Multi-turn conversation, stop generation, SSE fix, and UI improvements

- Multi-turn context: all council stages now receive conversation history
  (user messages + Stage 3 chairman responses) for coherent follow-ups
- Stop generation: abort streaming mid-request, recover query to input box
- SSE parsing: buffer-based chunking to prevent JSON split across packets
- Atomic storage: user + assistant messages saved together after completion,
  preventing dangling messages on abort
- GFM markdown: tables, strikethrough via remark-gfm plugin + table styles
- Performance: memo user messages and completed assistant messages, only
  re-render the active streaming message
- Model config: gpt-5.2, claude-opus-4.6 as chairman
- Always show input box for multi-turn conversations

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

5 files changed, 133 insertions, 70 deletions

diff --git a/frontend/src/components/ChatInterface.css b/frontend/src/components/ChatInterface.css
index 0d01300..63bc75d 100644
--- a/frontend/src/components/ChatInterface.css
+++ b/frontend/src/components/ChatInterface.css
@@ -161,3 +161,22 @@
   background: #ccc;
   border-color: #ccc;
 }
+
+.stop-button {
+  padding: 14px 28px;
+  background: #e24a4a;
+  border: 1px solid #e24a4a;
+  border-radius: 8px;
+  color: #fff;
+  font-size: 15px;
+  font-weight: 600;
+  cursor: pointer;
+  transition: background 0.2s;
+  white-space: nowrap;
+  align-self: flex-end;
+}
+
+.stop-button:hover {
+  background: #c93636;
+  border-color: #c93636;
+}
diff --git a/frontend/src/components/ChatInterface.jsx b/frontend/src/components/ChatInterface.jsx
index 3ae796c..5f431c2 100644
--- a/frontend/src/components/ChatInterface.jsx
+++ b/frontend/src/components/ChatInterface.jsx
@@ -1,25 +1,102 @@
-import { useState, useEffect, useRef } from 'react';
+import { useState, useEffect, useRef, memo } from 'react';
 import ReactMarkdown from 'react-markdown';
+import remarkGfm from 'remark-gfm';
 import Stage1 from './Stage1';
 import Stage2 from './Stage2';
 import Stage3 from './Stage3';
 import './ChatInterface.css';
 
+const remarkPlugins = [remarkGfm];
+
+// Only memoize user messages (they never change once sent)
+const UserMessage = memo(function UserMessage({ content }) {
+  return (
+    <div className="message-group">
+      <div className="user-message">
+        <div className="message-label">You</div>
+        <div className="message-content">
+          <div className="markdown-content">
+            <ReactMarkdown remarkPlugins={remarkPlugins}>{content}</ReactMarkdown>
+          </div>
+        </div>
+      </div>
+    </div>
+  );
+});
+
+// Memoize completed assistant messages, but skip memo for the active (last) one
+const AssistantMessage = memo(function AssistantMessage({ msg, isActive }) {
+  return (
+    <div className="message-group">
+      <div className="assistant-message">
+        <div className="message-label">LLM Council</div>
+
+        {/* Stage 1 */}
+        {msg.loading?.stage1 && (
+          <div className="stage-loading">
+            <div className="spinner"></div>
+            <span>Running Stage 1: Collecting individual responses...</span>
+          </div>
+        )}
+        {msg.stage1 && <Stage1 responses={msg.stage1} />}
+
+        {/* Stage 2 */}
+        {msg.loading?.stage2 && (
+          <div className="stage-loading">
+            <div className="spinner"></div>
+            <span>Running Stage 2: Peer rankings...</span>
+          </div>
+        )}
+        {msg.stage2 && (
+          <Stage2
+            rankings={msg.stage2}
+            labelToModel={msg.metadata?.label_to_model}
+            aggregateRankings={msg.metadata?.aggregate_rankings}
+          />
+        )}
+
+        {/* Stage 3 */}
+        {msg.loading?.stage3 && (
+          <div className="stage-loading">
+            <div className="spinner"></div>
+            <span>Running Stage 3: Final synthesis...</span>
+          </div>
+        )}
+        {msg.stage3 && <Stage3 finalResponse={msg.stage3} />}
+      </div>
+    </div>
+  );
+}, (prevProps, nextProps) => {
+  // If active (streaming), always re-render
+  if (prevProps.isActive || nextProps.isActive) return false;
+  // Otherwise skip re-render (completed messages don't change)
+  return true;
+});
+
 export default function ChatInterface({
   conversation,
   onSendMessage,
+  onStopGeneration,
   isLoading,
+  pendingInput,
+  onPendingInputConsumed,
 }) {
   const [input, setInput] = useState('');
+  const textareaRef = useRef(null);
   const messagesEndRef = useRef(null);
 
-  const scrollToBottom = () => {
+  useEffect(() => {
     messagesEndRef.current?.scrollIntoView({ behavior: 'smooth' });
-  };
+  }, [conversation, isLoading]);
 
+  // Recover input from stopped generation
   useEffect(() => {
-    scrollToBottom();
-  }, [conversation]);
+    if (pendingInput !== null) {
+      setInput(pendingInput);
+      onPendingInputConsumed();
+      setTimeout(() => textareaRef.current?.focus(), 0);
+    }
+  }, [pendingInput]);
 
   const handleSubmit = (e) => {
     e.preventDefault();
@@ -30,7 +107,6 @@ export default function ChatInterface({
   };
 
   const handleKeyDown = (e) => {
-    // Submit on Enter (without Shift)
     if (e.key === 'Enter' && !e.shiftKey) {
       e.preventDefault();
       handleSubmit(e);
@@ -57,57 +133,13 @@ export default function ChatInterface({
             <p>Ask a question to consult the LLM Council</p>
           </div>
         ) : (
-          conversation.messages.map((msg, index) => (
-            <div key={index} className="message-group">
-              {msg.role === 'user' ? (
-                <div className="user-message">
-                  <div className="message-label">You</div>
-                  <div className="message-content">
-                    <div className="markdown-content">
-                      <ReactMarkdown>{msg.content}</ReactMarkdown>
-                    </div>
-                  </div>
-                </div>
-              ) : (
-                <div className="assistant-message">
-                  <div className="message-label">LLM Council</div>
-
-                  {/* Stage 1 */}
-                  {msg.loading?.stage1 && (
-                    <div className="stage-loading">
-                      <div className="spinner"></div>
-                      <span>Running Stage 1: Collecting individual responses...</span>
-                    </div>
-                  )}
-                  {msg.stage1 && <Stage1 responses={msg.stage1} />}
-
-                  {/* Stage 2 */}
-                  {msg.loading?.stage2 && (
-                    <div className="stage-loading">
-                      <div className="spinner"></div>
-                      <span>Running Stage 2: Peer rankings...</span>
-                    </div>
-                  )}
-                  {msg.stage2 && (
-                    <Stage2
-                      rankings={msg.stage2}
-                      labelToModel={msg.metadata?.label_to_model}
-                      aggregateRankings={msg.metadata?.aggregate_rankings}
-                    />
-                  )}
-
-                  {/* Stage 3 */}
-                  {msg.loading?.stage3 && (
-                    <div className="stage-loading">
-                      <div className="spinner"></div>
-                      <span>Running Stage 3: Final synthesis...</span>
-                    </div>
-                  )}
-                  {msg.stage3 && <Stage3 finalResponse={msg.stage3} />}
-                </div>
-              )}
-            </div>
-          ))
+          conversation.messages.map((msg, index) => {
+            if (msg.role === 'user') {
+              return <UserMessage key={index} content={msg.content} />;
+            }
+            const isLastAssistant = isLoading && index === conversation.messages.length - 1;
+            return <AssistantMessage key={index} msg={msg} isActive={isLastAssistant} />;
+          })
         )}
 
         {isLoading && (
@@ -120,9 +152,9 @@ export default function ChatInterface({
         <div ref={messagesEndRef} />
       </div>
 
-      {conversation.messages.length === 0 && (
-        <form className="input-form" onSubmit={handleSubmit}>
+      <form className="input-form" onSubmit={handleSubmit}>
           <textarea
+            ref={textareaRef}
             className="message-input"
             placeholder="Ask your question... (Shift+Enter for new line, Enter to send)"
             value={input}
@@ -131,15 +163,24 @@ export default function ChatInterface({
             disabled={isLoading}
             rows={3}
           />
-          <button
-            type="submit"
-            className="send-button"
-            disabled={!input.trim() || isLoading}
-          >
-            Send
-          </button>
+          {isLoading ? (
+            <button
+              type="button"
+              className="stop-button"
+              onClick={onStopGeneration}
+            >
+              Stop
+            </button>
+          ) : (
+            <button
+              type="submit"
+              className="send-button"
+              disabled={!input.trim()}
+            >
+              Send
+            </button>
+          )}
         </form>
-      )}
     </div>
   );
 }
diff --git a/frontend/src/components/Stage1.jsx b/frontend/src/components/Stage1.jsx
index 071937c..7478876 100644
--- a/frontend/src/components/Stage1.jsx
+++ b/frontend/src/components/Stage1.jsx
@@ -1,5 +1,6 @@
 import { useState } from 'react';
 import ReactMarkdown from 'react-markdown';
+import remarkGfm from 'remark-gfm';
 import './Stage1.css';
 
 export default function Stage1({ responses }) {
@@ -28,7 +29,7 @@ export default function Stage1({ responses }) {
       <div className="tab-content">
         <div className="model-name">{responses[activeTab].model}</div>
         <div className="response-text markdown-content">
-          <ReactMarkdown>{responses[activeTab].response}</ReactMarkdown>
+          <ReactMarkdown remarkPlugins={[remarkGfm]}>{responses[activeTab].response}</ReactMarkdown>
         </div>
       </div>
     </div>
diff --git a/frontend/src/components/Stage2.jsx b/frontend/src/components/Stage2.jsx
index 2550fa6..5d28ed7 100644
--- a/frontend/src/components/Stage2.jsx
+++ b/frontend/src/components/Stage2.jsx
@@ -1,5 +1,6 @@
 import { useState } from 'react';
 import ReactMarkdown from 'react-markdown';
+import remarkGfm from 'remark-gfm';
 import './Stage2.css';
 
 function deAnonymizeText(text, labelToModel) {
@@ -48,7 +49,7 @@ export default function Stage2({ rankings, labelToModel, aggregateRankings }) {
           {rankings[activeTab].model}
         </div>
         <div className="ranking-content markdown-content">
-          <ReactMarkdown>
+          <ReactMarkdown remarkPlugins={[remarkGfm]}>
             {deAnonymizeText(rankings[activeTab].ranking, labelToModel)}
           </ReactMarkdown>
         </div>
diff --git a/frontend/src/components/Stage3.jsx b/frontend/src/components/Stage3.jsx
index 9a9dbf7..f63a442 100644
--- a/frontend/src/components/Stage3.jsx
+++ b/frontend/src/components/Stage3.jsx
@@ -1,4 +1,5 @@
 import ReactMarkdown from 'react-markdown';
+import remarkGfm from 'remark-gfm';
 import './Stage3.css';
 
 export default function Stage3({ finalResponse }) {
@@ -14,7 +15,7 @@ export default function Stage3({ finalResponse }) {
           Chairman: {finalResponse.model.split('/')[1] || finalResponse.model}
         </div>
         <div className="final-text markdown-content">
-          <ReactMarkdown>{finalResponse.response}</ReactMarkdown>
+          <ReactMarkdown remarkPlugins={[remarkGfm]}>{finalResponse.response}</ReactMarkdown>
         </div>
       </div>
     </div>