address review: clarify hmrClientEntry is a presence marker, not a path

Reword JSDoc and inline comment to make it explicit that only the
presence of hmrClientEntry matters — the value itself is not read by
any consumer, so assigning clientEntry to it is intentional marker
semantics, not a real path reference.

Author: bartlomieju

packages/fresh/src/build_cache.ts

@@ -18,9 +18,9 @@ export interface BuildSnapshot<State> {
   version: string;
   clientEntry: string;
   /**
-   * Pathname for an HMR-only client entry. When defined, the SSR runtime
-   * always emits the boot script so HMR listeners attach to pages that
-   * have no islands. Undefined outside of dev.
+   * When defined, forces the boot script to be emitted in dev so HMR
+   * listeners attach even on island-free pages. The value itself is
+   * currently unused — only its presence matters. Undefined outside of dev.
    */
   hmrClientEntry?: string;
   fsRoutes: FsRouteFile<State>[];

packages/plugin-vite/src/plugins/server_snapshot.ts

@@ -170,11 +170,12 @@ export function serverSnapshot(options: ResolvedFreshViteConfig): Plugin[] {
           const entryAssets: string[] = [];
 
           if (isDev && server !== undefined) {
-            // The client entry hosts the HMR listener. Set hmrClientEntry so
-            // the SSR runtime always emits a boot script in dev, even when
-            // a page has zero islands. Without this, edits to islands-free
-            // routes never trigger a browser reload because the
-            // `fresh:reload` WebSocket listener is never attached.
+            // Set hmrClientEntry so the SSR runtime always emits a boot script
+            // in dev, even when a page has zero islands. Without this, edits
+            // to island-free routes never trigger a browser reload because the
+            // `fresh:reload` WebSocket listener is never attached. The value
+            // is used as a marker only — its presence is what matters, not
+            // what it points to.
             hmrClientEntry = clientEntry;
 
             for (const id of islands.keys()) {