diff --git a/apps/web/src/__tests__/polyfill-dialog.ts b/apps/web/src/__tests__/polyfill-dialog.ts
new file mode 100644
index 0000000..a472d56
--- /dev/null
+++ b/apps/web/src/__tests__/polyfill-dialog.ts
@@ -0,0 +1,16 @@
+/**
+ * jsdom doesn't implement HTMLDialogElement.showModal/close.
+ * Call this in beforeAll() for tests that render <Dialog>.
+ */
+export function polyfillDialog(): void {
+	if (typeof HTMLDialogElement.prototype.showModal !== "function") {
+		HTMLDialogElement.prototype.showModal = function showModal() {
+			this.setAttribute("open", "");
+		};
+	}
+	if (typeof HTMLDialogElement.prototype.close !== "function") {
+		HTMLDialogElement.prototype.close = function close() {
+			this.removeAttribute("open");
+		};
+	}
+}
diff --git a/apps/web/src/adapters/bestiary-cache.ts b/apps/web/src/adapters/bestiary-cache.ts
index c8aa7f8..75b27ac 100644
--- a/apps/web/src/adapters/bestiary-cache.ts
+++ b/apps/web/src/adapters/bestiary-cache.ts
@@ -40,7 +40,7 @@ async function getDb(): Promise<IDBPDatabase | null> {
 				}
 				if (oldVersion < 2 && database.objectStoreNames.contains(STORE_NAME)) {
 					// Clear cached creatures to pick up improved tag processing
-					transaction.objectStore(STORE_NAME).clear();
+					void transaction.objectStore(STORE_NAME).clear();
 				}
 			},
 		});
diff --git a/apps/web/src/components/__tests__/action-bar.test.tsx b/apps/web/src/components/__tests__/action-bar.test.tsx
index ae9e1b5..61be700 100644
--- a/apps/web/src/components/__tests__/action-bar.test.tsx
+++ b/apps/web/src/components/__tests__/action-bar.test.tsx
@@ -4,6 +4,7 @@ import "@testing-library/jest-dom/vitest";
 import { cleanup, render, screen } from "@testing-library/react";
 import userEvent from "@testing-library/user-event";
 import { afterEach, beforeAll, describe, expect, it, vi } from "vitest";
+import { polyfillDialog } from "../../__tests__/polyfill-dialog.js";
 import { AllProviders } from "../../__tests__/test-providers.js";
 import { ActionBar } from "../action-bar.js";
 
@@ -50,16 +51,7 @@ beforeAll(() => {
 			dispatchEvent: vi.fn(),
 		})),
 	});
-	HTMLDialogElement.prototype.showModal =
-		HTMLDialogElement.prototype.showModal ||
-		function showModal(this: HTMLDialogElement) {
-			this.setAttribute("open", "");
-		};
-	HTMLDialogElement.prototype.close =
-		HTMLDialogElement.prototype.close ||
-		function close(this: HTMLDialogElement) {
-			this.removeAttribute("open");
-		};
+	polyfillDialog();
 });
 
 afterEach(cleanup);
diff --git a/apps/web/src/components/__tests__/create-player-modal.test.tsx b/apps/web/src/components/__tests__/create-player-modal.test.tsx
index 58ff562..0ac1e29 100644
--- a/apps/web/src/components/__tests__/create-player-modal.test.tsx
+++ b/apps/web/src/components/__tests__/create-player-modal.test.tsx
@@ -4,19 +4,11 @@ import { playerCharacterId } from "@initiative/domain";
 import { cleanup, render, screen } from "@testing-library/react";
 import { userEvent } from "@testing-library/user-event";
 import { afterEach, beforeAll, describe, expect, it, vi } from "vitest";
+import { polyfillDialog } from "../../__tests__/polyfill-dialog.js";
 import { CreatePlayerModal } from "../create-player-modal.js";
 
 beforeAll(() => {
-	HTMLDialogElement.prototype.showModal =
-		HTMLDialogElement.prototype.showModal ||
-		function showModal(this: HTMLDialogElement) {
-			this.setAttribute("open", "");
-		};
-	HTMLDialogElement.prototype.close =
-		HTMLDialogElement.prototype.close ||
-		function close(this: HTMLDialogElement) {
-			this.removeAttribute("open");
-		};
+	polyfillDialog();
 });
 
 afterEach(cleanup);
diff --git a/apps/web/src/components/__tests__/dialog.test.tsx b/apps/web/src/components/__tests__/dialog.test.tsx
index 9c483f4..719f791 100644
--- a/apps/web/src/components/__tests__/dialog.test.tsx
+++ b/apps/web/src/components/__tests__/dialog.test.tsx
@@ -2,19 +2,11 @@
 import { cleanup, render, screen } from "@testing-library/react";
 import { userEvent } from "@testing-library/user-event";
 import { afterEach, beforeAll, describe, expect, it, vi } from "vitest";
+import { polyfillDialog } from "../../__tests__/polyfill-dialog.js";
 import { Dialog, DialogHeader } from "../ui/dialog.js";
 
 beforeAll(() => {
-	HTMLDialogElement.prototype.showModal =
-		HTMLDialogElement.prototype.showModal ||
-		function showModal(this: HTMLDialogElement) {
-			this.setAttribute("open", "");
-		};
-	HTMLDialogElement.prototype.close =
-		HTMLDialogElement.prototype.close ||
-		function close(this: HTMLDialogElement) {
-			this.removeAttribute("open");
-		};
+	polyfillDialog();
 });
 
 afterEach(cleanup);
diff --git a/lefthook.yml b/lefthook.yml
index 8fdaf90..438d7c9 100644
--- a/lefthook.yml
+++ b/lefthook.yml
@@ -24,6 +24,6 @@ pre-commit:
           - name: typecheck
             run: pnpm exec tsc --build
           - name: oxlint
-            run: pnpm oxlint
+            run: pnpm oxlint -- --deny warnings
           - name: test
             run: pnpm test
diff --git a/package.json b/package.json
index 8a3c7e9..cc224fe 100644
--- a/package.json
+++ b/package.json
@@ -31,10 +31,10 @@
 		"knip": "knip",
 		"jscpd": "jscpd",
 		"jsinspect": "jsinspect -c .jsinspectrc apps/web/src packages/domain/src packages/application/src",
-		"oxlint": "oxlint --tsconfig apps/web/tsconfig.json --type-aware",
+		"oxlint": "oxlint --tsconfig apps/web/tsconfig.json --type-aware --deny warnings",
 		"check:ignores": "node scripts/check-lint-ignores.mjs",
 		"check:classnames": "node scripts/check-cn-classnames.mjs",
 		"check:props": "node scripts/check-component-props.mjs",
-		"check": "pnpm audit --audit-level=high && knip && biome check . && node scripts/check-lint-ignores.mjs && node scripts/check-cn-classnames.mjs && node scripts/check-component-props.mjs && jscpd && pnpm jsinspect && tsc --build && oxlint --tsconfig apps/web/tsconfig.json --type-aware && vitest run"
+		"check": "pnpm audit --audit-level=high && knip && biome check . && node scripts/check-lint-ignores.mjs && node scripts/check-cn-classnames.mjs && node scripts/check-component-props.mjs && jscpd && pnpm jsinspect && tsc --build && oxlint --tsconfig apps/web/tsconfig.json --type-aware --deny warnings && vitest run"
 	}
 }