### What?
When handling a server action, in the non-progressive enhanced case,
React will attempt to parse the request body before verifying if a valid
server action is received. This results in an "Error: Connection Closed"
error being thrown, rather than ignoring the action and failing more
gracefully
### Why?
To support progressive enhancement with form actions, the `actionId`
value is added as a hidden input in the form, so the action ID from the
header shouldn't be verified until determining that we've reached the
non-PE case. ([React
ref](https://github.com/facebook/react/pull/26774)). However, in
https://github.com/vercel/next.js/pull/49187, support was added for a
URL encoded form (which is not currently used, as indicated on the PR).
Despite it not being used for server actions, it's currently possible to
trigger this codepath, ie by calling redirect in an action handler with
a 307/308 status code with some data in the URL. This would result in a
500 error.
### How?
React should not attempt to parse the URL encoded form data until after
we've verified the server action header for the non-PE case.
x-ref NEXT-1733
[Slack
context](https://vercel.slack.com/archives/C03S8ED1DKM/p1700674895218399?thread_ts=1700060786.749079&cid=C03S8ED1DKM)
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