stacklok / toolhive-studio / 24769501795

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feat(playground): preload thread in the route loader and delegate scroll restoration to router (#2062)

* feat(playground): redirect to initial thread in beforeLoad

Resolve the target thread in the router's beforeLoad and throw redirect()
instead of mounting a component that runs the resolution in a useEffect.
Eliminates the one-frame blank render between /playground and the
chat sub-route.

* feat(playground): prime thread data via route loader and React Query

Introduce chatThreadQueryOptions and consume it from the
/playground/chat/$threadId loader via ensureQueryData + pendingComponent.
useChatStreaming reads messages from the cache with useQuery and hydrates
the useChat instance once per thread via a ref guard, so switching
threads no longer flashes a loading state. usePlaygroundThreads
invalidates the new query key on streaming-complete to refresh titles
and messages. Remove the now-unused loadMessages from
useThreadManagement.

* refactor(chat): delegate chat scroll restoration to TanStack Router

Enable router-level scrollRestoration keyed by location.pathname and
register the chat messages container with data-scroll-restoration-id so
TSR persists and restores its scroll position across navigations. Apply
overflow-anchor: auto on the scroll container and each MCP app iframe
wrapper so async height changes don't shove the viewport.

useAutoScroll is rewritten around the new contract: its responsibilities
shrink to following the bottom while streaming, the scroll-to-bottom
button, and an initial 5s settling window that re-applies the saved
scroll target as MCP iframes finish their size handshake. Distinguishes
overflow-anchor-driven scroll events from genuine user input (wheel /
touch / key / pointer) so the settling window isn't cancelled by the
first iframe resize. The in-component loading overlay is removed — the
route's pendingComponent now owns that state.

* fix(chat): restore scroll position when user was at the top

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