Both useChat (full ChatView) and useQuickChat (FAB) loaded only the first 50
messages on open and never paginated further. In useChat, loadMoreMessages
exists but ChatView never calls it — dead code. In useQuickChat, there was
no pagination at all.
Fix: add fetchAllMessagesInChat / fetchAllMessages helpers (paginate through
the API 200-msg cap), replace all limit:50 initial-load call sites, and
add stale-session guards via activeSessionRef before calling setMessages.
hasMoreMessages is set to false after a full initial load.
Forward-pagination path in useChat (isPaginationRequest=true) is preserved
for backward compat.
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