feat: Add optional attention_mask input to LTXVAddGuide (CORE-220)

[drozbay]

LTXVAddGuide gets an optional attention_mask input, matching the attention_mask input on Lightricks's LTXAddVideoICLoRAGuideAdvanced custom node from ComfyUI-LTXVideo. It is a pixel-space mask that controls per-region conditioning influence, multiplied by the node's existing strength. With nothing connected, behavior is unchanged.

The LTXV model code already reads each guide's pixel_mask and applies it when weighting that guide's self-attention.

Workflow for testing:

This example shows using a temporally fading attention mask to allow smoother transitions for first and last frame inputs when combined with IC-lora control.
(Uses ComfyUI-KJNodes for Fade Mask)

droz_LTX23_attention_mask_example_v1.json

Expected output:

ComfyUI_00126_.mp4

Input assets for test workflow:

input_assets.zip

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• comfy_extras/nodes_lt.py

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📝 Walkthrough

Walkthrough

This PR adds an optional attention_mask input to LTXVAddGuide and threads it through LTXVAddGuide.execute into _append_guide_attention_entry. When provided, attention_mask is unsqueezed to a (1,1,F,H,W)-compatible pixel_mask per guide entry; otherwise pixel_mask is None. A comment clarifies guide entries are shallow-copied and pixel_mask is not mutated.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 25.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and specifically describes the main change: adding an optional attention_mask input to the LTXVAddGuide node, with a relevant ticket reference.
Description check	✅ Passed	The description is directly related to the changeset, explaining the purpose of the attention_mask input, its integration with existing functionality, and providing testing examples and assets.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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