Advice on loss of blazor.boot.json (#35535)

Author: guardrex

aspnetcore/blazor/host-and-deploy/webassembly/bundle-caching-and-integrity-check-failures.md

@@ -20,7 +20,10 @@ When a Blazor WebAssembly app loads in the browser, the app downloads boot resou
 * .NET runtime and assemblies
 * Locale specific data
 
-Except for Blazor's boot manifest file (`blazor.boot.json` ) prior to the release of .NET 10, WebAssembly .NET runtime and app bundle files are cached on clients. The Blazor boot configuration, inlined into `dotnet.js` in .NET 10 or later, contains a manifest of the files that make up the app that must be downloaded along with a hash of the file's content that's used to detect whether any of the boot resources have changed. Blazor caches downloaded files using the browser [Cache](https://developer.mozilla.org/docs/Web/API/Cache) API.
+Except for Blazor's boot manifest file (`blazor.boot.json`) prior to the release of .NET 10†, WebAssembly .NET runtime and app bundle files are cached on clients. The Blazor boot configuration, inlined into `dotnet.js` in .NET 10 or later, contains a manifest of the files that make up the app that must be downloaded along with a hash of the file's content that's used to detect whether any of the boot resources have changed. Blazor caches downloaded files using the browser [Cache](https://developer.mozilla.org/docs/Web/API/Cache) API.
+
+> [!NOTE]
+> †If upgrading an app to .NET 10 or later and the app relies on the `blazor.boot.json` manifest file for custom processing, we recommend collecting the information directly from the build.
 
 When Blazor WebAssembly downloads an app's startup files, it instructs the browser to perform integrity checks on the responses. Blazor sends SHA-256 hash values for DLL (`.dll`), WebAssembly (`.wasm`), and other files in the Blazor boot configuration, which isn't cached on clients. The file hashes of cached files are compared to the hashes in the Blazor boot configuration. For cached files with a matching hash, Blazor uses the cached files. Otherwise, files are requested from the server. After a file is downloaded, its hash is checked again for integrity validation. An error is generated by the browser if any downloaded file's integrity check fails.