docs(sdks): document exactOptionalPropertyTypes TypeScript generator option

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

Author: devin-ai-integration[bot]

fern/products/sdks/generators/typescript/configuration.mdx

@@ -88,6 +88,18 @@ const bar: MyRootType.Foo.Bar = {};
 ```
 </ParamField>
 
+<ParamField path="exactOptionalPropertyTypes" type="boolean" default="false" toc={true}>
+When enabled, every optional property in the generated SDK is emitted as `prop?: T | undefined`, and the generated `tsconfig` files enable TypeScript's [`exactOptionalPropertyTypes`](https://www.typescriptlang.org/tsconfig/#exactOptionalPropertyTypes) compiler option. This covers model types, inlined request types, client options, errors, and the `core/` utilities, so consumers whose own `tsconfig` sets `exactOptionalPropertyTypes: true` can use the SDK without type errors.
+
+This option applies with or without the serde layer, so it can be combined with either value of [`noSerdeLayer`](#noserdelayer).
+
+```yaml
+# generators.yml
+config:
+  exactOptionalPropertyTypes: true
+```
+</ParamField>
+
 <ParamField path="extraDependencies" type="object" default="{}" toc={true}>
 
 <Markdown src="/snippets/enterprise-plan.mdx"/>