feat(playground): add spread param for sigmoid saturation control and fix randomise sync

Add ?spread=0-1 URL param that controls weight initialization scaling,
RL noise scaling per layer, noise cap, and weight decay to prevent
sigmoid output saturation. At spread=0 (original behavior) weights are
uniform [-1,1] and outputs polarise near 0/1. At spread=1 weights use
Xavier scaling (1/sqrt(fan_in)), noise is proportionally reduced, and
10% weight decay per thumbs-down prevents unbounded magnitude drift.

Also fix randomise to re-inject current joystick position and re-run
inference before routing outputs, eliminating the jump on first
joystick move after randomise.

Defaults: tame=1, spread=0.6 across all app variants.

CLAUDE.md

@@ -38,6 +38,27 @@ The `playground/` directory contains a browser-based interactive demo of the NIS
 
 Key files: `js/nisps/` (ML core port), `js/ui/` (visualizer, joystick, controls), `js/synth/` (C15 bridge, param map, arpeggiator), `js/app.js` (wiring).
 
+### URL Parameters
+
+| Param | Range | Default | Effect |
+|-------|-------|---------|--------|
+| `tame` | 0–1 | 1 | Constrains synth output ranges toward safe limits |
+| `spread` | 0–1 | 0.6 | Controls weight initialization, RL noise scaling, and weight decay (see below) |
+
+#### `spread` — sigmoid saturation control
+
+The MLP uses ReLU hidden layers with a sigmoid output layer. With uniform [-1,1] weights, the sum of many weighted inputs at each layer drives sigmoid pre-activations far from zero (std dev ≈ √fan_in), causing outputs to saturate near 0 or 1. The `spread` parameter addresses this:
+
+- **`spread=0`** (polarised): Weights drawn from uniform [-1,1]. RL noise cap = 0.3. Noise applied uniformly across layers. Outputs cluster at extremes — good for exploration of radical mappings.
+- **`spread=1`** (centered): Weights scaled by 1/√fan_in per layer (Xavier initialization). RL noise cap = 0.05. Noise also scaled per-layer. Weight decay prevents magnitude drift. Outputs spread across the full [0,1] range — better for fine-grained RL shaping.
+- **Intermediate values** interpolate linearly between these two regimes.
+
+Affects four code paths:
+1. **`drawWeights(spread)`** — initial randomisation weight scale
+2. **`moveWeights(speed, spread)`** — RL exploration noise scale per layer
+3. **Weight decay in `moveWeights`** — each call decays weights by `10% * spread` before adding noise, preventing unbounded magnitude drift from repeated thumbs-down. At spread=0 there is no decay (original behavior). At spread=1, weights decay ~10% per call, creating a natural equilibrium where exploration noise and decay balance out rather than weights growing until sigmoid permanently saturates.
+4. **Noise cap** in thumbs-down handler — `0.3*(1-spread) + 0.05*spread`
+
 ### C15 Parameter Map
 
 The 126 synth parameters in `js/synth/param-map.js` were curated from the C15's 287 total parameters. Excluded categories:

playground/js/a-app.js

@@ -360,9 +360,9 @@ function padPresetOutputs(outputs) {
 function init() {
   // Parse ?tame URL param
   const urlParams = new URLSearchParams(window.location.search);
-  tameLevel = parseFloat(urlParams.get('tame') ?? '0');
-  spreadLevel = parseFloat(urlParams.get('spread') ?? '0');
-  if (isNaN(spreadLevel)) spreadLevel = 0;
+  tameLevel = parseFloat(urlParams.get('tame') ?? '1');
+  spreadLevel = parseFloat(urlParams.get('spread') ?? '0.6');
+  if (isNaN(spreadLevel)) spreadLevel = 0.6;
   spreadLevel = Math.max(0, Math.min(1, spreadLevel));
 
   // IML — fresh random weights each boot, no state restoration
@@ -754,11 +754,18 @@ function wireControls() {
     });
   });
 
-  // Output mode toggle
+  // Output mode toggle (sheet)
   document.querySelectorAll('#output-toggle .pill-opt').forEach(btn => {
     btn.addEventListener('click', () => {
-      document.querySelectorAll('#output-toggle .pill-opt').forEach(b => b.classList.remove('active'));
-      btn.classList.add('active');
+      syncOutputToggles(btn.dataset.mode);
+      setOutputMode(btn.dataset.mode);
+    });
+  });
+
+  // Output mode toggle (floating)
+  document.querySelectorAll('#output-toggle-float .otf-opt').forEach(btn => {
+    btn.addEventListener('click', () => {
+      syncOutputToggles(btn.dataset.mode);
       setOutputMode(btn.dataset.mode);
     });
   });
@@ -800,6 +807,11 @@ function updateModeUI() {
   }
 }
 
+function syncOutputToggles(mode) {
+  document.querySelectorAll('#output-toggle .pill-opt').forEach(b => b.classList.toggle('active', b.dataset.mode === mode));
+  document.querySelectorAll('#output-toggle-float .otf-opt').forEach(b => b.classList.toggle('active', b.dataset.mode === mode));
+}
+
 function setOutputMode(mode) {
   outputMode = mode;
   buildHeatmap();
@@ -869,6 +881,9 @@ function onTrain() {
 
 function onRandomize() {
   iml.randomiseWeights(spreadLevel);
+  iml.setInput(0, joyX);
+  iml.setInput(1, joyY);
+  iml.process();
   const outputs = iml.getOutputs();
   routeOutputs(outputs);
   updateHeatmap(outputs);
@@ -908,9 +923,10 @@ function onThumbsUp() {
 }
 
 function onThumbsDown() {
-  noiseLevel = Math.min(noiseLevel * 1.5, 0.3);
+  const noiseCap = 0.3 * (1 - spreadLevel) + 0.05 * spreadLevel;
+  noiseLevel = Math.min(noiseLevel * 1.5, noiseCap);
 
-  iml.moveWeights(noiseLevel);
+  iml.moveWeights(noiseLevel, spreadLevel);
 
   const outputs = iml.getOutputs();
   routeOutputs(outputs);
@@ -1340,9 +1356,7 @@ function loadState() {
     // Restore output mode
     if (state.outputMode && state.outputMode !== outputMode) {
       setOutputMode(state.outputMode);
-      document.querySelectorAll('#output-toggle .pill-opt').forEach(b => {
-        b.classList.toggle('active', b.dataset.mode === outputMode);
-      });
+      syncOutputToggles(outputMode);
     }
 
     console.log(`[NISPS] Restored ${state.features?.length || 0} examples from storage`);

playground/js/app.js

@@ -46,10 +46,10 @@ let arpeggiator = null;
 // Devmode: tame level (0 = no mitigation, 1 = strongest)
 // Set via URL ?tame=0.7 or window.setTameLevel(0.7)
 const _urlParams = new URLSearchParams(location.search);
-let tameLevel = parseFloat(_urlParams.get('tame') ?? '0.7');
-if (isNaN(tameLevel)) tameLevel = 0.7;
+let tameLevel = parseFloat(_urlParams.get('tame') ?? '1');
+if (isNaN(tameLevel)) tameLevel = 1;
 tameLevel = Math.max(0, Math.min(1, tameLevel));
-let spreadLevel = parseFloat(_urlParams.get('spread') ?? '0');
+let spreadLevel = parseFloat(_urlParams.get('spread') ?? '0.6');
 if (isNaN(spreadLevel)) spreadLevel = 0.6;
 spreadLevel = Math.max(0, Math.min(1, spreadLevel));
 window.setTameLevel = (v) => { tameLevel = Math.max(0, Math.min(1, v)); console.log(`[NISPS] tame=${tameLevel}`); };
@@ -345,6 +345,9 @@ function onTrain() {
 
 function onRandomize() {
   iml.randomiseWeights(spreadLevel);
+  iml.setInput(0, joystick.x);
+  iml.setInput(1, joystick.y);
+  iml.process();
   const outputs = iml.getOutputs();
   routeOutputs(outputs);
   paramDisplay.update(outputs);
@@ -387,10 +390,12 @@ function onThumbsUp() {
 
 function onThumbsDown() {
   // Increase noise for more exploration
-  noiseLevel = Math.min(noiseLevel * 1.5, 0.3);
+  // spread reduces the noise cap: at spread=1 cap is 0.05 (vs 0.3 at spread=0)
+  const noiseCap = 0.3 * (1 - spreadLevel) + 0.05 * spreadLevel;
+  noiseLevel = Math.min(noiseLevel * 1.5, noiseCap);
 
-  // Perturb weights
-  iml.moveWeights(noiseLevel);
+  // Perturb weights (spread scales noise per-layer by 1/sqrt(fan_in))
+  iml.moveWeights(noiseLevel, spreadLevel);
 
   const outputs = iml.getOutputs();
   routeOutputs(outputs);

playground/js/b-app.js

@@ -90,8 +90,8 @@ function heatmapColor(t) {
 
 // --- Tame URL param ---
 const _urlParams = new URLSearchParams(window.location.search);
-const tameLevel = parseFloat(_urlParams.get('tame') ?? '0');
-const spreadLevel = Math.max(0, Math.min(1, parseFloat(_urlParams.get('spread') ?? '0') || 0));
+const tameLevel = parseFloat(_urlParams.get('tame') ?? '1');
+const spreadLevel = Math.max(0, Math.min(1, parseFloat(_urlParams.get('spread') ?? '0.6') || 0.6));
 
 // --- State ---
 let iml;
@@ -736,6 +736,9 @@ function onTrain() {
 
 function onRandomize() {
   iml.randomiseWeights(spreadLevel);
+  iml.setInput(0, joyX);
+  iml.setInput(1, joyY);
+  iml.process();
   const outputs = iml.getOutputs();
   routeOutputs(outputs);
   updateAllParamBars(outputs);
@@ -772,8 +775,9 @@ function onThumbsUp() {
 }
 
 function onThumbsDown() {
-  noiseLevel = Math.min(noiseLevel * 1.5, 0.3);
-  iml.moveWeights(noiseLevel);
+  const noiseCap = 0.3 * (1 - spreadLevel) + 0.05 * spreadLevel;
+  noiseLevel = Math.min(noiseLevel * 1.5, noiseCap);
+  iml.moveWeights(noiseLevel, spreadLevel);
   const outputs = iml.getOutputs();
   routeOutputs(outputs);
   updateAllParamBars(outputs);

playground/js/c-app.js

@@ -48,8 +48,8 @@ const PRESETS = [
 
 // --- Tame URL param ---
 const _urlParams = new URLSearchParams(window.location.search);
-const tameLevel = parseFloat(_urlParams.get('tame') ?? '0');
-const spreadLevel = Math.max(0, Math.min(1, parseFloat(_urlParams.get('spread') ?? '0') || 0));
+const tameLevel = parseFloat(_urlParams.get('tame') ?? '1');
+const spreadLevel = Math.max(0, Math.min(1, parseFloat(_urlParams.get('spread') ?? '0.6') || 0.6));
 
 // ============================================================
 // State
@@ -630,6 +630,10 @@ function wireTeachActions() {
   document.getElementById('btn-clear')?.addEventListener('click', () => {
     iml.clearDataset();
     iml.randomiseWeights(spreadLevel);
+    iml.setInput(0, joystickX);
+    iml.setInput(1, joystickY);
+    iml.process();
+    routeOutputs(iml.getOutputs());
     selectedPreset = -1;
     document.querySelectorAll('.preset-thumb').forEach(b => b.classList.remove('selected'));
     updateTeachStatus();
@@ -688,8 +692,9 @@ function onThumbsUp() {
 }
 
 function onThumbsDown() {
-  noiseLevel = Math.min(0.3, noiseLevel * 1.5);
-  iml.moveWeights(noiseLevel);
+  const noiseCap = 0.3 * (1 - spreadLevel) + 0.05 * spreadLevel;
+  noiseLevel = Math.min(noiseCap, noiseLevel * 1.5);
+  iml.moveWeights(noiseLevel, spreadLevel);
   iml.setInput(0, joystickX);
   iml.setInput(1, joystickY);
   iml.process();

playground/js/nisps/iml.js

@@ -158,8 +158,9 @@ export class IML {
   }
 
   // Add Gaussian noise to weights (for RL exploration)
-  moveWeights(speed) {
-    this.mlp.moveWeights(speed);
+  // spread: 0 = flat noise, 1 = Xavier-scaled per layer
+  moveWeights(speed, spread = 0) {
+    this.mlp.moveWeights(speed, spread);
     // Run inference to show effect
     this.inputUpdated = true;
     this.process();

playground/js/nisps/mlp.js

@@ -221,16 +221,29 @@ export class MLP {
   }
 
   // MoveWeights - add Gaussian noise (port of gen_randn)
-  moveWeights(speed) {
-    for (const layer of this.layers) {
-      for (const node of layer.nodes) {
+  // spread: 0 = flat noise across all layers (original), 1 = scale noise by 1/sqrt(fan_in)
+  // per layer so perturbations stay proportional to Xavier-scale weights and don't
+  // saturate sigmoid outputs.
+  // Weight decay (proportional to spread) shrinks weights toward zero before adding noise,
+  // preventing unbounded magnitude drift from repeated thumbs-down. At spread=0 there is
+  // no decay (original behavior). At spread=1 each call decays weights by ~10%, creating
+  // a natural equilibrium where exploration can't permanently saturate sigmoid.
+  moveWeights(speed, spread = 0) {
+    const decay = 1 - 0.1 * spread; // spread=0 → 1.0 (no decay), spread=1 → 0.9
+    for (let l = 0; l < this.layers.length; l++) {
+      const fanIn = this.layersNodes[l];
+      const xavierScale = 1 / Math.sqrt(fanIn);
+      const layerScale = 1 * (1 - spread) + xavierScale * spread;
+      for (const node of this.layers[l].nodes) {
         for (let j = 0; j < node.weights.length; j++) {
+          // Decay toward zero to prevent magnitude drift
+          node.weights[j] *= decay;
           // gen_randn: sum of 3 uniform randoms * kN_times * stddev + mean
           let accum = 0;
           for (let n = 0; n < 3; n++) {
             accum += Math.random() * 2 - 1; // gen_rand with range 2.0
           }
-          node.weights[j] = 3 * accum * speed + node.weights[j];
+          node.weights[j] += 3 * accum * speed * layerScale;
         }
       }
     }