Review follow-up on the concurrent-tool deadline salvage. timed_out_indices is
snapshotted from not_done at the deadline; a worker can still finish and write
results[i] in the window before the post-execution result loop reads it. The
loop unconditionally replaced results[i] with a fabricated 'timed out' message
for any snapshotted index, discarding a genuinely-successful (just-late) result.
Gate the timeout message on 'and r is None' so a real result always wins. Add a
regression test that forces the snapshot-vs-result-loop race deterministically
(mutation-checked: reverting the guard fails it). Also document the intentional
detached-worker leak at the executor abandon site.
