Port mechanisms 1+3 of SCAIL-2 (arXiv:2606.10804) to LTX-2: concatenate a
driving video latent directly into the DiT token sequence with a width-axis
RoPE offset (ΔW) so driving coords stay detached from the target video.
- New VideoConditionByDrivingLatent + DrivingMode in ltx-core conditioning,
modeled on VideoConditionByReferenceLatent (patchify -> positions -> append
-> attention mask). Applies ΔW width shift, aligns time to the target, and
guards against RoPE wrap (max_pos) and target/driving shape mismatch.
- Export both from conditioning packages.
- docs/plan.md and docs/tasks.md track the phased port.
Inference-only: no weight changes. Mechanism 2 (in-context mask channels,
patchify_proj widening) and training are deferred to Phase 2+. Validated via
plumbing checks and a real (random-weight) transformer forward smoke run;
visual quality is not validated (requires Phase 2/3 finetuning).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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