LogTeeSink typedef
LogTeeSink =
void Function(String text)
Writes one teed chunk — exactly the text the CLI produced, writeln
chunks already carrying their trailing newline. The executable wires
this to an unbuffered file sink (bin/fah.dart owns dart:io), so
every chunk reaches the OS as it is produced and a tail -f on the
log streams the trace live.
Implementation
typedef LogTeeSink = void Function(String text);