docs: add docs for @switch Exhaustive type checking

(cherry picked from commit 9dc3ca44ec)

adev/src/content/guide/templates/control-flow.md

@@ -133,3 +133,30 @@ You can specify multiple conditions for a single block by have consecutive `@cas
 You can optionally include a `@default` block. The content of the `@default` block displays if none of the preceding case expressions match the switch value.
 
 If no `@case` matches the expression and there is no `@default` block, nothing is shown.
+
+### Exhaustive type checking
+
+`@switch` supports exhaustive type checking, allowing Angular to verify at compile time that all possible values of a union type are handled.
+
+By using `@default never;`, you explicitly declare that no remaining cases should exist. If the union type is later extended and a new case is not covered by an @case, Angular’s template type checker will report an error, helping you catch missing branches early.
+
+```angular-html
+@Component({
+  template: `
+    @switch (state) {
+      @case ('loggedOut') {
+        <button>Login</button>
+      }
+
+      @case ('loggedIn') {
+        <p>Welcome back!</p>
+      }
+
+      @default never; // throws because `@case ('loading')` is missing
+    }
+  `,
+})
+export class AppComponent {
+  state: 'loggedOut' | 'loading' | 'loggedIn' = 'loggedOut';
+}
+```

tools/manual_api_docs/blocks/switch.md

@@ -30,3 +30,30 @@ You can specify multiple conditions for a single block by having consecutive `@c
 
 **`@switch` does not have fallthrough**, so you do not need an equivalent to a `break` or `return`
 statement.
+
+### Exhaustive type checking
+
+`@switch` supports exhaustive type checking, allowing Angular to verify at compile time that all possible values of a union type are handled.
+
+By using `@default never;`, you explicitly declare that no remaining cases should exist. If the union type is later extended and a new case is not covered by an @case, Angular’s template type checker will report an error, helping you catch missing branches early.
+
+```angular-html
+@Component({
+  template: `
+    @switch (state) {
+      @case ('loggedOut') {
+        <button>Login</button>
+      }
+
+      @case ('loggedIn') {
+        <p>Welcome back!</p>
+      }
+
+      @default never; // throws because `@case ('loading')` is missing
+    }
+  `,
+})
+export class AppComponent {
+  state: 'loggedOut' | 'loading' | 'loggedIn' = 'loggedOut';
+}
+```