Z-Image LoRAs with only fused attention_qkv + attention_out keys are dropped, then fail on leftover alpha keys #14876

Describe the bug

A Z-Image LoRA that only carries the model's original attention module names, a fused attention_qkv and a bare attention_out per block (what musubi-tuner and LyCORIS emit when trained against the original Z-Image module layout), cannot be loaded: _convert_non_diffusers_z_image_lora_to_diffusers drops both keys on the assumption that split to.q/k/v and to_out.0 keys are also present (the Anime-Z layout, where they are redundant), which empties the LoRA, and then raises ValueError: state_dict should be empty on the leftover .alpha keys of the out modules.

Expected: the fused qkv LoRA is split into to_q / to_k / to_v (chunks of the up weight along dim 0, like convert_z_image_fused_attention does for base weights) and out maps to to_out.0.

Reproduction

import torch
from diffusers.loaders.lora_conversion_utils import _convert_non_diffusers_z_image_lora_to_diffusers

rank, dim = 2, 8
sd = {}
for block in ("layers_0", "context_refiner_0"):
    sd[f"lora_unet_{block}_attention_qkv.lora_down.weight"] = torch.randn(rank, dim)
    sd[f"lora_unet_{block}_attention_qkv.lora_up.weight"] = torch.randn(3 * dim, rank)
    sd[f"lora_unet_{block}_attention_qkv.alpha"] = torch.tensor(float(rank))
    sd[f"lora_unet_{block}_attention_out.lora_down.weight"] = torch.randn(rank, dim)
    sd[f"lora_unet_{block}_attention_out.lora_up.weight"] = torch.randn(dim, rank)
    sd[f"lora_unet_{block}_attention_out.alpha"] = torch.tensor(float(rank))

_convert_non_diffusers_z_image_lora_to_diffusers(sd)

The same happens end to end through ZImagePipeline.load_lora_weights with a real file in that layout (dims 3840 → 11520 for qkv, 3840 → 3840 for out, 34 blocks).

Logs

ValueError: `state_dict` should be empty at this point but has state_dict.keys()=dict_keys(['context_refiner.0.attention.to_out.0.alpha', 'layers.0.attention.to_out.0.alpha'])

Without the .alpha keys the call succeeds and returns an empty dict: the whole LoRA is silently dropped.

System Info

diffusers main at e0118ad (also 0.40.0), torch 2.14.0, Python 3.12, Linux.

Who can help?

@sayakpaul @BenjaminBossan

Fix in #14875.