diff --git a/test/harness/package-lock.json b/test/harness/package-lock.json
index 9ed1974e95..9ee31ade82 100644
--- a/test/harness/package-lock.json
+++ b/test/harness/package-lock.json
@@ -9,7 +9,7 @@
       "version": "1.0.0",
       "license": "ISC",
       "devDependencies": {
-        "@github/copilot": "^0.0.400",
+        "@github/copilot": "^0.0.421",
         "@types/node": "^25.2.0",
         "openai": "^6.17.0",
         "tsx": "^4.21.0",
@@ -461,27 +461,27 @@
       }
     },
     "node_modules/@github/copilot": {
-      "version": "0.0.400",
-      "resolved": "https://registry.npmjs.org/@github/copilot/-/copilot-0.0.400.tgz",
-      "integrity": "sha512-OliuUpFFtgp2WN/LEpj9Gzmbe4SyRLWsbqcYnJojAN1whd0l8JgnJBqzo3LXkZf5nUbVQ57IlU93BpjbIhmHrQ==",
+      "version": "0.0.421",
+      "resolved": "https://registry.npmjs.org/@github/copilot/-/copilot-0.0.421.tgz",
+      "integrity": "sha512-nDUt9f5al7IgBOTc7AwLpqvaX61VsRDYDQ9D5iR0QQzHo4pgDcyOXIjXUQUKsJwObXHfh6qR+Jm1vnlbw5cacg==",
       "dev": true,
       "license": "SEE LICENSE IN LICENSE.md",
       "bin": {
         "copilot": "npm-loader.js"
       },
       "optionalDependencies": {
-        "@github/copilot-darwin-arm64": "0.0.400",
-        "@github/copilot-darwin-x64": "0.0.400",
-        "@github/copilot-linux-arm64": "0.0.400",
-        "@github/copilot-linux-x64": "0.0.400",
-        "@github/copilot-win32-arm64": "0.0.400",
-        "@github/copilot-win32-x64": "0.0.400"
+        "@github/copilot-darwin-arm64": "0.0.421",
+        "@github/copilot-darwin-x64": "0.0.421",
+        "@github/copilot-linux-arm64": "0.0.421",
+        "@github/copilot-linux-x64": "0.0.421",
+        "@github/copilot-win32-arm64": "0.0.421",
+        "@github/copilot-win32-x64": "0.0.421"
       }
     },
     "node_modules/@github/copilot-darwin-arm64": {
-      "version": "0.0.400",
-      "resolved": "https://registry.npmjs.org/@github/copilot-darwin-arm64/-/copilot-darwin-arm64-0.0.400.tgz",
-      "integrity": "sha512-Grpv/lYiLih0W8G/ofueNApz3WRGPkCFDM7i1ecc0slfI/JkjyQIjZWnD7a4lK5iSjBWQGIaKTHSj8e//d8Gug==",
+      "version": "0.0.421",
+      "resolved": "https://registry.npmjs.org/@github/copilot-darwin-arm64/-/copilot-darwin-arm64-0.0.421.tgz",
+      "integrity": "sha512-S4plFsxH7W8X1gEkGNcfyKykIji4mNv8BP/GpPs2Ad84qWoJpZzfZsjrjF0BQ8mvFObWp6Ft2SZOnJzFZW1Ftw==",
       "cpu": [
         "arm64"
       ],
@@ -496,9 +496,9 @@
       }
     },
     "node_modules/@github/copilot-darwin-x64": {
-      "version": "0.0.400",
-      "resolved": "https://registry.npmjs.org/@github/copilot-darwin-x64/-/copilot-darwin-x64-0.0.400.tgz",
-      "integrity": "sha512-c/qJC6qJIXjr5D274EvZc1FyKAktWrz2n6zjyHoqix8o8VJEfSo+Sqk4DPV1eZrrYCyE1EQyfNLvv80x1+pcTQ==",
+      "version": "0.0.421",
+      "resolved": "https://registry.npmjs.org/@github/copilot-darwin-x64/-/copilot-darwin-x64-0.0.421.tgz",
+      "integrity": "sha512-h+Dbfq8ByAielLYIeJbjkN/9Abs6AKHFi+XuuzEy4YA9jOA42uKMFsWYwaoYH8ZLK9Y+4wagYI9UewVPnyIWPA==",
       "cpu": [
         "x64"
       ],
@@ -513,9 +513,9 @@
       }
     },
     "node_modules/@github/copilot-linux-arm64": {
-      "version": "0.0.400",
-      "resolved": "https://registry.npmjs.org/@github/copilot-linux-arm64/-/copilot-linux-arm64-0.0.400.tgz",
-      "integrity": "sha512-8pcKXjFopVHZmAK4nFfV48/KN3WwmVm4HDcpPESvNHjoRj8PuFN9Ef9llD6QKerYbQc38C+Pu21IXimRvqqKHg==",
+      "version": "0.0.421",
+      "resolved": "https://registry.npmjs.org/@github/copilot-linux-arm64/-/copilot-linux-arm64-0.0.421.tgz",
+      "integrity": "sha512-cxlqDRR/wKfbdzd456N2h7sZOZY069wU2ycSYSmo7cC75U5DyhMGYAZwyAhvQ7UKmS5gJC/wgSgye0njuK22Xg==",
       "cpu": [
         "arm64"
       ],
@@ -530,9 +530,9 @@
       }
     },
     "node_modules/@github/copilot-linux-x64": {
-      "version": "0.0.400",
-      "resolved": "https://registry.npmjs.org/@github/copilot-linux-x64/-/copilot-linux-x64-0.0.400.tgz",
-      "integrity": "sha512-BW+u6m/z894KHwJWNWGDiFAfMv83U1B1DVxrzJ1vdmGn05R9jIOp0TNaZtv0jh/ycGiQJ8s2cxFdcKtWxEcenQ==",
+      "version": "0.0.421",
+      "resolved": "https://registry.npmjs.org/@github/copilot-linux-x64/-/copilot-linux-x64-0.0.421.tgz",
+      "integrity": "sha512-7np5b6EEemJ3U3jnl92buJ88nlpqOAIrLaJxx3pJGrP9SVFMBD/6EAlfIQ5m5QTfs+/vIuTKWBrq1wpFVZZUcQ==",
       "cpu": [
         "x64"
       ],
@@ -547,9 +547,9 @@
       }
     },
     "node_modules/@github/copilot-win32-arm64": {
-      "version": "0.0.400",
-      "resolved": "https://registry.npmjs.org/@github/copilot-win32-arm64/-/copilot-win32-arm64-0.0.400.tgz",
-      "integrity": "sha512-p299J676Q8BepAcR1DPMBqvW9M2nMr+fHfNyD5ketEHHc2gDF2KaWW83iXD0HqF5df7La7gbgJXYonL9Ct11Sw==",
+      "version": "0.0.421",
+      "resolved": "https://registry.npmjs.org/@github/copilot-win32-arm64/-/copilot-win32-arm64-0.0.421.tgz",
+      "integrity": "sha512-T6qCqOnijD5pmC0ytVsahX3bpDnXtLTgo9xFGo/BGaPEvX02ePkzcRZkfkOclkzc8QlkVji6KqZYB+qMZTliwg==",
       "cpu": [
         "arm64"
       ],
@@ -564,9 +564,9 @@
       }
     },
     "node_modules/@github/copilot-win32-x64": {
-      "version": "0.0.400",
-      "resolved": "https://registry.npmjs.org/@github/copilot-win32-x64/-/copilot-win32-x64-0.0.400.tgz",
-      "integrity": "sha512-y/77mfEB7MP2eHaRasYBKTnbO/BzaRp6jeSkPC+WUZqR62kRxmvBYCbVmBK66PZ1W6UFbwNPdHBQHebfuOePvg==",
+      "version": "0.0.421",
+      "resolved": "https://registry.npmjs.org/@github/copilot-win32-x64/-/copilot-win32-x64-0.0.421.tgz",
+      "integrity": "sha512-KDfy3wsRQFIcOQDdd5Mblvh+DWRq+UGbTQ34wyW36ws1BsdWkV++gk9bTkeJRsPbQ51wsJ0V/jRKEZv4uK5dTA==",
       "cpu": [
         "x64"
       ],
diff --git a/test/harness/package.json b/test/harness/package.json
index 76b4ccb4aa..bfc50fa4ff 100644
--- a/test/harness/package.json
+++ b/test/harness/package.json
@@ -11,7 +11,7 @@
     "test": "vitest run"
   },
   "devDependencies": {
-    "@github/copilot": "^0.0.400",
+    "@github/copilot": "^0.0.421",
     "@types/node": "^25.2.0",
     "openai": "^6.17.0",
     "tsx": "^4.21.0",