Walking-Skeleton Pre-Flight Decisions — Augment-It Rewrite

Five decisions that have to be settled before we can write code for the augment-it rewrite. Captured here as a single load-bearing doc so a future session can pick up the build without re-walking the decision tree in chat. State management is hand-rolled useSyncExternalStore. Transport is HTTP fetch to a bun sidecar at localhost. Persistence is JSON files written by the sidecar; graduate to libSQL when multi-device demands it. Auth is opaque session tokens auto-minted by the sidecar on first contact — real user_ids and sessions without an OAuth detour. The @lossless/in-app-agent scaffolding question remains open pending a final call on whether augment-it drives the package's first implementation.