add generation cancellation middleware and refactor chat/message workflows to support HTTP client disconnections

public/js/script.js

@@ -496,6 +496,7 @@ async function editChatMessage(messageId, fallbackIndex = -1) {
     const target = await resolveMessageTarget(messageId, fallbackIndex);
     if (!target) return setNotice("Message is not ready yet. Try again.", "error");
     const { index, message } = target;
+    const sourceChatId = conversation.activeChatId;
     const nextContent = await promptPopup({
         eyebrow: message.role === "user" ? "Your message" : "Assistant message",
         title: "Edit message",
@@ -513,8 +514,8 @@ async function editChatMessage(messageId, fallbackIndex = -1) {
             description: "This creates a new chat from the messages before this one and sends your edited message there. The original chat stays unchanged.",
             confirmLabel: "Create branch"
         });
-        if (!confirmed) return;
-        const sourceChatId = conversation.activeChatId;
+        if (!confirmed || conversation.isProcessing) return;
+        conversation.regenerationChatId = sourceChatId;
         setLoadingState(true, {
             eyebrow: "Branching",
             title: "Editing and resending",
@@ -526,11 +527,12 @@ async function editChatMessage(messageId, fallbackIndex = -1) {
                 message: content,
                 model: modelSelect.value,
                 confirmed: true
-            });
+            }, {timeoutMs: 660000});
             if (res.error) return setNotice(res.error, "error");
-            await openCreatedChat(res.chat);
-            return setNotice("Created and opened the edited chat branch.", "success");
+            if (conversation.activeChatId === sourceChatId) await openCreatedChat(res.chat);
+            return setNotice("Created the edited chat branch.", "success");
         } finally {
+            conversation.regenerationChatId = null;
             setLoadingState(false);
         }
     }