Re-reviewed each merged phase PR against this branch's tip and fixed what is
still real:
- A superseded background load no longer cancels the current model's in-flight
generation: the load-token check now runs BEFORE the cancel signal, with a
re-check under the generate lock (Phase 1 review).
- enable_model_cpu_offload / enable_sequential_cpu_offload now forward the
resolved target device; diffusers defaults to CUDA, which broke offloaded
loads on non-CUDA accelerators such as Intel XPU (Phase 2 review).
- build_sd_cpp_command rejects a None prompt (str(None) previously slipped
into argv as the literal "None") and a mask without an init image, which
is an invalid sd-cli inpaint invocation (Phase 4/6 review).
- The dense-quant OOM fallback drops the caught exception before
clear_gpu_cache(): the traceback pinned the partially built dense
transformer, so the VRAM this cleanup exists to reclaim stayed allocated
through the GGUF rebuild (Phase 8 review).
- Pre-quantized transformers (built via from_config) are eval()'d to match
the from_pretrained paths, so train-mode layers cannot make prequant
inference nondeterministic (Phase 9 review).
- FBCache state is reset before each generation when a step cache is engaged:
diffusers never clears the stateful first-block residuals on the resident
transformer, so a resolution or batch change on the next request hit a
shape mismatch, and an unchanged request could reuse stale residuals
(Phase 12 review).
Each fix carries a regression test; the full diffusion battery passes.
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