Crinja::Template

=== 8. Presized page buffer ========================================== Template#render(bindings) builds its result with a default String.build, which starts at 64 bytes and doubles. A 400 KB page therefore reallocates about thirteen times and memcpys roughly twice its own size before it is finished — per page, on every page.

Consecutive renders of the SAME template produce similarly sized output (a listing page is a listing page), so the previous render's size is a good capacity hint. It is only a hint: too small and String::Builder grows exactly as it does today, too large and the final String.build trims the excess. No byte of output depends on it.

@render_size_hint is an aligned Int32 shared between render workers, so a concurrent write cannot tear — the worst case is a worker reading a size from a different page, which is the same class of estimate the value is.