docs(upgrading): document RecursiveQuery schema field in upgrade guide

docs/source/library-user-guide/upgrading/55.0.0.md

@@ -894,6 +894,41 @@ let plan = deserialize_bytes(&proto_bytes)?;
 
 See [PR #23827](https://github.com/apache/datafusion/pull/23827) for details.
 
+### `RecursiveQuery` gained a `schema` field
+
+`datafusion_expr::logical_plan::RecursiveQuery` exposed the static (anchor) term's
+schema to parent plans, which ignored columns that only the recursive term makes
+nullable. The node now stores the schema reconciled from both terms explicitly, so
+it can no longer be built with an exhaustive struct literal.
+
+**Who is affected:**
+
+- Code constructing `RecursiveQuery` with a struct literal. This change also
+  shipped in `54.1.0`, so the same migration applies within the `54` series.
+
+**Migration guide:**
+
+Build the node with `RecursiveQuery::try_new`, which computes the schema and
+returns an error if the two terms do not have the same number of columns:
+
+```rust,ignore
+// Before
+let query = RecursiveQuery {
+    name,
+    static_term,
+    recursive_term,
+    is_distinct,
+};
+
+// After
+let query = RecursiveQuery::try_new(name, static_term, recursive_term, is_distinct)?;
+```
+
+`RecursiveQueryExec::try_new` takes the reconciled schema as its second argument
+for the same reason, rather than deriving it from its children.
+
+See [PR #22552](https://github.com/apache/datafusion/pull/22552) for details.
+
 ### `MSRV` updated to 1.94.0
 
 The Minimum Supported Rust Version (MSRV) has been updated to [`1.94.0`].