: "conversation_not_found" });
-  const messageId = insertMessage(conversation.id, "visitor", conversation.visitor_name || "Visitor", String(body.message || "").trim());
+  const clientMessageId = normalizeClientMessageId(body.clientMessageId);
+  if (clientMessageId && messageExists(conversation.id, clientMessageId)) {
+    updateVisitorContext(conversation.id, body);
+    return json(res, 200, conversationDetails(findConversation(conversation.public_id)));
+  }
+  const messageId = insertMessage(conversation.id, "visitor", conversation.visitor_name || "Visitor", String(body.message || "").trim(), clientMessageId);
   saveAttachments(conversation.id, messageId, body.attachments || []);
   updateVisitorContext(conversation.id, body);
   markConversationUnread(conversation.id);
@@ -667,11 +678,33 @@ function publish(key, event) {
   }
 }
 
-function insertMessage(conversationId, senderType, senderName, body) {
+function insertMessage(conversationId, senderType, senderName, body, clientMessageId = null) {
   return db.prepare(`
-    INSERT INTO messages (conversation_id, sender_type, sender_name, body)
-    VALUES (?, ?, ?, ?)
-  `).run(conversationId, senderType, senderName, body).lastInsertRowid;
+    INSERT INTO messages (conversation_id, sender_type, sender_name, client_message_id, body)
+    VALUES (?, ?, ?, ?, ?)
+  `).run(conversationId, senderType, senderName, clientMessageId, body).lastInsertRowid;
+}
+
+function messageExists(conversationId, clientMessageId) {
+  return Boolean(db.prepare("SELECT 1 FROM messages WHERE conversation_id = ? AND client_message_id = ?").get(conversationId, clientMessageId));
+}
+
+function findConversationByClientMessage(siteId, visitorToken, clientMessageId) {
+  if (!clientMessageId) return null;
+  const row = db.prepare(`
+    SELECT c.public_id
+    FROM messages m
+    JOIN conversations c ON c.id = m.conversation_id
+    WHERE c.site_id = ? AND c.visitor_token = ? AND m.client_message_id = ?
+    ORDER BY m.id DESC
+    LIMIT 1
+  `).get(siteId, visitorToken, clientMessageId);
+  return row ? findConversation(row.public_id) : null;
+}
+
+function normalizeClientMessageId(value) {
+  const text = String(value || "").trim();
+  return /^[a-zA-Z0-9_-]{8,80}$/.test(text) ? text : null;
 }
 
 function saveAttachments(conversationId, messageId, attachments) {