The preload's key-based fxcache lookup failed because the cache key
hash depends on file metadata (size+mtime) which differs between
the precompute pod and hyperopt pod (different PVC mount paths).
Fix: load the first .fxcache file from the cache directory directly.
The precompute step generates exactly one fxcache per dataset — no
ambiguity. Eliminates 285s DBN fallback loading.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>