Tries N candidate seeds with one throwaway denoising step each, scores
each with the trained output-space value function, commits to the
best-scoring seed for the real full pass. Candidates are scored fully
isolated from the scene's own guidance stack (model_function_wrapper
chain, context_windows, v2a_grad_scale, identity_overlap -- each torn
down and reinstalled around the candidate-scoring window) against the
scene's fully-finalized conditioning. Any failure in the value
function, schedule, or the isolation cycle itself degrades to a
silent no-op, declared in the run report, never a crash.
Also hardens _install_context_windows/_install_v2a_scale to roll back
partial state on failure (a leaked context_handler key was silently
re-enabling windowing for later scenes) and fixes the original
non-explore v2a install call site to degrade like its sibling
mechanisms instead of aborting the render.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
