The multi-line retry checkout command ended with a newline, so splicing it
into '{checkout_command} &&' left a lone '&&' on the line after 'done' — a
bash syntax error failing every PR-triggered shard before checkout. End the
f-string at 'done' so the composed script reads 'done &&'; verified all four
compositions (PR/direct x kernel/no-kernel) with bash -n.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
