Adversarial review F7 (Low, confirmed): the Step-2 Output::Timeout arm
checked `needs_redrain` but the flag could only be set inside Step 3
(which runs after Step 2 exits). The arm was unreachable dead code that
misled readers into thinking Step 2 re-drains inter-iteration.
The flag itself remains load-bearing for the bottom re-drain after
Step 3's Writer::write (str0m's mutation → drain-to-Timeout invariant).
Only the inner-loop check is removed; production behavior unchanged.
Refactor phase — existing tests stay green.
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