Only TypeScript, shell, and JSON grammars load at Web boot; the read card's
wider langFromPath extension set loads through dynamic imports on first use,
so a session that never opens a read card in one of those languages avoids
~1.6 MB of grammar modules and their synchronous init. ReadBlock/CodeBlock
re-render on grammar-load via useSyncExternalStore, picking up highlighting
once the grammar registers. ReadBlock hides the copy control on an empty
window (a successful read of an empty file settles to lines: [] with
card:'read'), matching TerminalBlock so it cannot wipe the clipboard.
Chinesezjc
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