Two truncation sites in data_loading.rs truncated feature/target vectors
to max_bars but left self.ofi_features at the original (cache-full)
length. Downstream DqnGpuData::upload_slices asserts OFI len == num_bars
and surfaced this as "OFI/market data length mismatch: 175874 OFI rows
vs 5000 bars — fxcache is corrupt".
The cache was not corrupt — the upstream truncation was the bug. Fixed
by moving OFI storage below the truncation block in the fxcache path and
by adding a parallel truncate in the DBN fallback path. Added
debug_assert_eq on equal lengths post-truncation so future regressions
hard-fail in dev.
Also corrected the cuda_pipeline/mod.rs error message to point at the
actual culprit (upstream truncation desync) instead of blaming the
on-disk cache.
2ac956298b