fix: types for return of mounted templates

Author: DylanPiercey

.changeset/major-shrimps-play.md

@@ -0,0 +1,5 @@
+---
+"@marko/runtime-tags": patch
+---
+
+Fix types for return of mounted templates.

packages/runtime-tags/index.d.ts

@@ -46,8 +46,19 @@ declare global {
       };
 
     /** The result of calling `template.mount`. */
-    export type MountedTemplate<Input = unknown, Return = unknown> = {
-      value: Return;
+    export type MountedTemplate<
+      Input = unknown,
+      Return extends void | {
+        value: unknown;
+        valueChange?(next: unknown): void;
+      } = void,
+    > = {
+      get value(): Return extends { value: infer Value } ? Value : void;
+      set value(
+        next: Return extends { valueChange?(next: infer Next): any }
+          ? Next
+          : never,
+      ): void;
       update(input: Marko.TemplateInput<Input>): void;
       destroy(): void;
     };
@@ -74,7 +85,13 @@ declare global {
       B extends Body<infer Params, any> ? Params : never;
 
     /** The top level api for a Marko Template. */
-    export abstract class Template<Input = unknown, Return = unknown> {
+    export abstract class Template<
+      Input = unknown,
+      Return extends void | {
+        value: unknown;
+        valueChange?(next: unknown): void;
+      } = void,
+    > {
       /**
        * The folowing types are processed up by the @marko/language-tools
        * and inlined into the compiled template.