* feat(native-chat): record a fresh provider conversation that replaced one the agent could not restore
A chat whose saved conversation the agent cannot reopen can now continue in a
fresh one: the handle chain records the new conversation as a creation that
replaces the lost one (which, why, and when), keeping every earlier link.
Rows keep a shape older builds read: the stored chain starts at the latest
replacement and carries the earlier links inside it.
* refactor(native-chat): store a replaced conversation flat; refuse it where older builds read the row
Older builds only read Claude and Codex records, so the nested stored form
protected rows no replacement can reach while adding a cap mismatch after a
downgrade. Store the chain as held, refuse a replacement in a Claude or Codex
chain until one has a stored shape older builds read, and refuse a supersession
key on a replacement that names no creation in the chain.
* test(native-chat): prove replacement rows survive downgrade and re-upgrade
Brennan Benson
eaaae0196f