_select_best_seed called value_fn.forward()/compress() directly on a
candidate's captured prediction with no device handling -- the value
function loads CPU-only (map_location='cpu'), but the candidate tensor
lives on whatever device the model ran on (cuda in production). Every
candidate failed to score on every real GPU generation since this
feature shipped; _select_best_seed always fell back to the unchanged
seed, silently a no-op the entire time despite passing all tests
(the suite is CPU-only, so a mismatch never had two devices to hit).
Every other value_function.py call site (gradient/ascend/search) moves
its input onto next(self.parameters()).device first -- this was the
one path that skipped that. Mirrored it: compress on the candidate's
own device (cheap reduction), then move the small compressed vector
onto the value function's device before scoring.
Added a regression test using a real second torch device (mps on this
box, cuda in CI/production) to reproduce the exact cross-device
failure, and fixed three pre-existing value_fn test doubles that were
missing parameters() and had silently started hitting this same
crash branch once the fix started calling it.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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>
