Direct links not working properly with embedded clients

[dwhly]

Problem

Presently, bouncer is not able to detect that H is embedded on any given target page. It can only detect when the browser extension is present. Therefore, it cannot pass the direct link context (annotation, users, etc) to the embedded client.

This becomes particularly important when the client is embedded in particular ways, such as within subframes.

For instance, this annotation https://hyp.is/Crgo6IziEei8ikdTuMpbWg/osf.io/preprints/socarxiv/32n8y/
Links to an annotation on a COS preprint. The preprint PDF is embedded w/ H in a subframe on that page. But if you follow the direct link it will link instead to a random period at the bottom of the page.

This is a two level problem. It needs to work both when the user has the browser extension and when they don't (and typically we would route thru the proxy service).

Acceptance Criteria

Direct links (encoded w/ bouncer) need a way to be routed to embedded clients.

[dwhly]

Also, of course, what do we do when a user has annotated something on the page outside of the embedded content and wants to return there / share the location via a direct link. So some links will want to take the user back to the embedded content, some will want to take the user back to the surrounding non-embedded content. Perhaps this gets back to us storing whether the original annotation was made within a subframe or not-- brittle as that might be?

[ajpeddakotla]

Business Viability	User Engagement	Building Community	Level of Effort
2	3	3	2

[mkdir-washington-edu]

See also:

• If Bouncer does not detect the Chrome extension it defaults to Via even if Hypothesis is embedded on the page support-legacy#151
• Direct links don't work (reliably?) if target page embeds the client browser-extension#1355