True when arr is exactly the bottom-right-aligned causal matrix
(offset continuation, no window) — the case where mlx-lm would
have handed the string "causal" instead. Only these array masks
are eligible for the fused tiled SDPA: the optiq wrapper falls
back to unfused on every array mask, and window/bidir masks must
match that to stay scenario-bit-exact.
True when
arris exactly the bottom-right-aligned causal matrix (offset continuation, no window) — the case where mlx-lm would have handed the string "causal" instead. Only these array masks are eligible for the fused tiled SDPA: the optiq wrapper falls back to unfused on every array mask, and window/bidir masks must match that to stay scenario-bit-exact.