fix: redirect should always return updated router state (#85533)
When a server action triggers a redirect, it will return the RSC payload
for the destination state in a single roundtrip. This lets us update the
UI without needing to waterfall when getting the target page's data. We
reject the server action with a special error signaling that the form
state should be reset, but otherwise the redirect itself is unnecessary,
since we already are handling it in the server action reducer.
However, when we introduced Activity for bfCache, this meant navigating
back to the previous page would replay the redirect error that was
stashed in the `RedirectBoundary`. I incorrectly patched this by just
returning the current router state, rather than the redirect
destination's state, but this lost the ability to return the updated
state in the same roundtrip as the redirect. Instead, this marks the
error that gets stashed in the `RedirectBoundary` as being "handled".
Re-activating the hidden subtree will now still correctly reset the
state (because the boundary handles it), but won't attempt to perform
the redirect again.
Closes NAR-470
next.js
1bca3db0 - fix: redirect should always return updated router state (#85533)
