docs(sdks): document exactOptionalPropertyTypes TypeScript generator option

[devin-ai-integration]

TypeScript teams that turn on the exactOptionalPropertyTypes compiler option previously couldn't consume a Fern-generated SDK without type errors, and some were hand-writing .d.ts files to work around it. The TypeScript SDK generator now has an opt-in exactOptionalPropertyTypes config option that emits every optional property as prop?: T | undefined and enables the same compiler option in the generated tsconfig, so the SDK typechecks cleanly under the stricter mode. This documents the option on the TypeScript configuration reference, including that it works with or without the serde layer.

Implements docs for: feat(typescript): add exactOptionalPropertyTypes generator option (fern-api/fern#17697) — fern-api/fern#17697

Summary

Pages changed:

• fern/products/sdks/generators/typescript/configuration.mdx — new <ParamField path="exactOptionalPropertyTypes" type="boolean" default="false"> entry, placed alphabetically between enableInlineTypes and extraDependencies, with a generators.yml example and a cross-link to noSerdeLayer.

No SDK changelog entry (auto-generated) and no translation edits.

Validation: pre-commit run --files on the changed file (the two Vale errors it reports are pre-existing lines 22 and 599) and fern check --warnings (0 errors).

Link to Devin session: https://app.devin.ai/sessions/4b05774ba68f4d66801e53450a759028
Open in Devin Desktop: https://app.devin.ai/desktop/session/4b05774ba68f4d66801e53450a759028?variant=devin

[devin-ai-integration]

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[github-actions]

🌿 Preview your docs: https://fern-preview-devin-1789146316-ts-exact-optional-property-types.docs.buildwithfern.com/learn

Here are the markdown pages you've updated:

• learn/sdks/generators/typescript/configuration