A slice-streamed sentinel's wire base was bounds-checked (in range, below
the final block) but never validated to TILE the AU: a base that lied
within bounds left a zero gap and an overlap, and the reassembler still
stamped the frame `complete`. The decoder then painted the wrong-offset
bytes as garbage rectangles while no loss counter moved — so the recovery
machinery never fired and the corruption marched on indefinitely (the
field report: black bars 'moving like an equalizer', identical across
Vulkan/DXVA/CPU decoders, Android immune because it never negotiates the
slice wire).
At completion, verify the blocks tile [0..total_data] contiguously; a
frame that doesn't is killed exactly like a lying final header — index
remembered against stragglers, counted into frames_dropped, which is the
signal that arms the freeze gate and requests recovery. The
slice-progressive prefix walk gets the same contiguity guard so a lying
base can't extend a 'contiguous' prefix either.
enricobuehler