next.js

ba70eda3 - Revert "Respond with `404` for unknown server actions (#80613)" (#80662)

Revert "Respond with `404` for unknown server actions (#80613)" (#80662) @unstubbable and i independently worked on fixing the same bug, but my solution got a bit further along + i have a stack of other changes on top, so we're going to do mine instead. - #77012 implements equivalent functionality for fetch actions (but more efficiently, because it skips rendering the 404 HTML, and with a better error message) - #77014 also fixes the error message for MPA actions, but unlike the reverted PR, it _doesn't_ make them return a 404 html page -- that's not semantically correct, because an unrecognized action error is fixed by a refresh. - #78933 allows handling this error on the client