diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3ac46ad..db47ce9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,9 @@
+## Unreleased
+
+### Bug Fixes
+
+- **logic-engine:** prevent trigger sandbox evaluation from freezing host prototypes while preserving `return`-based logic scripts; reported in [#496](https://github.com/the-open-engine/zeroshot/pull/496).
+
 # [5.3.0](https://github.com/covibes/zeroshot/compare/v5.2.1...v5.3.0) (2026-01-12)
 
 ### Bug Fixes
diff --git a/src/logic-engine.js b/src/logic-engine.js
index b9a108b..d1e639d 100644
--- a/src/logic-engine.js
+++ b/src/logic-engine.js
@@ -82,10 +82,6 @@ function buildAgentContext(agent) {
   };
 }
 
-function getSafeBuiltins() {
-  return { Set, Map, Array, Object, String, Number, Boolean, Math, Date, JSON };
-}
-
 function getQuietConsole() {
   return {
     log: () => {},
@@ -114,33 +110,19 @@ class LogicEngine {
       // Build sandbox context
       const context = this._buildContext(agent, message);
 
-      // Create isolated context with frozen prototypes
-      // This prevents prototype pollution attacks
-      const isolatedContext = {};
-
-      // Freeze Object, Array, Function prototypes in the sandbox
-      isolatedContext.Object = Object.freeze({ ...Object });
-      isolatedContext.Array = Array;
-      isolatedContext.Function = Function;
+      // Contextify before execution so scripts use VM-owned globals instead of
+      // host constructors. Keep the function-body contract: trigger scripts use
+      // return statements throughout built-in templates and user configs.
+      const sandbox = { ...context };
+      vm.createContext(sandbox);
 
-      // Copy safe context properties
-      Object.assign(isolatedContext, context);
-
-      // Wrap script to prevent prototype access
       const wrappedScript = `(function() {
         'use strict';
-        // Prevent prototype pollution
-        const frozenObject = Object;
-        const frozenArray = Array;
-        Object.freeze(frozenObject.prototype);
-        Object.freeze(frozenArray.prototype);
-
         ${script}
       })()`;
 
-      // Create and run in context
-      vm.createContext(isolatedContext);
-      const result = vm.runInContext(wrappedScript, isolatedContext, {
+      // Run in context
+      const result = vm.runInContext(wrappedScript, sandbox, {
         timeout: this.timeout,
         displayErrors: true,
       });
@@ -168,7 +150,6 @@ class LogicEngine {
       ledger: ledgerAPI,
       cluster: buildClusterAPI(this.cluster, clusterId),
       helpers: buildHelpers(ledgerAPI),
-      ...getSafeBuiltins(),
       console: getQuietConsole(),
     };
   }
diff --git a/tests/integration/trigger-evaluation.test.js b/tests/integration/trigger-evaluation.test.js
index 36ecd22..6543e2e 100644
--- a/tests/integration/trigger-evaluation.test.js
+++ b/tests/integration/trigger-evaluation.test.js
@@ -6,6 +6,7 @@
  */
 
 const assert = require('node:assert');
+const { spawnSync } = require('child_process');
 const path = require('path');
 const fs = require('fs');
 const os = require('os');
@@ -417,6 +418,42 @@ function defineScriptValidationTests() {
       assert.strictEqual(validResult.valid, true);
       assert.strictEqual(invalidResult.valid, false);
     });
+
+    it('should not freeze host prototypes when evaluating scripts', () => {
+      const childScript = `
+        const LogicEngine = require(${JSON.stringify(path.resolve(__dirname, '../../src/logic-engine'))});
+        const messageBus = {
+          query: () => [],
+          findLast: () => null,
+          count: () => 0,
+          since: () => [],
+        };
+        const engine = new LogicEngine(messageBus, { id: 'test-cluster', agents: [] });
+        const result = engine.evaluate(
+          'return true;',
+          { id: 'evaluator', cluster_id: 'test-cluster' },
+          { topic: 'TRIGGER' }
+        );
+        console.log(JSON.stringify({
+          result,
+          objectPrototypeFrozen: Object.isFrozen(Object.prototype),
+          arrayPrototypeFrozen: Object.isFrozen(Array.prototype),
+        }));
+      `;
+
+      const child = spawnSync(process.execPath, ['-e', childScript], {
+        encoding: 'utf8',
+      });
+
+      assert.strictEqual(child.status, 0, child.stderr || child.stdout);
+      const output = JSON.parse(child.stdout.trim());
+
+      assert.deepStrictEqual(output, {
+        result: true,
+        objectPrototypeFrozen: false,
+        arrayPrototypeFrozen: false,
+      });
+    });
   });
 }