demo mode: backfill phase mix + knn metric (no clobber on real data)

Two targeted fixes for the demo-toggle path; intentionally narrow so
we don't override widgets that already work in both modes (KNN
scatter, DB explorer).

Phase-mix bar
- Tracks `hasRealMix` and only injects a synthetic fallback on
  demo_start if no real snapshot/phase_mix event has been seen.
  If real data later arrives, applyMix overwrites the synthetic
  value automatically.
- Synthetic numbers mirror a real production run (500/78705
  episodes, ~4.5 hours of weighted seconds) so the bar reads
  correctly during a deck-only demo.

KNN model_metric
- Periodic demoTick tweaks now include `knn` alongside rnn/gru/lstm/
  bert. Initial demo_start already populated all five bars; the
  periodic tweak just keeps the knn bar from sitting frozen.

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

training/dashboard/static/dashboard.js

@@ -238,8 +238,8 @@
     }
     // Occasionally tweak a model metric so the bars aren't static.
     if (Math.random() < 0.05) {
-      const m = ['rnn', 'gru', 'lstm', 'bert'][Math.floor(Math.random() * 4)];
-      const base = { rnn: 0.872, gru: 0.911, lstm: 0.928, bert: 0.954 }[m];
+      const m = ['knn', 'rnn', 'gru', 'lstm', 'bert'][Math.floor(Math.random() * 5)];
+      const base = { knn: 0.736, rnn: 0.872, gru: 0.911, lstm: 0.928, bert: 0.954 }[m];
       dispatch({ type: 'model_metric', model: m, accuracy: base + (Math.random() - 0.5) * 0.012 });
     }
   }
@@ -1345,8 +1345,15 @@ def train_nn(*, model, X_train, y_train, X_val, y_val,
 
     function fmtInt(n) { return (typeof n === 'number') ? n.toLocaleString() : '—'; }
 
+    // Tracks whether real phase_mix data has arrived. demo_start uses
+    // this to decide whether to inject a synthetic fallback — if real
+    // data is already present (from snapshot or the phase_mix feeder),
+    // the demo toggle does NOT clobber it.
+    let hasRealMix = false;
+
     function applyMix(mix) {
       if (!mix) return;
+      hasRealMix = true;
       const w = mix.weighted_seconds || {};
       const c = mix.counts || {};
       // Prefer time-weighted proportions; fall back to label counts.
@@ -1378,6 +1385,31 @@ def train_nn(*, model, X_train, y_train, X_val, y_val,
 
     on('snapshot', m => { if (m.phase_mix) applyMix(m.phase_mix); });
     on('phase_mix', applyMix);
+    on('demo_start', () => {
+      // Synthetic fallback: only fires if no real phase_mix has
+      // arrived yet (e.g. dashboard offline, or feeder hasn't done its
+      // first compute). The numbers below mirror a real production run
+      // so the bar reads correctly during a deck-only demo. If real
+      // data later arrives via snapshot or phase_mix event, applyMix
+      // overwrites this on the spot.
+      if (hasRealMix) return;
+      applyMix({
+        weighted_seconds: {
+          clean: 2659.1, armed: 725.7, infecting: 1607.4,
+          infected_running: 8308.3, dormant: 3059.3,
+        },
+        counts: {
+          clean: 451, armed: 198, infecting: 379,
+          infected_running: 614, dormant: 223,
+        },
+        sampled_episodes: 500,
+        population_episodes: 78705,
+        total_labels: 1865,
+      });
+      // applyMix flipped hasRealMix to true — flip back so a future
+      // real arrival is still recognised as the first real one.
+      hasRealMix = false;
+    });
     on('demo_stop', () => {
       // Demo toggle off doesn't wipe the dataset mix — the dataset is
       // ground truth, the demo only fakes per-event widgets.

training/dashboard/static/index.html

@@ -1314,6 +1314,6 @@
     </article>
   </div>
 
-  <script src="/static/dashboard.js?v=7c6859eb"></script>
+  <script src="/static/dashboard.js?v=883a2c24"></script>
 </body>
 </html>