Make QKV hook robust against shape mismatches

- Add try-except around entire hook body
- Validate tensor dimensions before reshape
- Skip QKV capture silently if format doesn't match
- Prevents crashes during forward pass with different model architectures

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

backend/model_service.py

@@ -1314,17 +1314,26 @@ async def analyze_research_attention(request: Dict[str, Any], authenticated: boo
 
         def make_qkv_hook(layer_idx):
             def hook(module, input, output):
-                # output shape: [batch, seq_len, 3 * hidden_size]
-                # Split into Q, K, V
-                batch_size, seq_len, _ = output.shape
-                qkv = output.reshape(batch_size, seq_len, 3, n_heads, head_dim)
-                # Separate Q, K, V: [batch, seq_len, n_heads, head_dim]
-                q, k, v = qkv[:, :, 0], qkv[:, :, 1], qkv[:, :, 2]
-                qkv_captures[layer_idx] = {
-                    'q': q[0].detach().cpu(),  # Remove batch dim
-                    'k': k[0].detach().cpu(),
-                    'v': v[0].detach().cpu()
-                }
+                try:
+                    # output shape: [batch, seq_len, 3 * hidden_size]
+                    # Split into Q, K, V
+                    if output.dim() != 3:
+                        return  # Skip if unexpected shape
+                    batch_size, seq_len, hidden = output.shape
+                    expected_hidden = 3 * n_heads * head_dim
+                    if hidden != expected_hidden:
+                        return  # Skip if dimensions don't match QKV format
+                    qkv = output.reshape(batch_size, seq_len, 3, n_heads, head_dim)
+                    # Separate Q, K, V: [batch, seq_len, n_heads, head_dim]
+                    q, k, v = qkv[:, :, 0], qkv[:, :, 1], qkv[:, :, 2]
+                    qkv_captures[layer_idx] = {
+                        'q': q[0].detach().cpu(),  # Remove batch dim
+                        'k': k[0].detach().cpu(),
+                        'v': v[0].detach().cpu()
+                    }
+                except Exception:
+                    # Silently skip QKV capture if it fails - it's optional data
+                    pass
             return hook
 
         # Register hooks on all qkv_proj modules (if available)