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.
Consume the card:'read' result view (path, numbered lines, totalLines, lang)
the read backend PR added. ReadBlock (ui-primitives) draws a per-line gutter
with each line's own file number, shiki highlighting via a new highlightLines
returning per-line token arrays, a 显示 X / Y 行 window note, a height cap
matching TerminalBlock, and a copy control. read-card-model is the single
resultView derivation; a keyed ReadRow registers under read with the card
resident under its path-link summary. The generic fallback and the details
panel are read-aware. Fixture gains a windowed read turn for the built-boot
snapshot.
