fix(app-error): auto-recover from stale-shell ChunkLoadError

After a deploy the cached SPA shell still references the old chunk
filenames. Next.js fetches them, the new server 404s the request,
and the user sees the generic error surface — typically with no
context other than "Failed to load chunk". The fix on the user's
side is a hard reload; before this commit they had to discover it
themselves.

`AppError` now detects the chunk-load family of errors
(`ChunkLoadError`, `Loading chunk`, `Failed to load chunk`,
`Failed to fetch dynamically imported module`) and triggers a single
`window.location.reload()`. `sessionStorage` gates the auto-reload
to once per session so an unrecoverable error doesn't loop into a
reload storm. Browsers in strict-privacy mode fall through to the
error UI cleanly.

src/app/error.tsx

@@ -3,6 +3,19 @@
 import { useEffect } from "react";
 import { ErrorDetails } from "@/components/error-details";
 
+const CHUNK_RELOAD_KEY = "healthlog:chunk-reload-attempted";
+
+function isChunkLoadError(err: Error & { digest?: string }): boolean {
+  if (err.name === "ChunkLoadError") return true;
+  const msg = err.message ?? "";
+  return (
+    msg.includes("Loading chunk") ||
+    msg.includes("Loading CSS chunk") ||
+    msg.includes("Failed to load chunk") ||
+    msg.includes("Failed to fetch dynamically imported module")
+  );
+}
+
 export default function AppError({
   error,
   reset,
@@ -18,6 +31,25 @@ export default function AppError({
       };
       g.__healthlog_onError?.(error);
     }
+
+    // v1.4.38.3 — auto-recover from a stale-shell chunk-load error.
+    // After a deploy the cached shell still references old chunk
+    // filenames; they 404 and Next.js surfaces them as `ChunkLoadError`.
+    // A single hard reload fetches the new shell + chunk graph.
+    // sessionStorage gates the auto-reload so an error we can't recover
+    // from (e.g. the new build is also missing the chunk) doesn't loop.
+    if (typeof window !== "undefined" && isChunkLoadError(error)) {
+      try {
+        const already = window.sessionStorage.getItem(CHUNK_RELOAD_KEY);
+        if (!already) {
+          window.sessionStorage.setItem(CHUNK_RELOAD_KEY, String(Date.now()));
+          window.location.reload();
+        }
+      } catch {
+        // sessionStorage can throw under strict privacy modes — fall
+        // through to the error UI in that case.
+      }
+    }
   }, [error]);
 
   return <ErrorDetails error={error} reset={reset} />;