The first compile this branch had. One borrow error, in the four-thread
contention test: the `Runner` was the block's tail expression, and a
tail's temporaries are dropped after the block's locals, so it outlived
the `conn` it borrowed. Bound to a local, with the ordering rule written
down beside it -- it is exactly the shape someone tidies back.
Everything else stood: clippy clean at -D warnings, and all 18 runner
tests pass, including the four-thread four-connection claim and the
`UPDATE ... RETURNING` rewrite the author flagged as the riskiest line
in the diff.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>