diff --git a/src/strands/strands_api.js b/src/strands/strands_api.js
index 84fa5597a9..fab1714b1c 100644
--- a/src/strands/strands_api.js
+++ b/src/strands/strands_api.js
@@ -103,15 +103,78 @@ function installBuiltinGlobalAccessors(strandsContext) {
 
   for (const name of Object.keys(BUILTIN_GLOBAL_SPECS)) {
     const spec = BUILTIN_GLOBAL_SPECS[name]
-    Object.defineProperty(window, name, {
-      get: () => {
+    const sym = Symbol(`_strands_${name}`)
+
+    // Define on window for global mode only
+    const inst = getRuntimeP5Instance()
+    if (inst?._isGlobal) {
+      Object.defineProperty(window, name, {
+        get: () => {
+          if (strandsContext.active) {
+            return getBuiltinGlobalNode(strandsContext, name);
+          }
+          const inst = getRuntimeP5Instance()
+          return spec.get(inst);
+        },
+        configurable: true,
+      })
+    }
+
+    // Define on p5.prototype for instance mode
+    const originalProtoDesc = Object.getOwnPropertyDescriptor(strandsContext.p5.prototype, name);
+
+    // For data properties (like mouseX), save the initial value into Symbol-keyed store
+    if (originalProtoDesc && 'value' in originalProtoDesc) {
+      strandsContext.p5.prototype[sym] = originalProtoDesc.value;
+    }
+
+    Object.defineProperty(strandsContext.p5.prototype, name, {
+      get: function() {
         if (strandsContext.active) {
           return getBuiltinGlobalNode(strandsContext, name);
         }
-        const inst = getRuntimeP5Instance()
-          return spec.get(inst);
+        // If our setter stored a value on this instance, return it
+        if (Object.prototype.hasOwnProperty.call(this, sym)) {
+          return this[sym];
+        }
+        // Delegate to original getter (e.g. width -> this._renderer?.width)
+        if (originalProtoDesc?.get) {
+          return originalProtoDesc.get.call(this);
+        }
+        // Fall back to Symbol on prototype chain (for data properties like mouseX)
+        return this[sym];
       },
+      set: function(val) {
+        this[sym] = val;
+      },
+      configurable: true,
     })
+
+    // Define on p5.Graphics.prototype for graphics mode
+    const GraphicsProto = strandsContext.p5?.Graphics?.prototype;
+    if (GraphicsProto) {
+      const originalDesc = Object.getOwnPropertyDescriptor(GraphicsProto, name);
+      Object.defineProperty(GraphicsProto, name, {
+        get: function() {
+          if (strandsContext.active) {
+            return getBuiltinGlobalNode(strandsContext, name);
+          }
+          // Delegate to original getter if it exists (class-level getters like width, deltaTime)
+          if (originalDesc?.get) {
+            return originalDesc.get.call(this);
+          }
+          return this[sym];
+        },
+        set: function(val) {
+          if (originalDesc?.set) {
+            originalDesc.set.call(this, val);
+          } else {
+            this[sym] = val;
+          }
+        },
+        configurable: true,
+      })
+    }
   }
   strandsContext._builtinGlobalsAccessorsInstalled = true
 }
diff --git a/test/unit/visual/cases/webgl.js b/test/unit/visual/cases/webgl.js
index 850b0b4a97..5d6b19e609 100644
--- a/test/unit/visual/cases/webgl.js
+++ b/test/unit/visual/cases/webgl.js
@@ -1172,16 +1172,14 @@ visualTest('randomGaussian() in a fragment loop averages to the mean', (p5, scre
 });
 
     visualTest('uses width/height in getFinalColor', (p5, screenshot) => {
-      let firstShader;
-      function firstShaderCallback() {
-        getFinalColor((color) => {
-          color = [width / 60, height / 60, 0, 1];
-          return color;
-        });
-      }
       p5.createCanvas(60, 60, p5.WEBGL);
       p5.pixelDensity(1);
-      firstShader = p5.baseColorShader().modify(firstShaderCallback);
+      const firstShader = p5.baseColorShader().modify(() => {
+        p5.getFinalColor((color) => {
+          color = [p5.width / 60, p5.height / 60, 0, 1];
+          return color;
+        });
+      }, { p5 });
       p5.background(0);
       p5.shader(firstShader);
       p5.noStroke();
diff --git a/test/unit/webgl/p5.Shader.js b/test/unit/webgl/p5.Shader.js
index 499dab8da8..0317cf2d24 100644
--- a/test/unit/webgl/p5.Shader.js
+++ b/test/unit/webgl/p5.Shader.js
@@ -516,8 +516,8 @@ test('returns numbers for builtin globals outside hooks and a strandNode when ca
   myp5.createCanvas(5, 5, myp5.WEBGL);
   myp5.baseMaterialShader().modify(() => {
     myp5.getPixelInputs(inputs => {
-      const mxInHook = window.mouseX;
-      const wInHook = window.width;
+      const mxInHook = myp5.mouseX;
+      const wInHook = myp5.width;
       assert.isTrue(mxInHook.isStrandsNode);
       assert.isTrue(wInHook.isStrandsNode);
       inputs.color = [1, 0, 0, 1];
@@ -525,14 +525,13 @@ test('returns numbers for builtin globals outside hooks and a strandNode when ca
     });
   }, { myp5 });
 
-  const mx = window.mouseX;
-  const w = window.width;
+  const mx = myp5.mouseX;
+  const w = myp5.width;
   assert.isNumber(mx);
   assert.isNumber(w);
   assert.strictEqual(w, myp5.width);
 });
 
-
     test('map() works inside a strands modify callback', () => {
       myp5.createCanvas(50, 50, myp5.WEBGL);
       const testShader = myp5.baseMaterialShader().modify(() => {