- Step cache 'Off' is preserved: the frontend defaulted to 'off' and mapped it
to an omitted transformer_cache, which the backend now reads as 'auto', so
leaving the control at Off silently enabled FBCache on 20+ step families.
Default the control to Auto, add an explicit Auto option, and send
auto -> omitted so Off maps to an explicit cache-off.
- Kernel auto-install adds --no-deps: 'pip install --only-binary :all: xformers'
resolves xformers' pinned torch and replaces the running torch/triton. --no-deps
installs only the best-effort kernel wheel; an ABI mismatch just fails to import
and falls back to native, never clobbering core deps.
- Do not retry a failed kernel install under the load lock: the pre-install runs
outside the locks, then the in-lock resolve re-attempts pip (up to 600s) while
holding _generate_lock/_lock and blocking unload/cancel/new loads. Record the
attempt in a process-level set so the in-lock call short-circuits to native.
- Cache auto-toggle keys on effective denoise steps: an image-conditioned run with
strength < 1 (upscale default 0.35) denoises a fraction of the requested steps,
so a 28-step request runs ~10 steps. Compute the effective count the way diffusers
get_timesteps does and gate FBCache on it, only when strength is actually applied.
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