Concept intervention analysis (5-fold aggregate). Left: Accuracy degradation under increasing Gaussian noise (σ) for HardCBM. Right: Per-concept accuracy recovery at σ = 1.0 when each concept is individually corrected. R₃₁ yields the largest single-concept recovery (+7.3 pp), followed by period (+2.9 pp) and period_snr (+2.6 pp). This per-concept sensitivity ranking is the primary finding of the intervention experiment.