Splits 'Preserve Session on Restart' into the two problems it actually is.

The login half is located: the cookie is a pointer into an in-memory Map in
the CLI's auth (auth.ts:164), so a restart leaves a valid cookie resolving to
nothing — which is why it reads as 'cookies reset' when the cookie is fine.

The session half is the one worth not starting wrong. The durable SessionStore
already exists and is wired, but it is gated on Runner.park(), and grepping
that shows AiSdkRunner is the only implementation — so for claude and codex the
whole path is inert, and any plan beginning 'park everything on SIGTERM'
preserves provider sessions only. The brief points at rehydrate-via-engine-
resume instead, and lists the four questions to settle before writing code.