Attention W_O was Xavier-initialized, injecting ~sqrt(D) magnitude noise
into the residual connection. With the DtoD→copy_f32 fix making attention
active (was a no-op before), random W_O corrupted all branch head inputs
→ MaxDD=100% on validation.
Fix: W_O zero-init → attention starts as identity (output ≈ h_s2).
W_Q/K/V stay Xavier (they project to SDP space, not the residual).
OFI embed weights also zero-init → Mamba2 history starts as [h_s2; 0]
and attention input starts as [h_s2; 0]. No noise injection at init.
Both learn from zero as gradients shape them toward useful patterns.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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