`total_return` from financials.rs:80-94 is log-space cumulative growth
across every per-bar step_return. With ~4M step_returns in a fold-
convergence run, even sub-bps positive bars compound to absurd
magnitudes (observed: 1.93e37%) when displayed as `{:+.2}%`. Math is
correct; display needs scientific notation.
Surfaced in T10 train-multi-seed-xkjkb seed-0 ep3 epoch summary while
SP10 chain validates structural fixes. Cosmetic-only change; no
training-path impact. Audit doc updated with Cosmetic 38.1 entry.
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