Loading an older page prepends hundreds of messages in one flush. tap's
scheduler aborts after 50 dirty resources and drops the overflow, so the
thread never applied the merged page: the scroll-restore gate never
passed and the top sentinel kept re-triggering (loads everything at
once). Raise MAX_FLUSH_LIMIT 50->2000 via bun patchedDependencies.
Adds a Playwright regression spec driving the real message-window store
and HappyThread against a fake paginated API: one page per top
approach, scroll restored, no idle reloads.
