refactor(miniscript): Remove Node::subs mutability

diff --git a/src/script/descriptor.cpp b/src/script/descriptor.cpp
index 390e7345..8769a262 100644
--- a/src/script/descriptor.cpp
+++ b/src/script/descriptor.cpp
@@ -2566,7 +2566,7 @@ std::vector<std::unique_ptr<DescriptorImpl>> ParseScript(uint32_t& key_exp_index
             }
             if (!node->IsSane() || node->IsNotSatisfiable()) {
                 // Try to find the first insane sub for better error reporting.
-                auto insane_node = node.get();
+                const decltype(node)::element_type* insane_node = node.get();
                 if (const auto sub = node->FindInsaneSub()) insane_node = sub;
                 error = *insane_node->ToString(parser);
                 if (!insane_node->IsValid()) {
diff --git a/src/script/miniscript.h b/src/script/miniscript.h
index 1c5f7a8c..92925396 100644
--- a/src/script/miniscript.h
+++ b/src/script/miniscript.h
@@ -191,11 +191,11 @@ inline consteval Type operator""_mst(const char* c, size_t l)
 using Opcode = std::pair<opcodetype, std::vector<unsigned char>>;
 
 template<typename Key> class Node;
-template<typename Key> using NodeRef = std::unique_ptr<const Node<Key>>;
+template<typename Key> using NodeRef = std::unique_ptr<Node<Key>>;
 
 //! Construct a miniscript node as a unique_ptr.
 template<typename Key, typename... Args>
-NodeRef<Key> MakeNodeRef(Args&&... args) { return std::make_unique<const Node<Key>>(std::forward<Args>(args)...); }
+NodeRef<Key> MakeNodeRef(Args&&... args) { return std::make_unique<Node<Key>>(std::forward<Args>(args)...); }
 
 //! Unordered traversal of a miniscript node tree.
 template <typename Key, std::invocable<const Node<Key>&> Fn>
@@ -545,7 +545,7 @@ class Node
     //! The data bytes in this expression (only for HASH160/HASH256/SHA256/RIPEMD160).
     std::vector<unsigned char> data;
     //! Subexpressions (for WRAP_*/AND_*/OR_*/ANDOR/THRESH)
-    mutable std::vector<NodeRef<Key>> subs;
+    std::vector<NodeRef<Key>> subs;
     //! The Script context for this node. Either P2WSH or Tapscript.
     MiniscriptContext m_script_ctx;