feat: **`globals.css`** — Edit `.chat-pane`: remove `width: 3… (+7 more)

- ✅ **`globals.css`** — Edit `.chat-pane`: remove `width: 380px`, add `min-width: 0`, `overflow: hidden`, `transition: width 0.2s ease`
- ✅ **`globals.css`** — Insert `.chat-resize-handle`, `.chat-header`, `.chat-collapse-btn` rules after `.chat-pane` block
- ✅ **`globals.css`** — Append `::-webkit-scrollbar` rules at end of file
- ✅ **`ChatPane.tsx`** — Full rewrite: new props interface, header strip, conditional body, inline width style
- ✅ **`App.tsx`** — Add `chatWidth` + `chatCollapsed` state with lazy localStorage initialisers
- ✅ **`App.tsx`** — Add two `useEffect` persistence hooks
- ✅ **`App.tsx`** — Add `handleResizeMouseDown` function
- ✅ **`App.tsx`** — Update `.main-content` JSX: insert conditional resize handle div, pass new props to `<ChatPane>`

3 files changed, 169 insertions, 30 deletions

diff --git a/renderer/src/App.tsx b/renderer/src/App.tsx
index 7d75196..c3eafd4 100644
--- a/renderer/src/App.tsx
+++ b/renderer/src/App.tsx
@@ -63,15 +63,47 @@ export function App() {
     () => (localStorage.getItem("cf-theme") as Theme) ?? "dark"
   );
 
+  const [chatWidth, setChatWidth] = useState<number>(
+    () => Number(localStorage.getItem("cf-chat-width")) || 380
+  );
+  const [chatCollapsed, setChatCollapsed] = useState<boolean>(
+    () => localStorage.getItem("cf-chat-collapsed") === "true"
+  );
+
   // Keep document.documentElement in sync and persist to localStorage
   useEffect(() => {
     document.documentElement.setAttribute("data-theme", theme);
     localStorage.setItem("cf-theme", theme);
   }, [theme]);
 
+  useEffect(() => {
+    localStorage.setItem("cf-chat-width", String(chatWidth));
+  }, [chatWidth]);
+
+  useEffect(() => {
+    localStorage.setItem("cf-chat-collapsed", String(chatCollapsed));
+  }, [chatCollapsed]);
+
   const handleToggleTheme = () =>
     setTheme((t) => (t === "dark" ? "light" : "dark"));
 
+  const handleResizeMouseDown = (e: React.MouseEvent) => {
+    e.preventDefault();
+    const startX = e.clientX;
+    const startWidth = chatWidth;
+    const onMove = (ev: MouseEvent) => {
+      const delta = startX - ev.clientX; // drag left = wider chat
+      const next = Math.max(180, Math.min(700, startWidth + delta));
+      setChatWidth(next);
+    };
+    const onUp = () => {
+      document.removeEventListener("mousemove", onMove);
+      document.removeEventListener("mouseup", onUp);
+    };
+    document.addEventListener("mousemove", onMove);
+    document.addEventListener("mouseup", onUp);
+  };
+
   const hasChanges = documentContent !== originalContent;
 
   // Clear error after 5 seconds
@@ -380,6 +412,13 @@ export function App() {
           theme={theme}
         />
 
+        {!chatCollapsed && (
+          <div
+            className="chat-resize-handle"
+            onMouseDown={handleResizeMouseDown}
+          />
+        )}
+
         <ChatPane
           messages={messages}
           onSend={handleSendMessage}
@@ -390,6 +429,9 @@ export function App() {
               ? `Chat with Claude (${selectedSession.phase})...`
               : "Select a session to start"
           }
+          collapsed={chatCollapsed}
+          chatWidth={chatWidth}
+          onToggleCollapse={() => setChatCollapsed((c) => !c)}
         />
       </div>
 
diff --git a/renderer/src/components/ChatPane.tsx b/renderer/src/components/ChatPane.tsx
index 917d462..40e682c 100644
--- a/renderer/src/components/ChatPane.tsx
+++ b/renderer/src/components/ChatPane.tsx
@@ -7,6 +7,9 @@ interface ChatPaneProps {
   isLoading: boolean;
   disabled: boolean;
   placeholder: string;
+  collapsed: boolean;
+  chatWidth: number;
+  onToggleCollapse: () => void;
 }
 
 export function ChatPane({
@@ -15,6 +18,9 @@ export function ChatPane({
   isLoading,
   disabled,
   placeholder,
+  collapsed,
+  chatWidth,
+  onToggleCollapse,
 }: ChatPaneProps) {
   const [input, setInput] = useState("");
   const messagesEndRef = useRef<HTMLDivElement>(null);
@@ -30,37 +36,53 @@ export function ChatPane({
   };
 
   return (
-    <div className="chat-pane">
-      <div className="chat-messages">
-        {messages.map((msg) => (
-          <div key={msg.id} className={`message ${msg.role}`}>
-            <div className="message-content">{msg.content}</div>
-          </div>
-        ))}
-        {isLoading && (
-          <div className="message assistant loading">
-            <div className="message-content">Thinking...</div>
-          </div>
-        )}
-        <div ref={messagesEndRef} />
-      </div>
-
-      <div className="chat-input">
-        <input
-          type="text"
-          value={input}
-          onChange={(e) => setInput(e.target.value)}
-          onKeyDown={(e) => e.key === "Enter" && !e.shiftKey && handleSend()}
-          placeholder={placeholder}
-          disabled={disabled || isLoading}
-        />
-        <button
-          onClick={handleSend}
-          disabled={disabled || isLoading || !input.trim()}
-        >
-          Send
+    <div
+      className="chat-pane"
+      style={{ width: collapsed ? 28 : chatWidth }}
+    >
+      <div className="chat-header">
+        {!collapsed && <span>Chat</span>}
+        <button className="chat-collapse-btn" onClick={onToggleCollapse}>
+          {collapsed ? "⟨" : "⟩"}
         </button>
       </div>
+
+      {!collapsed && (
+        <>
+          <div className="chat-messages">
+            {messages.map((msg) => (
+              <div key={msg.id} className={`message ${msg.role}`}>
+                <div className="message-content">{msg.content}</div>
+              </div>
+            ))}
+            {isLoading && (
+              <div className="message assistant loading">
+                <div className="message-content">Thinking...</div>
+              </div>
+            )}
+            <div ref={messagesEndRef} />
+          </div>
+
+          <div className="chat-input">
+            <input
+              type="text"
+              value={input}
+              onChange={(e) => setInput(e.target.value)}
+              onKeyDown={(e) =>
+                e.key === "Enter" && !e.shiftKey && handleSend()
+              }
+              placeholder={placeholder}
+              disabled={disabled || isLoading}
+            />
+            <button
+              onClick={handleSend}
+              disabled={disabled || isLoading || !input.trim()}
+            >
+              Send
+            </button>
+          </div>
+        </>
+      )}
     </div>
   );
 }
diff --git a/renderer/src/styles/globals.css b/renderer/src/styles/globals.css
index 8e43f3a..03c7443 100644
--- a/renderer/src/styles/globals.css
+++ b/renderer/src/styles/globals.css
@@ -408,10 +408,57 @@ html[data-theme="light"] .session-rename-input {
 
 /* ── Chat Pane ───────────────────────────────────────────────── */
 .chat-pane {
-  width: 380px;
   display: flex;
   flex-direction: column;
   background: var(--bg-secondary);
+  min-width: 0;
+  overflow: hidden;
+  transition: width 0.2s ease;
+}
+
+/* ── Chat Resize Handle ──────────────────────────────────────── */
+.chat-resize-handle {
+  width: 5px;
+  background: transparent;
+  cursor: col-resize;
+  flex-shrink: 0;
+  transition: background 0.15s;
+}
+
+.chat-resize-handle:hover {
+  background: var(--accent);
+}
+
+/* ── Chat Header Strip ───────────────────────────────────────── */
+.chat-header {
+  display: flex;
+  justify-content: space-between;
+  align-items: center;
+  padding: 7px 12px;
+  background: var(--bg-secondary);
+  border-bottom: 1px solid var(--border);
+  font-size: 11px;
+  letter-spacing: 0.07em;
+  text-transform: uppercase;
+  color: var(--text-secondary);
+  flex-shrink: 0;
+}
+
+.chat-collapse-btn {
+  background: transparent;
+  border: 1px solid var(--border);
+  border-radius: 2px;
+  color: var(--text-secondary);
+  cursor: pointer;
+  font-size: 12px;
+  padding: 2px 7px;
+  font-family: inherit;
+  transition: background 0.15s, color 0.15s;
+}
+
+.chat-collapse-btn:hover {
+  background: var(--bg-tertiary);
+  color: var(--text-primary);
 }
 
 .chat-messages {
@@ -998,3 +1045,31 @@ html[data-theme="light"] .settings-textarea:focus {
   background: var(--bg-tertiary);
   color: var(--text-primary);
 }
+
+/* ── Scrollbars ──────────────────────────────────────────────── */
+.chat-messages::-webkit-scrollbar,
+.document-content::-webkit-scrollbar,
+.cm-scroller::-webkit-scrollbar {
+  width: 8px;
+  height: 8px;
+}
+
+.chat-messages::-webkit-scrollbar-track,
+.document-content::-webkit-scrollbar-track,
+.cm-scroller::-webkit-scrollbar-track {
+  background: var(--bg-primary);
+}
+
+.chat-messages::-webkit-scrollbar-thumb,
+.document-content::-webkit-scrollbar-thumb,
+.cm-scroller::-webkit-scrollbar-thumb {
+  background: var(--bg-tertiary);
+  border-radius: 4px;
+  border: 2px solid var(--bg-primary);
+}
+
+.chat-messages::-webkit-scrollbar-thumb:hover,
+.document-content::-webkit-scrollbar-thumb:hover,
+.cm-scroller::-webkit-scrollbar-thumb:hover {
+  background: var(--border);
+}