Main centralised the launch gate in structured-native-chat-launch-route, where it
re-added the client-side codex+win32 refusal. Delete that blocker there instead,
so the renderer and orchestration both stop guessing; createSupport still answers.
Drops the now-unread platform input end to end.
Also dedupes two shadowed lastActivityAt keys that arrived from main in #19127 and
fail tsc; the later value already won, so behaviour is unchanged.