Document that erase may invalidate search path

It doesn't yet, but it will when we downsize nodes.

ConflictSet.cpp

@@ -727,7 +727,8 @@ Node *nextLogical(Node *node) {
   return node;
 }
 
-// Precondition: self is not the root
+// Precondition: self is not the root. May invalidate nodes along the search
+// path to self.
 Node *erase(Node *self, NodeAllocators *allocators, ConflictSet::Impl *impl) {
   assert(self->parent != nullptr);
 
@@ -1577,7 +1578,7 @@ bool checkRangeRead(Node *n, std::span<const uint8_t> begin,
 // Returns a pointer to the newly inserted node.  Caller must set
 // `entryPresent`, `entry` fields and `maxVersion` on the result.  The search
 // path of the result's parent will have `maxVersion` at least `writeVersion` as
-// a postcondition. Nodes along the search path may be invalidated.
+// a postcondition. Nodes along the search path to `key` may be invalidated.
 template <bool kBegin>
 [[nodiscard]] Node *insert(Node **self, std::span<const uint8_t> key,
                            int64_t writeVersion, NodeAllocators *allocators,