fix(runtime): stabilize navigation and custom errors

packages/dev-server/src/runtime.ts

@@ -672,6 +672,25 @@ export const HMR_CLIENT_JS = `
     pendingSync = false;
     var doc = new DOMParser().parseFromString(html, "text/html");
 
+    var i18nScript = Array.prototype.find.call(
+      doc.querySelectorAll("script:not([src])"),
+      function (node) { return /^window\.__wrnI18n=/.test(String(node.textContent || "").trim()); },
+    );
+    if (i18nScript) {
+      var i18nMatch = /^window\.__wrnI18n=([\s\S]*);\s*$/.exec(String(i18nScript.textContent || "").trim());
+      if (i18nMatch) {
+        try {
+          var incomingI18n = JSON.parse(i18nMatch[1]);
+          var existingI18n = window.__wrnI18n || {};
+          incomingI18n.t = existingI18n.t;
+          incomingI18n.set = existingI18n.set;
+          window.__wrnI18n = incomingI18n;
+        } catch (error) {
+          console.error("[wrnexus] failed to synchronize i18n HMR data", error);
+        }
+      }
+    }
+
     if (doc.title) {
       document.title = doc.title;
     }
@@ -704,6 +723,10 @@ export const HMR_CLIENT_JS = `
       window.__wrnexusHydrateCsrFetches(document);
     }
 
+    if (window.__wrnLang && typeof window.__wrnLang.bind === "function") {
+      window.__wrnLang.bind(document);
+    }
+
     if (
       window.wrnTheme &&
       typeof window.wrnTheme.bind === "function"
@@ -1449,7 +1472,23 @@ export function createHandlers(deps: RuntimeDeps): Handlers {
 
   async function handleApi(ctx: Context): Promise<Response> {
     const matched = router.matchApi(ctx.url.pathname);
-    if (!matched) return Response.json({ error: "Not Found" }, { status: 404 });
+    if (!matched) {
+      const fallback = router.matchApi("/api/404");
+      if (fallback && ctx.url.pathname !== "/api/404") {
+        const originalPath = ctx.url.pathname;
+        ctx.url.pathname = "/api/404";
+        try {
+          const response = await handleApi(ctx);
+          return new Response(response.body, {
+            status: 404,
+            headers: response.headers,
+          });
+        } finally {
+          ctx.url.pathname = originalPath;
+        }
+      }
+      return Response.json({ error: "Not Found" }, { status: 404 });
+    }
 
     // Expose the canonical matched route to package dispatchers. A package may
     // contribute several URL paths from one module, and request URLs can be
@@ -1606,7 +1645,23 @@ export function createHandlers(deps: RuntimeDeps): Handlers {
           }),
         );
       }
-      const response = renderNotFound();
+      let response: Response;
+      const fallback = router.matchPage("/404");
+      if (fallback && ctx.url.pathname !== "/404") {
+        const originalPath = ctx.url.pathname;
+        ctx.url.pathname = "/404";
+        try {
+          const rendered = await handlePage(ctx);
+          response = new Response(rendered.body, {
+            status: 404,
+            headers: rendered.headers,
+          });
+        } finally {
+          ctx.url.pathname = originalPath;
+        }
+      } else {
+        response = renderNotFound();
+      }
       if (!isMobileRequest) return response;
       const headers = new Headers(response.headers);
       headers.set("x-wrnexus-original-status", "404");