diff --git a/biome.json b/biome.json
index 92cd200..52c4f60 100644
--- a/biome.json
+++ b/biome.json
@@ -183,6 +183,16 @@
           }
         }
       }
+    },
+    {
+      "includes": ["tests/**"],
+      "linter": {
+        "rules": {
+          "nursery": {
+            "useExplicitType": "off"
+          }
+        }
+      }
     }
   ],
   "javascript": {
diff --git a/package-lock.json b/package-lock.json
index 269fa57..f1edadb 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -4681,9 +4681,9 @@
       }
     },
     "node_modules/brace-expansion": {
-      "version": "5.0.6",
-      "resolved": "https://registry.npmjs.org/brace-expansion/-/brace-expansion-5.0.6.tgz",
-      "integrity": "sha512-kLpxurY4Z4r9sgMsyG0Z9uzsBlgiU/EFKhj/h91/8yHu0edo7XuixOIH3VcJ8kkxs6/jPzoI6U9Vj3WqbMQ94g==",
+      "version": "5.0.7",
+      "resolved": "https://registry.npmjs.org/brace-expansion/-/brace-expansion-5.0.7.tgz",
+      "integrity": "sha512-7oFy703dxfY3/NLxC1fh2SUCQ0H9rmAY+5EpDVfXjUTTs+HEwR2nYaqLv+GWcTsumwxPfiz6CzCNkwXwBUwqCA==",
       "dev": true,
       "license": "MIT",
       "dependencies": {
@@ -5403,9 +5403,9 @@
       "license": "MIT"
     },
     "node_modules/fast-uri": {
-      "version": "3.1.2",
-      "resolved": "https://registry.npmjs.org/fast-uri/-/fast-uri-3.1.2.tgz",
-      "integrity": "sha512-rVjf7ArG3LTk+FS6Yw81V1DLuZl1bRbNrev6Tmd/9RaroeeRRJhAt7jg/6YFxbvAQXUCavSoZhPPj6oOx+5KjQ==",
+      "version": "3.1.4",
+      "resolved": "https://registry.npmjs.org/fast-uri/-/fast-uri-3.1.4.tgz",
+      "integrity": "sha512-8JnbkQ4juDyvYs4mgFGQqg4yCYtFDtUtmp2QIQq11ZZe5CFQ5wcqm1rqDgAh/QdMySuBnPzMUiJUNZG5N/AiQw==",
       "dev": true,
       "funding": [
         {
@@ -5461,9 +5461,9 @@
       "license": "MIT"
     },
     "node_modules/filelist/node_modules/brace-expansion": {
-      "version": "2.1.1",
-      "resolved": "https://registry.npmjs.org/brace-expansion/-/brace-expansion-2.1.1.tgz",
-      "integrity": "sha512-WR1cURNjuvBLMZBMbqM0UoE+WAfdUcEV1ccD8PVBVOI+Z3ND4+SZbN8RsfT2bMuG1qwz5RFvPukSZm5fF2D5eA==",
+      "version": "2.1.2",
+      "resolved": "https://registry.npmjs.org/brace-expansion/-/brace-expansion-2.1.2.tgz",
+      "integrity": "sha512-w5JZcKgdhDOgOwm8H+KgbosopHMuGcl6qbulwjtz3SM7I7P3yW1eAjzMPLrIE+NQ9vjgANKHWeMHnrT0OXW1oA==",
       "dev": true,
       "license": "MIT",
       "dependencies": {
diff --git a/playwright.config.ts b/playwright.config.ts
index dffd571..66c95b7 100644
--- a/playwright.config.ts
+++ b/playwright.config.ts
@@ -11,7 +11,7 @@ export default defineConfig({
     timeout: 10_000,
   },
   fullyParallel: false,
-  forbidOnly: !!process.env.CI,
+  forbidOnly: !!process.env["CI"],
   retries: 0,
   workers: 1,
   reporter: [["list"], ["html", { open: "never" }]],
@@ -24,7 +24,7 @@ export default defineConfig({
   webServer: {
     command: "npm run start",
     url: "http://localhost:5173",
-    reuseExistingServer: !process.env.CI,
+    reuseExistingServer: !process.env["CI"],
     timeout: 120_000,
   },
   projects: [
diff --git a/src/common/TimeModel.ts b/src/common/TimeModel.ts
index a29ce9f..e8671c2 100644
--- a/src/common/TimeModel.ts
+++ b/src/common/TimeModel.ts
@@ -31,7 +31,6 @@
  *   import { TimeControlNode } from "scenerystack/scenery-phet";
  *
  *   const timeControl = new TimeControlNode( model.timer.isPlayingProperty, {
- *     timeSpeedProperty: model.timer.timeSpeedProperty, // optional
  *     playPauseStepButtonOptions: {
  *       stepForwardButtonOptions: {
  *         listener: () => model.step( 1 / 60 ),
diff --git a/src/i18n/StringManager.ts b/src/i18n/StringManager.ts
index 627d9e4..fc9412c 100644
--- a/src/i18n/StringManager.ts
+++ b/src/i18n/StringManager.ts
@@ -26,11 +26,17 @@ import stringsEs from "./strings_es.json";
 import stringsFr from "./strings_fr.json";
 
 // ── Compile-time key-parity check ─────────────────────────────────────────────
-// TypeScript errors here if any locale file is missing a key from English.
+// English is the canonical shape; every other locale must match it exactly.
+// TypeScript errors here if any locale file is missing (or adds) a key relative to
+// English. Add one `satisfies` line per new locale so the check stays exhaustive.
+// biome-ignore lint/complexity/noVoid: intentional compile-time type assertion
+void (stringsFr satisfies typeof stringsEn);
 // biome-ignore lint/complexity/noVoid: intentional compile-time type assertion
 void (stringsEn satisfies typeof stringsFr);
 // biome-ignore lint/complexity/noVoid: intentional compile-time type assertion
-void (stringsFr satisfies typeof stringsEn);
+void (stringsEs satisfies typeof stringsEn);
+// biome-ignore lint/complexity/noVoid: intentional compile-time type assertion
+void (stringsEn satisfies typeof stringsEs);
 
 // ── Build the reactive string property tree ───────────────────────────────────
 const stringProperties = LocalizedString.getNestedStringProperties({
diff --git a/src/main.ts b/src/main.ts
index f3858ca..540572a 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -74,6 +74,3 @@ onReadyToLaunch(() => {
 
   sim.start();
 });
-// hook test
-// test
-// test
diff --git a/tsconfig.scripts.json b/tsconfig.scripts.json
index 526c16e..6e0601b 100644
--- a/tsconfig.scripts.json
+++ b/tsconfig.scripts.json
@@ -4,5 +4,5 @@
     "noEmit": true,
     "types": ["node"]
   },
-  "include": ["scripts"]
+  "include": ["scripts", "*.config.ts"]
 }