Retain partial-line output, UTF-8 decoding, failure output and cancellation cleanup. Based on streaming investigations by Artemonim (#101850) and lEWFkRAD (#104843); gateway tee adapted from fangliquanflq (#97402). Live Linux child/tee probe: withheld or dropped on base, visible in 0.02 seconds after. Campaign-locked tests and native Windows proof are pending.
