diff --git a/frontend/tests/e2e/admin-disable-customer.spec.ts b/frontend/tests/e2e/admin-disable-customer.spec.ts
index 937c47e..f7f93cb 100644
--- a/frontend/tests/e2e/admin-disable-customer.spec.ts
+++ b/frontend/tests/e2e/admin-disable-customer.spec.ts
@@ -33,10 +33,12 @@ test.describe('Disabling a customer account', () => {
     await accountModal.open();
     await expect(accountModal.emailText(customer.email)).toBeVisible();
 
-    const customers = await (await request.get('/api/admin/customers')).json();
+    const customers: { id: number; email: string }[] = await (
+      await request.get('/api/admin/customers')
+    ).json();
     const id = findOrFail(
       customers,
-      (c: { email: string }) => c.email === customer.email,
+      (c) => c.email === customer.email,
       `the customer ${customer.email}`
     ).id;
     await request.post(`/api/admin/customers/${id}/disable`);
@@ -56,10 +58,12 @@ test.describe('Disabling a customer account', () => {
     authModal,
     header
   }) => {
-    const customers = await (await request.get('/api/admin/customers')).json();
+    const customers: { id: number; email: string }[] = await (
+      await request.get('/api/admin/customers')
+    ).json();
     const id = findOrFail(
       customers,
-      (c: { email: string }) => c.email === customer.email,
+      (c) => c.email === customer.email,
       `the customer ${customer.email}`
     ).id;
     await request.post(`/api/admin/customers/${id}/disable`);
diff --git a/frontend/tests/e2e/admin-inline-category.spec.ts b/frontend/tests/e2e/admin-inline-category.spec.ts
index 05997b4..e4a782b 100644
--- a/frontend/tests/e2e/admin-inline-category.spec.ts
+++ b/frontend/tests/e2e/admin-inline-category.spec.ts
@@ -31,12 +31,14 @@ test.describe('Inline category creation from the item form', () => {
     await adminInventory.confirmButton.click();
     await expect(page.getByText('Item added')).toBeVisible();
 
-    const items = await (await page.request.get('/api/admin/items')).json();
+    const items: { name: string; category_name: string | null }[] = await (
+      await page.request.get('/api/admin/items')
+    ).json();
     // findOrFail already fails with the row count when the item is missing,
     // which the toBeTruthy assertion this replaces could not report.
     const saved = findOrFail(
       items,
-      (item: { name: string }) => item.name === itemName,
+      (item) => item.name === itemName,
       `the item named ${itemName}`
     );
     expect(saved.category_name).toBe(categoryName);
diff --git a/frontend/tests/e2e/admin-taxonomy.spec.ts b/frontend/tests/e2e/admin-taxonomy.spec.ts
index 6896b67..bd6ace9 100644
--- a/frontend/tests/e2e/admin-taxonomy.spec.ts
+++ b/frontend/tests/e2e/admin-taxonomy.spec.ts
@@ -40,10 +40,12 @@ test.describe('Admin taxonomy', () => {
 
     // The table paginates and the shared database holds many tags, so the new
     // row is confirmed through the API rather than hunted for across pages.
-    const tags = await (await page.request.get('/api/admin/tags')).json();
+    const tags: { name: string; color: string | null }[] = await (
+      await page.request.get('/api/admin/tags')
+    ).json();
     const created = findOrFail(
       tags,
-      (tag: { name: string }) => tag.name === `vintage-${RUN}`,
+      (tag) => tag.name === `vintage-${RUN}`,
       `the tag vintage-${RUN}`
     );
     expect(created.color).toBeTruthy();
diff --git a/frontend/tests/e2e/email-templates.spec.ts b/frontend/tests/e2e/email-templates.spec.ts
index 416d872..48fac51 100644
--- a/frontend/tests/e2e/email-templates.spec.ts
+++ b/frontend/tests/e2e/email-templates.spec.ts
@@ -50,10 +50,12 @@ test.describe('Editing the customer emails', () => {
     await expect(page.getByText('Password reset saved')).toBeVisible();
 
     // Persisted, not merely accepted by the form.
-    const stored = await (await page.request.get('/api/admin/email-templates')).json();
+    const stored: { key: string; subject: string | null; body: string | null }[] = await (
+      await page.request.get('/api/admin/email-templates')
+    ).json();
     const reset = findOrFail(
       stored,
-      (t: { key: string }) => t.key === 'passwordReset',
+      (t) => t.key === 'passwordReset',
       'the passwordReset template'
     );
     expect(reset.subject).toBe(subject);
@@ -72,10 +74,12 @@ test.describe('Editing the customer emails', () => {
     await expect(page.getByText('the body must keep {{resetUrl}}')).toBeVisible();
 
     // And nothing was stored.
-    const stored = await (await page.request.get('/api/admin/email-templates')).json();
+    const stored: { key: string; subject: string | null; body: string | null }[] = await (
+      await page.request.get('/api/admin/email-templates')
+    ).json();
     const reset = findOrFail(
       stored,
-      (t: { key: string }) => t.key === 'passwordReset',
+      (t) => t.key === 'passwordReset',
       'the passwordReset template'
     );
     expect(reset.body).toBeNull();
@@ -95,10 +99,12 @@ test.describe('Editing the customer emails', () => {
 
     await expect(page.getByText('Password reset restored to the default')).toBeVisible();
 
-    const stored = await (await page.request.get('/api/admin/email-templates')).json();
+    const stored: { key: string; subject: string | null; body: string | null }[] = await (
+      await page.request.get('/api/admin/email-templates')
+    ).json();
     const reset = findOrFail(
       stored,
-      (t: { key: string }) => t.key === 'passwordReset',
+      (t) => t.key === 'passwordReset',
       'the passwordReset template'
     );
     expect(reset.subject).toBeNull();
@@ -124,10 +130,12 @@ test.describe('Previewing the customer emails', () => {
     // point: an admin sees the effect before committing to it.
     await expect(adminEmails.preview('Password reset').getByText(wording)).toBeVisible();
 
-    const stored = await (await page.request.get('/api/admin/email-templates')).json();
+    const stored: { key: string; subject: string | null; body: string | null }[] = await (
+      await page.request.get('/api/admin/email-templates')
+    ).json();
     expect(findOrFail(
       stored,
-      (t: { key: string }) => t.key === 'passwordReset',
+      (t) => t.key === 'passwordReset',
       'the passwordReset template'
     ).body).toBeNull();
   });
diff --git a/frontend/tests/e2e/favorites-filter.spec.ts b/frontend/tests/e2e/favorites-filter.spec.ts
index ed0c700..45a6040 100644
--- a/frontend/tests/e2e/favorites-filter.spec.ts
+++ b/frontend/tests/e2e/favorites-filter.spec.ts
@@ -178,10 +178,10 @@ test.describe('Filtering the storefront by favorites', () => {
     await favorite(storefront, favoritePrompt, SELLS);
 
     const api = await createAdminContext(playwright);
-    const items = await (await api.get('/api/items')).json();
+    const items: { id: number; name: string }[] = await (await api.get('/api/items')).json();
     const sells = findOrFail(
       items,
-      (item: { name: string }) => item.name === SELLS,
+      (item) => item.name === SELLS,
       `the item named ${SELLS}`
     );
     await sellItem(api, sells.id);
diff --git a/frontend/tests/e2e/support/findOrFail.ts b/frontend/tests/e2e/support/findOrFail.ts
index d971086..a21de5c 100644
--- a/frontend/tests/e2e/support/findOrFail.ts
+++ b/frontend/tests/e2e/support/findOrFail.ts
@@ -19,7 +19,14 @@
  */
 export function findOrFail<T>(
   items: T[],
-  predicate: (item: T) => boolean,
+  // NoInfer so the element type comes from `items` alone. Callers annotate the
+  // predicate parameter as documentation — `(c: { email: string }) => ...` — and
+  // without this the compiler would infer T from that annotation instead, so
+  // findOrFail would return the one-field shape written in the lambda rather
+  // than the row. Every caller then failed on the field it actually wanted:
+  // `.id does not exist on type { email: string }`. Array.prototype.find has no
+  // such problem, which is why the code this replaced type-checked.
+  predicate: (item: NoInfer<T>) => boolean,
   description: string
 ): T {
   const found = items.find(predicate);