Check if this issue is valid — if so, understand the root cause and fix it. At library/src/types/utils.ts, line 66:

<comment>`MarkOptional` drops explicitly declared keys hidden by an index signature. Remap the optional half over `TKeys` directly so `MarkOptional<{ [key: string]: unknown; type: 'foo' }, 'type'>` still enforces `type?: 'foo'`.</comment>

<file context>
@@ -60,10 +60,11 @@ export type Prettify<TObject> = { [TKey in keyof TObject]: TObject[TKey] } & {};
+export type MarkOptional<TObject, TKeys extends keyof TObject> = {
+  [TKey in keyof TObject as TKey extends TKeys ? never : TKey]: TObject[TKey];
+} & {
+  [TKey in keyof TObject as TKey extends TKeys ? TKey : never]?: TObject[TKey];
+};
 
</file context>

Check if this issue is valid — if so, understand the root cause and fix it. At library/src/types/utils.ts, line 64:

<comment>This reimplementation intentionally changes the displayed key order of `Prettify`-wrapped output types (required keys now precede optional ones, e.g. `{ id: number; name: string; email?: string }`), but neither the code nor the CHANGELOG entry records the trade-off, and the comment explaining key-order preservation was deleted. Because `toEqualTypeOf` ignores key order, the test suite cannot catch this user-visible change to hover previews and docs. Add a comment above `MarkOptional` documenting the required-before-optional ordering, and if the order change is accepted, reflect it in the CHANGELOG entry.</comment>

<file context>
@@ -60,10 +60,11 @@ export type Prettify<TObject> = { [TKey in keyof TObject]: TObject[TKey] } & {};
-  { [TKey in keyof TObject]?: unknown } & Omit<TObject, TKeys> &
-    Partial<Pick<TObject, TKeys>>;
+export type MarkOptional<TObject, TKeys extends keyof TObject> = {
+  [TKey in keyof TObject as TKey extends TKeys ? never : TKey]: TObject[TKey];
+} & {
+  [TKey in keyof TObject as TKey extends TKeys ? TKey : never]?: TObject[TKey];
</file context>

Check if this issue is valid — if so, understand the root cause and fix it. At library/CHANGELOG.md, line 7:

<comment>This PR changes how inferred object types are displayed for every schema with optional entries: required keys are now shown before optional keys (e.g. `{ id: number; name: string; email?: string }` vs the original declaration order), because `Prettify` resolves the two key-remapped members in intersection order and the old `{ [TKey in keyof TObject]?: unknown }` order-preserving member is gone. Since the old comment documented that member as existing precisely to preserve key order, record this user-visible display change in the CHANGELOG entry (or keep the order-preserving member) so the decision called for in the PR is explicit.</comment>

<file context>
@@ -4,6 +4,7 @@ All notable changes to the library will be documented in this file.
 
 ## vX.X.X (Month DD, YYYY)
 
+- Change `MarkOptional` type to use key remapping instead of `Omit`, `Pick` and `Partial` to improve TypeScript performance (pull request #1675)
 - Change internal `VariantOption` and `VariantOptionAsync` types of `variant` schema to use a structural object option type to improve TypeScript performance (pull request #1670)
 - Change `isbn`, `creditCard` and `imei` actions to check digits by character code instead of splitting and parsing the input to improve performance (pull request #1634)
</file context>