knn scatter: revert to real-data only (no demo handlers)

The KNN producer works; KNN does not need a demo-mode fallback.
Remove demo_start / demo_stop / cachedReal / demoActive scaffolding
that I'd added speculatively. Embedding events render directly.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

training/dashboard/static/dashboard.js

@@ -2102,29 +2102,8 @@ def train_nn(*, model, X_train, y_train, X_val, y_val,
       rebuildLegend();
     }
 
-    // Exclusive: demo on → only synthetic clusters; demo off → only
-    // real embedding events. cachedReal accumulates real points
-    // even while demo is on, so demo_stop restores them.
-    let demoActive = false;
-    const cachedReal = [];
-    const REAL_CACHE_CAP = 5000;
-    function repaintFromReal() {
-      points.length = 0;
-      resetStats();
-      for (const pt of cachedReal) {
-        points.push(pt);
-        addStat(pt);
-      }
-      rebuildLegend();
-    }
-    on('demo_start', () => {
-      demoActive = true;
-      loadSynthetic();
-    });
-    on('demo_stop', () => {
-      demoActive = false;
-      repaintFromReal();
-    });
+    // KNN scatter is real-data only: it has a working producer and
+    // doesn't participate in demo mode at all.
     on('embedding', m => {
       if (typeof m.x !== 'number' || typeof m.y !== 'number') return;
       const pt = {
@@ -2134,13 +2113,9 @@ def train_nn(*, model, X_train, y_train, X_val, y_val,
         predicted: m.predicted,
         cluster: typeof m.cluster === 'number' ? m.cluster : undefined,
       };
-      cachedReal.push(pt);
-      if (cachedReal.length > REAL_CACHE_CAP) cachedReal.shift();
-      if (!demoActive) {
-        points.push(pt);
-        addStat(pt);
-        rebuildLegend();
-      }
+      points.push(pt);
+      addStat(pt);
+      rebuildLegend();
     });
 
     rebuildLegend();

training/dashboard/static/index.html

@@ -1314,6 +1314,6 @@
     </article>
   </div>
 
-  <script src="/static/dashboard.js?v=33d3c0e6"></script>
+  <script src="/static/dashboard.js?v=2a8b8c03"></script>
 </body>
 </html>