diff --git a/src/App.tsx b/src/App.tsx
index 37c1ebd..0277717 100644
--- a/src/App.tsx
+++ b/src/App.tsx
@@ -1,26 +1,33 @@
-import { useEffect } from "react";
-import { FloorPlan } from "./components/FloorPlan";
-import { HeaderBar } from "./components/HeaderBar";
-import { SidePanel } from "./components/SidePanel";
-import { setMode, startRuntime } from "./sim/runtime";
-import { loadPreferredMode, useOfficeStore } from "./store/office-store";
-
-export default function App() {
-  const theme = useOfficeStore((s) => s.theme);
-  const panelOpen = useOfficeStore((s) => s.panelOpen);
-
-  useEffect(() => {
-    startRuntime();
-    if (loadPreferredMode() === "live") setMode("live");
-  }, []);
-
-  return (
-    <div className={`app ${theme}`}>
-      <HeaderBar />
-      <div className={`main-row ${panelOpen ? "" : "panel-closed"}`}>
-        <FloorPlan />
-        {panelOpen && <SidePanel />}
-      </div>
-    </div>
-  );
-}
+import { useEffect } from "react";
+import { ChatFullscreen } from "./components/ChatFullscreen";
+import { FloorPlan } from "./components/FloorPlan";
+import { HeaderBar } from "./components/HeaderBar";
+import { SidePanel } from "./components/SidePanel";
+import { setMode, startRuntime } from "./sim/runtime";
+import { loadPreferredMode, useOfficeStore } from "./store/office-store";
+
+export default function App() {
+  const theme = useOfficeStore((s) => s.theme);
+  const panelOpen = useOfficeStore((s) => s.panelOpen);
+  const chatFullscreen = useOfficeStore((s) => s.chatFullscreen);
+  const selectedAgentId = useOfficeStore((s) => s.selectedAgentId);
+  const mode = useOfficeStore((s) => s.mode);
+
+  useEffect(() => {
+    startRuntime();
+    if (loadPreferredMode() === "live") setMode("live");
+  }, []);
+
+  const showFullscreenChat = chatFullscreen && mode === "live" && selectedAgentId !== null;
+
+  return (
+    <div className={`app ${theme}`}>
+      <HeaderBar />
+      <div className={`main-row ${panelOpen ? "" : "panel-closed"}`}>
+        <FloorPlan />
+        {panelOpen && <SidePanel />}
+      </div>
+      {showFullscreenChat && <ChatFullscreen />}
+    </div>
+  );
+}
diff --git a/src/components/ChatConversation.tsx b/src/components/ChatConversation.tsx
new file mode 100644
index 0000000..0c1c9a0
--- /dev/null
+++ b/src/components/ChatConversation.tsx
@@ -0,0 +1,109 @@
+import { useEffect, useRef, useState } from "react";
+import { useOfficeStore } from "@/store/office-store";
+import { resetChat, sendChat } from "@/gateway/live";
+
+/**
+ * Two-way chat with one project — each message runs headless and is stitched
+ * to the previous with --resume. Shared by the side panel and the full-screen
+ * overlay via the `variant` prop.
+ */
+export function ChatConversation({
+  agentId,
+  variant,
+}: {
+  agentId: string;
+  variant: "panel" | "full";
+}) {
+  const thread = useOfficeStore((s) => s.chats.get(agentId));
+  const setChatFullscreen = useOfficeStore((s) => s.setChatFullscreen);
+  const isFull = useOfficeStore((s) => s.chatFullscreen);
+  const [input, setInput] = useState("");
+  const [fromProject, setFromProject] = useState(false);
+  const listRef = useRef<HTMLDivElement>(null);
+
+  const busy = thread?.busy ?? false;
+  const messages = thread?.messages ?? [];
+  const started = messages.length > 0;
+
+  useEffect(() => {
+    listRef.current?.scrollTo({ top: listRef.current.scrollHeight });
+  }, [messages.length, busy]);
+
+  const send = () => {
+    const text = input.trim();
+    if (!text || busy) return;
+    sendChat(agentId, text, fromProject);
+    setInput("");
+  };
+
+  return (
+    <div className={`chat-panel ${variant === "full" ? "chat-panel-full" : ""}`}>
+      <div className="chat-head">
+        <h3>對話</h3>
+        <div className="chat-head-actions">
+          {started && (
+            <button className="link-btn" onClick={() => resetChat(agentId)} disabled={busy}>
+              🔄 新對話
+            </button>
+          )}
+          <button
+            className="link-btn"
+            onClick={() => setChatFullscreen(!isFull)}
+            title={isFull ? "縮回側邊面板" : "全螢幕對話"}
+          >
+            {isFull ? "⊟ 縮小" : "⛶ 全螢幕"}
+          </button>
+        </div>
+      </div>
+
+      {started && (
+        <div className="chat-list" ref={listRef}>
+          {messages.map((m, i) => (
+            <div key={i} className={`chat-msg ${m.role}`}>
+              {m.text}
+            </div>
+          ))}
+          {busy && <div className="chat-msg pending">⋯ 執行中,過程看辦公室裡的小人</div>}
+        </div>
+      )}
+
+      <textarea
+        value={input}
+        onChange={(e) => setInput(e.target.value)}
+        placeholder={started ? "繼續對話…(Enter 送出)" : "跟這個專案的 Codex 對話…(Enter 送出)"}
+        rows={variant === "full" ? 3 : 2}
+        onKeyDown={(e) => {
+          if (e.key === "Enter" && !e.shiftKey) {
+            e.preventDefault();
+            send();
+          }
+        }}
+      />
+      <div className="task-composer-row">
+        {!started ? (
+          <label
+            className="tip"
+            data-tip="第一句話從該專案最近一段「已結束」的 session 接續(codex exec resume)。注意:無法插入正在終端機進行中的互動對話。"
+          >
+            <input
+              type="checkbox"
+              checked={fromProject}
+              onChange={(e) => setFromProject(e.target.checked)}
+            />
+            接續專案最近 session
+          </label>
+        ) : (
+          <span
+            className="chat-hint tip"
+            data-tip="辦公室對話有自己的 session,每則訊息自動以 --resume 延續,每則訊息逐則接力。"
+          >
+            ✓ 對話自動延續
+          </span>
+        )}
+        <button className="btn assign-btn" onClick={send} disabled={busy || !input.trim()}>
+          {busy ? "執行中…" : "送出"}
+        </button>
+      </div>
+    </div>
+  );
+}
diff --git a/src/components/ChatFullscreen.tsx b/src/components/ChatFullscreen.tsx
new file mode 100644
index 0000000..dedec73
--- /dev/null
+++ b/src/components/ChatFullscreen.tsx
@@ -0,0 +1,54 @@
+import { useEffect } from "react";
+import { STATUS_COLORS, STATUS_LABELS } from "@/lib/constants";
+import { generateAppearance } from "@/lib/appearance";
+import { useOfficeStore } from "@/store/office-store";
+import { ChatConversation } from "./ChatConversation";
+import { Pawn } from "./Pawn";
+
+/** Full-screen chat overlay for the selected project agent. */
+export function ChatFullscreen() {
+  const agent = useOfficeStore((s) => (s.selectedAgentId ? s.agents.get(s.selectedAgentId) : undefined));
+  const setChatFullscreen = useOfficeStore((s) => s.setChatFullscreen);
+
+  // Esc returns to the office.
+  useEffect(() => {
+    const onKey = (e: KeyboardEvent) => {
+      if (e.key === "Escape") setChatFullscreen(false);
+    };
+    window.addEventListener("keydown", onKey);
+    return () => window.removeEventListener("keydown", onKey);
+  }, [setChatFullscreen]);
+
+  if (!agent) return null;
+
+  return (
+    <div className="chat-full-overlay">
+      <div className="chat-full-card">
+        <div className="chat-full-topbar">
+          <div className="chat-full-who">
+            <svg viewBox="-30 -42 60 68" width="42" height="48">
+              <Pawn appearance={generateAppearance(agent.id)} pose="stand" motion="none" />
+            </svg>
+            <div>
+              <h2>{agent.name}</h2>
+              <span
+                className="status-chip"
+                style={{
+                  backgroundColor: `${STATUS_COLORS[agent.status]}22`,
+                  color: STATUS_COLORS[agent.status],
+                }}
+              >
+                ● {STATUS_LABELS[agent.status]}
+              </span>
+              <code className="model-tag">{agent.model}</code>
+            </div>
+          </div>
+          <button className="btn" onClick={() => setChatFullscreen(false)} title="縮回辦公室 (Esc)">
+            ⊟ 回到辦公室
+          </button>
+        </div>
+        <ChatConversation agentId={agent.id} variant="full" />
+      </div>
+    </div>
+  );
+}
diff --git a/src/components/SidePanel.tsx b/src/components/SidePanel.tsx
index 773acdf..b50112e 100644
--- a/src/components/SidePanel.tsx
+++ b/src/components/SidePanel.tsx
@@ -1,98 +1,12 @@
-import { useEffect, useRef, useState } from "react";
 import { STATUS_COLORS, STATUS_LABELS } from "@/lib/constants";
 import { generateAppearance } from "@/lib/appearance";
 import { useOfficeStore } from "@/store/office-store";
 import { getDirector } from "@/sim/runtime";
-import { resetChat, sendChat } from "@/gateway/live";
+import { ChatConversation } from "./ChatConversation";
 import { Pawn } from "./Pawn";
 
 const ROLE_LABELS = { lead: "Lead Agent", agent: "Agent", subagent: "Subagent" } as const;
 
-/** LIVE mode: two-way chat with this project — each message runs headless, stitched with --resume. */
-function ChatPanel({ agentId }: { agentId: string }) {
-  const thread = useOfficeStore((s) => s.chats.get(agentId));
-  const [input, setInput] = useState("");
-  const [fromProject, setFromProject] = useState(false);
-  const listRef = useRef<HTMLDivElement>(null);
-
-  const busy = thread?.busy ?? false;
-  const messages = thread?.messages ?? [];
-  const started = messages.length > 0;
-
-  useEffect(() => {
-    listRef.current?.scrollTo({ top: listRef.current.scrollHeight });
-  }, [messages.length, busy]);
-
-  const send = () => {
-    const text = input.trim();
-    if (!text || busy) return;
-    sendChat(agentId, text, fromProject);
-    setInput("");
-  };
-
-  return (
-    <div className="chat-panel">
-      <div className="chat-head">
-        <h3>對話</h3>
-        {started && (
-          <button className="link-btn" onClick={() => resetChat(agentId)} disabled={busy}>
-            🔄 新對話
-          </button>
-        )}
-      </div>
-
-      {started && (
-        <div className="chat-list" ref={listRef}>
-          {messages.map((m, i) => (
-            <div key={i} className={`chat-msg ${m.role}`}>
-              {m.text}
-            </div>
-          ))}
-          {busy && <div className="chat-msg pending">⋯ 執行中,過程看辦公室裡的小人</div>}
-        </div>
-      )}
-
-      <textarea
-        value={input}
-        onChange={(e) => setInput(e.target.value)}
-        placeholder={started ? "繼續對話…(Enter 送出)" : "跟這個專案的 Codex 對話…(Enter 送出)"}
-        rows={2}
-        onKeyDown={(e) => {
-          if (e.key === "Enter" && !e.shiftKey) {
-            e.preventDefault();
-            send();
-          }
-        }}
-      />
-      <div className="task-composer-row">
-        {!started ? (
-          <label
-            className="tip"
-            data-tip="第一句話從該專案最近一段「已結束」的 session 接續(codex exec resume)。注意:無法插入正在終端機進行中的互動對話。"
-          >
-            <input
-              type="checkbox"
-              checked={fromProject}
-              onChange={(e) => setFromProject(e.target.checked)}
-            />
-            接續專案最近 session
-          </label>
-        ) : (
-          <span
-            className="chat-hint tip"
-            data-tip="辦公室對話有自己的 session,每則訊息自動以 --resume 延續,每則訊息逐則接力。"
-          >
-            ✓ 對話自動延續
-          </span>
-        )}
-        <button className="btn assign-btn" onClick={send} disabled={busy || !input.trim()}>
-          {busy ? "執行中…" : "送出"}
-        </button>
-      </div>
-    </div>
-  );
-}
-
 export function SidePanel() {
   const selectedAgentId = useOfficeStore((s) => s.selectedAgentId);
   const agent = useOfficeStore((s) => (s.selectedAgentId ? s.agents.get(s.selectedAgentId) : undefined));
@@ -186,7 +100,9 @@ export function SidePanel() {
             </button>
           )}
 
-          {agent.role !== "subagent" && mode === "live" && <ChatPanel agentId={agent.id} />}
+          {agent.role !== "subagent" && mode === "live" && (
+            <ChatConversation agentId={agent.id} variant="panel" />
+          )}
         </div>
       ) : (
         <div className="panel-hint">
diff --git a/src/store/office-store.ts b/src/store/office-store.ts
index c92c74b..9d9d112 100644
--- a/src/store/office-store.ts
+++ b/src/store/office-store.ts
@@ -38,6 +38,8 @@ interface OfficeState {
   mode: "sim" | "live";
   /** side panel visibility (collapse to maximise the office view) */
   panelOpen: boolean;
+  /** LIVE-mode chat expanded to a full-screen overlay */
+  chatFullscreen: boolean;
   /** simulation clock, seconds */
   clock: number;
 
@@ -47,6 +49,7 @@ interface OfficeState {
   setSpeed: (s: number) => void;
   setMode: (m: "sim" | "live") => void;
   togglePanel: () => void;
+  setChatFullscreen: (v: boolean) => void;
   clearWorld: () => void;
 
   chatAppend: (agentId: string, msg: ChatMessage) => void;
@@ -124,9 +127,10 @@ export const useOfficeStore = create<OfficeState>()((set, get) => ({
   speed: 1,
   mode: "sim",
   panelOpen: savedPanel !== "0",
+  chatFullscreen: false,
   clock: 0,
 
-  selectAgent: (id) => set({ selectedAgentId: id }),
+  selectAgent: (id) => set({ selectedAgentId: id, chatFullscreen: id === null ? false : get().chatFullscreen }),
   setTheme: (t) => {
     savePref("office-theme", t);
     set({ theme: t });
@@ -142,6 +146,7 @@ export const useOfficeStore = create<OfficeState>()((set, get) => ({
       savePref("office-panel", state.panelOpen ? "0" : "1");
       return { panelOpen: !state.panelOpen };
     }),
+  setChatFullscreen: (v) => set({ chatFullscreen: v }),
   clearWorld: () =>
     set({
       agents: new Map(),
@@ -150,6 +155,7 @@ export const useOfficeStore = create<OfficeState>()((set, get) => ({
       events: [],
       chats: new Map(),
       selectedAgentId: null,
+      chatFullscreen: false,
     }),
 
   chatAppend: (agentId, msg) =>
diff --git a/src/styles.css b/src/styles.css
index 840133d..f4fb188 100644
--- a/src/styles.css
+++ b/src/styles.css
@@ -372,7 +372,88 @@
   cursor: default;
 }
 
-.chat-list {
+.chat-head-actions {
+  display: flex;
+  align-items: center;
+  gap: 12px;
+}
+
+.chat-head .link-btn:disabled {
+  opacity: 0.4;
+  cursor: default;
+}
+
+/* ── full-screen chat overlay ── */
+
+.chat-full-overlay {
+  position: fixed;
+  inset: 0;
+  z-index: 60;
+  background: color-mix(in srgb, var(--bg) 82%, transparent);
+  backdrop-filter: blur(6px);
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  padding: 24px;
+  animation: card-in 0.2s ease-out;
+}
+
+.chat-full-card {
+  width: min(860px, 100%);
+  height: min(88vh, 900px);
+  display: flex;
+  flex-direction: column;
+  background: var(--bg-panel);
+  border: 1px solid var(--border);
+  border-radius: 16px;
+  box-shadow: 0 20px 60px rgba(0, 0, 0, 0.35);
+  overflow: hidden;
+  padding: 18px 20px 20px;
+}
+
+.chat-full-topbar {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 12px;
+  padding-bottom: 14px;
+  border-bottom: 1px solid var(--border);
+}
+
+.chat-full-who {
+  display: flex;
+  align-items: center;
+  gap: 12px;
+}
+
+.chat-full-who svg {
+  background: var(--bg-card);
+  border: 1px solid var(--border);
+  border-radius: 10px;
+  flex-shrink: 0;
+}
+
+.chat-full-who h2 {
+  font-family: "Sora", system-ui, sans-serif;
+  font-size: 20px;
+  font-weight: 600;
+  margin-bottom: 4px;
+}
+
+.chat-full-who .model-tag {
+  margin-left: 8px;
+}
+
+/* the shared conversation fills the full-screen card */
+.chat-panel-full {
+  flex: 1;
+  min-height: 0;
+  display: flex;
+  flex-direction: column;
+  margin-top: 14px;
+}
+
+.chat-panel-full .chat-list {
   display: flex;
   flex-direction: column;
   gap: 6px;