Fix MHC_DIAG null check when SKIP_MHC is enabled

single_shot_inference.py

@@ -406,7 +406,7 @@ def forward_layer(X_l, w, li, cfg, rope_cos, rope_sin,
     else:
         # -- mHC pre_block (attention) --
         x_in, attn_ctx = attn_mhc.pre_block(X_l)  # x_in: (T, H)
-    if MHC_DIAG:  # mHC diagnostics
+    if MHC_DIAG and attn_ctx is not None:  # mHC diagnostics
         B_l, C_l = attn_ctx.B_l, attn_ctx.C_l
         print(f"  L{li} pre_attn: |X_l|={X_l.abs().max().item():.2f} |x_in|={x_in.abs().max().item():.2f}", flush=True)
 
@@ -558,7 +558,7 @@ def forward_layer(X_l, w, li, cfg, rope_cos, rope_sin,
         # -- mHC post_block (attention) --
         X_mid = attn_mhc.post_block(X_l, F_attn, attn_ctx)  # (T, n_hc, H)
     # Diagnostic: check mHC is stabilizing the residual
-    if MHC_DIAG:  # mHC diagnostics
+    if MHC_DIAG and attn_ctx is not None:  # mHC diagnostics
         B_l, C_l = attn_ctx.B_l, attn_ctx.C_l
         print(f"  L{li} attn: |X_l|={X_l.abs().max().item():.2f} |F_attn|={F_attn.abs().max().item():.2f} |B|={B_l.abs().max().item():.4f} |C|={C_l.abs().max().item():.4f} |X_mid|={X_mid.abs().max().item():.2f}")
         # Check B_l is doubly stochastic (rows sum to 1.0)
@@ -589,7 +589,7 @@ def forward_layer(X_l, w, li, cfg, rope_cos, rope_sin,
     else:
         # -- mHC post_block (FFN) --
         X_next = ffn_mhc.post_block(X_mid, F_ffn, ffn_ctx)  # (T, n_hc, H)
-    if MHC_DIAG:  # ffn mHC diagnostics
+    if MHC_DIAG and ffn_ctx is not None:  # ffn mHC diagnostics
         B_l_ffn, C_l_ffn = ffn_ctx.B_l, ffn_ctx.C_l
         print(f"  L{li} ffn: |X_mid|={X_mid.abs().max().item():.2f} |F_ffn|={F_ffn.abs().max().item():.2f} |B|={B_l_ffn.abs().max().item():.4f} |C|={C_l_ffn.abs().max().item():.4f} |X_next|={X_next.abs().max().item():.2f}", flush=True)