[Hot Reload] Enable hot reloading for Blazor inside an iframe

[jsakamoto]

Description

Hot Reload on a Blazor app doesn't work inside an iframe. See the attached video and sample code.

2024-02-29_08h08_22.mp4

Sample code: 📦BlazorWasmApp1.zip

The solution I'd like

I know this is intentional by design, as mentioned in the pull request: dotnet/sdk#21954. However, some edge cases exist where hot reloading support inside an iframe is essential. For instance, the clone of Storybook for Blazor, "Blazing Story" (https://github.com/jsakamoto/BlazingStory), requires such ability because it has to host a preview of the story using an iframe.

Therefore, I hope we have a public "escape hatch" API allowing developers to explicitly enable hot reloading inside an iframe for such a particular scenario.

[jsakamoto]

Related Feature Requests

See also: #39153 [Hot Reload] Enable Blazor hot reloading for multiple browser windows at the same time

The ability above is also required for the hot reloading on the "Blazing Story".

[MackinnonBuck]

We might be able to address this in one of two ways:

1. Update this line to include the "frame" and "iframe" values for the Sec-Fetch-Dest header.
2. Address this as part of Revisit hot reload browser refresh script injection #45213