diff --git a/src/page/workspace/workplan/chat-conversation.tsx b/src/page/workspace/workplan/chat-conversation.tsx
index d7917b2..b70dc68 100644
--- a/src/page/workspace/workplan/chat-conversation.tsx
+++ b/src/page/workspace/workplan/chat-conversation.tsx
@@ -22,11 +22,15 @@ import type {
 } from "./chat/types";
 import { EMPTY_STREAM } from "./chat/types";
 import { ModelSelectorPopover } from "./chat/model-selector-popover";
+import { RepoMentionPopover } from "./chat/repo-mention-popover";
 import { MessageBubble } from "./chat/message-bubble";
 import { StreamingView } from "./chat/streaming-view";
 import { CodePreviewProvider } from "./chat/code-preview-context";
 import { CodePreviewPanel } from "./chat/code-preview-panel";
 import { MessageNavDots } from "./chat/message-nav-dots";
+import { mentionAtCursor } from "@/components/ai-elements/mention-textarea-overlay";
+import { extractMentions } from "@/lib/ir/parser";
+import { MentionChip } from "@/lib/ir/mention-chip";
 
 // ---- Helpers ----
 
@@ -514,6 +518,28 @@ function ChatInner({
 
   const handleKeyDown = useCallback(
     (e: React.KeyboardEvent<HTMLTextAreaElement>) => {
+      // ---- Mention-aware backspace ----
+      if (e.key === "Backspace") {
+        const ta = e.currentTarget;
+        const { selectionStart, selectionEnd } = ta;
+        if (selectionStart === selectionEnd && selectionStart > 0) {
+          const hit = mentionAtCursor(textInput.value, selectionStart);
+          if (hit) {
+            e.preventDefault();
+            const newText =
+              textInput.value.slice(0, hit.start) +
+              textInput.value.slice(hit.end);
+            textInput.setInput(newText);
+            // Restore cursor to the position where the mention was.
+            requestAnimationFrame(() => {
+              ta.selectionStart = ta.selectionEnd = hit.start;
+            });
+            return;
+          }
+        }
+      }
+
+      // ---- Enter to submit ----
       if (e.key === "Enter" && !e.shiftKey && !sending) {
         e.preventDefault();
         const text = textInput.value;
@@ -546,7 +572,7 @@ function ChatInner({
             <Sparkles className="size-3 text-primary/70" />
           </div>
           <h1 className="truncate text-sm font-semibold text-foreground">
-            {conversation?.title ?? "Loading..."}
+            {conversation?.title && conversation.title.trim().length > 2 ? conversation.title : "New conversation"}
           </h1>
         </div>
       </header>
@@ -626,6 +652,35 @@ function ChatInner({
       {/* Composer */}
       <footer className="shrink-0 border-t border-border/60 bg-card/70 backdrop-blur-md">
         <div className="mx-auto max-w-3xl px-4 py-3">
+          {/* Repo mention popover — positioned above the input */}
+          <div className="relative">
+            <RepoMentionPopover
+              workspaceName={projectName}
+              textValue={textInput.value}
+              onInsertMention={(mentionText, replaceFrom, replaceTo) => {
+                const before = textInput.value.slice(0, replaceFrom);
+                const after = textInput.value.slice(replaceTo);
+                textInput.setInput(before + mentionText + after);
+              }}
+            />
+          </div>
+          {/* Active mention chips — shows which repos are referenced */}
+          {(() => {
+            const mentions = extractMentions(textInput.value);
+            if (mentions.length === 0) return null;
+            return (
+              <div className="mb-1.5 flex flex-wrap gap-1.5">
+                {mentions.map((m, i) => (
+                  <MentionChip
+                    key={`${m.entityId}-${i}`}
+                    entityType={m.entityType}
+                    entityId={m.entityId}
+                    entityLabel={m.entityLabel}
+                  />
+                ))}
+              </div>
+            );
+          })()}
           <PromptInput
             globalDrop={false}
             onSubmit={({ text }) => handleSubmit(text)}
@@ -633,7 +688,7 @@ function ChatInner({
             <PromptInputBody>
               <PromptInputTextarea
                 className="min-h-[48px] max-h-[200px] resize-none rounded-xl border-border/60 bg-muted/40 text-sm shadow-inner transition-colors focus-visible:bg-background focus-visible:ring-1 focus-visible:ring-primary/20"
-                placeholder="Type a message…"
+                placeholder="Type a message… (use @ to mention a repo)"
                 onKeyDown={handleKeyDown}
               />
             </PromptInputBody>
diff --git a/src/page/workspace/workplan/chat-sidebar.tsx b/src/page/workspace/workplan/chat-sidebar.tsx
index 9c2f035..0b181bc 100644
--- a/src/page/workspace/workplan/chat-sidebar.tsx
+++ b/src/page/workspace/workplan/chat-sidebar.tsx
@@ -152,7 +152,7 @@ export function WorkplanChatSidebar() {
             <MessageSquare className="size-3.5 text-primary/70" />
           </div>
           <span className="text-xs font-semibold uppercase tracking-[0.06em] text-muted-foreground">
-            AI Chats
+            Chats
           </span>
         </div>
         <motion.button
diff --git a/src/page/workspace/workplan/chat/message-bubble.tsx b/src/page/workspace/workplan/chat/message-bubble.tsx
index 27197a4..4a9a12c 100644
--- a/src/page/workspace/workplan/chat/message-bubble.tsx
+++ b/src/page/workspace/workplan/chat/message-bubble.tsx
@@ -1,5 +1,5 @@
 import { memo } from "react";
-import { User, Sparkles } from "lucide-react";
+import { User, Sparkles, AlertTriangle } from "lucide-react";
 import { cn } from "@/lib/utils";
 import {
   Reasoning,
@@ -7,6 +7,7 @@ import {
   ReasoningContent,
 } from "@/components/ai-elements/reasoning";
 import { MarkdownRenderer } from "@/components/MarkdownRenderer";
+import { MentionRenderer } from "@/lib/ir/mention-renderer";
 import { getProviderIcon } from "./provider-icon";
 import { isVisibleToolCall } from "./tool-utils";
 import { ToolCallList } from "./tool-call-list";
@@ -28,6 +29,7 @@ export const MessageBubble = memo(function MessageBubble({
     !isUser &&
     msg.tool_calls &&
     msg.tool_calls.some((tc) => isVisibleToolCall(tc.name));
+  const isError = !isUser && /^Error:|I encountered an error/i.test(msg.content);
 
   return (
     <div
@@ -55,11 +57,30 @@ export const MessageBubble = memo(function MessageBubble({
             "relative overflow-hidden text-sm leading-relaxed shadow-sm",
             isUser
               ? "rounded-2xl rounded-tr-sm bg-primary text-primary-foreground px-4 py-2.5"
-              : "rounded-2xl rounded-tl-sm bg-muted/70 text-foreground border border-border/40 px-4 py-2.5",
+              : isError
+                ? "rounded-2xl rounded-tl-sm bg-destructive/[0.06] text-foreground border border-destructive/20 px-4 py-2.5"
+                : "rounded-2xl rounded-tl-sm bg-muted/70 text-foreground border border-border/40 px-4 py-2.5",
           )}
         >
           {isUser ? (
-            <div className="whitespace-pre-wrap break-words">{msg.content}</div>
+            <div className="whitespace-pre-wrap break-words">
+              <MentionRenderer content={msg.content} />
+            </div>
+          ) : isError ? (
+            <div className="flex items-start gap-2.5">
+              <AlertTriangle className="mt-0.5 size-4 shrink-0 text-destructive/60" />
+              <div className="min-w-0 flex-1">
+                <p className="text-[13px] font-medium text-destructive/80">Something went wrong</p>
+                <div className="mt-1 text-destructive/60">
+                  <MarkdownRenderer
+                    content={msg.content.replace(/^(Error:\s*|I encountered an error while processing your request:\s*)/i, "")}
+                    onOpenCodePanel={(payload) =>
+                      openCodePreview({ ...payload, id: crypto.randomUUID() })
+                    }
+                  />
+                </div>
+              </div>
+            </div>
           ) : (
             <MarkdownRenderer
               content={msg.content}
diff --git a/src/page/workspace/workplan/chat/utils.ts b/src/page/workspace/workplan/chat/utils.ts
index 2e7a54d..35cbe9b 100644
--- a/src/page/workspace/workplan/chat/utils.ts
+++ b/src/page/workspace/workplan/chat/utils.ts
@@ -16,6 +16,8 @@ export function formatTime(iso: string | null | undefined): string {
 }
 
 export function truncateTitle(title: string): string {
-  if (title.length <= MAX_TITLE_LENGTH) return title;
-  return title.slice(0, MAX_TITLE_LENGTH) + "\u2026";
+  const trimmed = title.trim();
+  if (!trimmed || trimmed.length <= 2) return "New conversation";
+  if (trimmed.length <= MAX_TITLE_LENGTH) return trimmed;
+  return trimmed.slice(0, MAX_TITLE_LENGTH) + "\u2026";
 }