fix(types): preserve named properties in processed options

type-tests/processed-options.ts

@@ -0,0 +1,17 @@
+import type HtmlRspackPlugin from '../typings';
+
+type Equal<A, B> =
+  (<T>() => T extends A ? 1 : 2) extends <T>() => T extends B ? 1 : 2
+    ? true
+    : false;
+type Assert<T extends true> = T;
+
+type Options = HtmlRspackPlugin.Options;
+type ProcessedOptions = HtmlRspackPlugin.ProcessedOptions;
+
+// Runtime tests cannot detect options degrading to any. Check a named option
+// and keep minify optional to guard against regressions in ProcessedOptions.
+export type ProcessedOptionsAssertions = [
+  Assert<Equal<ProcessedOptions['title'], string>>,
+  Assert<Equal<Pick<ProcessedOptions, 'minify'>, Pick<Options, 'minify'>>>,
+];

typings.d.ts

@@ -171,8 +171,10 @@ declare namespace HtmlRspackPlugin {
   /**
    * The plugin options after adding default values
    */
-  type ProcessedOptions = Required<Omit<Options, 'minify'>> &
-    Pick<Options, 'minify'>;
+  type ProcessedOptions = {
+    // Preserve named properties alongside the index signature in Options.
+    [K in keyof Options as Exclude<K, 'minify'>]-?: Options[K];
+  } & Pick<Options, 'minify'>;
 
   /**
    * The values which are available during template execution