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>

1 files changed, 20 insertions, 11 deletions

diff --git a/frontend/src/api.js b/frontend/src/api.js
index 87ec685..a53ed90 100644
--- a/frontend/src/api.js
+++ b/frontend/src/api.js
@@ -73,7 +73,7 @@ export const api = {
    * @param {function} onEvent - Callback function for each event: (eventType, data) => void
    * @returns {Promise<void>}
    */
-  async sendMessageStream(conversationId, content, onEvent) {
+  async sendMessageStream(conversationId, content, onEvent, signal) {
     const response = await fetch(
       `${API_BASE}/api/conversations/${conversationId}/message/stream`,
       {
@@ -82,6 +82,7 @@ export const api = {
           'Content-Type': 'application/json',
         },
         body: JSON.stringify({ content }),
+        signal,
       }
     );
 
@@ -91,22 +92,30 @@ export const api = {
 
     const reader = response.body.getReader();
     const decoder = new TextDecoder();
+    let buffer = '';
 
     while (true) {
       const { done, value } = await reader.read();
       if (done) break;
 
-      const chunk = decoder.decode(value);
-      const lines = chunk.split('\n');
+      buffer += decoder.decode(value, { stream: true });
 
-      for (const line of lines) {
-        if (line.startsWith('data: ')) {
-          const data = line.slice(6);
-          try {
-            const event = JSON.parse(data);
-            onEvent(event.type, event);
-          } catch (e) {
-            console.error('Failed to parse SSE event:', e);
+      // Split on double newline (SSE event boundary)
+      const parts = buffer.split('\n\n');
+      // Last part may be incomplete — keep it in buffer
+      buffer = parts.pop();
+
+      for (const part of parts) {
+        const lines = part.split('\n');
+        for (const line of lines) {
+          if (line.startsWith('data: ')) {
+            const data = line.slice(6);
+            try {
+              const event = JSON.parse(data);
+              onEvent(event.type, event);
+            } catch (e) {
+              console.error('Failed to parse SSE event:', e);
+            }
           }
         }
       }