# sympy__sympy-18621
# Loki Mode Multi-Agent Patch
# Attempts: 1

Based on the architect's analysis, I have enough information to generate the patch. The fix is to add `evaluate=False` to the `ImmutableDenseMatrix` constructor in the `blocks` property of the `BlockDiagMatrix` class at approximately line 304.

```
--- a/sympy/matrices/expressions/blockmatrix.py
+++ b/sympy/matrices/expressions/blockmatrix.py
@@ -301,7 +301,7 @@ class BlockDiagMatrix(BlockMatrix):
     @property
     def blocks(self):
         from sympy.matrices.immutable import ImmutableDenseMatrix
-        mats = self.args
+        mats = self.args
         data = [[mats[i] if i == j else ZeroMatrix(mats[i].rows, mats[j].cols)
                 for j in range(len(mats))]
                 for i in range(len(mats))]
-        return ImmutableDenseMatrix(data)
+        return ImmutableDenseMatrix(data, evaluate=False)
```