feat(08-01): create JKSessionChatWindow with WindowPortal integration

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

jam-ui/src/components/client/JKSessionChatWindow.js

@@ -0,0 +1,75 @@
+import React, { useCallback } from 'react';
+import { useSelector, useDispatch } from 'react-redux';
+import WindowPortal from '../common/WindowPortal.js';
+import JKChatHeader from './chat/JKChatHeader.js';
+import {
+  selectIsChatWindowOpen,
+  selectActiveChannel,
+  closeChatWindow
+} from '../../store/features/sessionChatSlice';
+
+/**
+ * JKSessionChatWindow - Main chat window component with WindowPortal integration
+ *
+ * Opens chat in a popup window (450×600px) following the WindowPortal pattern
+ * established in Backing Track/JamTrack players.
+ *
+ * Redux Integration:
+ * - isWindowOpen: Controls visibility
+ * - activeChannel: Determines channel name
+ * - closeChatWindow: Action to close window
+ *
+ * Component hierarchy:
+ * WindowPortal → JKChatHeader + [content area placeholder]
+ *
+ * Note: Message list implementation deferred to Plan 8.2
+ */
+const JKSessionChatWindow = () => {
+  const dispatch = useDispatch();
+
+  // Redux selectors
+  const isWindowOpen = useSelector(selectIsChatWindowOpen);
+  const activeChannel = useSelector(selectActiveChannel);
+
+  // Handlers
+  const handleClose = useCallback(() => {
+    dispatch(closeChatWindow());
+  }, [dispatch]);
+
+  // Channel name formatting
+  const getChannelName = useCallback(() => {
+    if (!activeChannel) return 'Session Chat';
+    if (activeChannel === 'global') return 'Global Chat';
+    // Session-specific channels will be formatted here
+    // For now, default to 'Session Chat'
+    return 'Session Chat';
+  }, [activeChannel]);
+
+  // Conditional render: only show if window is open
+  if (!isWindowOpen) return null;
+
+  return (
+    <WindowPortal
+      title="JamKazam Chat"
+      windowFeatures="width=450,height=600,left=200,top=200,menubar=no,toolbar=no,status=no,scrollbars=no,resizable=yes"
+      onClose={handleClose}
+      windowId="jamkazam-chat"
+    >
+      <div style={{ display: 'flex', flexDirection: 'column', height: '100%' }}>
+        <JKChatHeader
+          channelName={getChannelName()}
+          onClose={handleClose}
+        />
+        <div style={{ flex: 1, padding: '16px', backgroundColor: '#ffffff' }}>
+          {/* Message list placeholder - Plan 8.2 */}
+          <p style={{ color: '#6c757d', textAlign: 'center', marginTop: '24px' }}>
+            Chat messages will appear here
+          </p>
+        </div>
+      </div>
+    </WindowPortal>
+  );
+};
+
+// No PropTypes needed - uses Redux internally
+export default React.memo(JKSessionChatWindow);