fix: rebind a typed node (#25)

This PR allows `Rebind` to work on `schema.TypedNode`. This was a hidden
error because oftentimes the representation form is compatible with the
typed form. However when you start to use custom representations e.g.
tuple, then `Rebind` will not work, since the `datamodel.Node` will have
a map, when represented type expects a list.

The solution is to simply convert a `TypedNode` to it's representation
form prior to binding to the type.

This is likely not used very often - if you have a _typed_ node then you
have/had it in it's native Go type at some point, so you shouldn't need
to rebind. This is however seen it tests, when a server is invoked by a
client without serializing/deserializing capability caveats - and the
validator has to parse already parsed caveats.

core/ipld/rebind.go

@@ -22,6 +22,10 @@ func Rebind[T any](nd datamodel.Node, typ schema.Type) (ptrVal T, err error) {
 		}
 	}()
 
+	if typedNode, ok := nd.(schema.TypedNode); ok {
+		nd = typedNode.Representation()
+	}
+
 	var nilbind T
 	np := bindnode.Prototype(&nilbind, typ)
 	nb := np.Representation().NewBuilder()

core/ipld/rebind_test.go

@@ -8,7 +8,9 @@ import (
 	"github.com/ipld/go-ipld-prime"
 	"github.com/ipld/go-ipld-prime/datamodel"
 	cidlink "github.com/ipld/go-ipld-prime/linking/cid"
+	"github.com/ipld/go-ipld-prime/node/bindnode"
 	"github.com/storacha/go-ucanto/core/ipld/codec/cbor"
+	"github.com/stretchr/testify/require"
 )
 
 func TestRebind(t *testing.T) {
@@ -229,3 +231,27 @@ func TestRebindNonCompatibleSchema(t *testing.T) {
 	}
 	fmt.Println(err)
 }
+
+func TestRebindTypedNode(t *testing.T) {
+	type Target struct {
+		Astring string
+		Aint    int
+	}
+
+	ts, err := ipld.LoadSchemaBytes([]byte(`
+		type Target struct {
+			astring String
+			aint Int
+		} representation tuple
+	`))
+	require.NoError(t, err)
+
+	typ := ts.TypeByName("Target")
+
+	target := Target{Astring: "hello", Aint: 1}
+	nd := bindnode.Wrap(&target, typ)
+
+	rebindTarget, err := Rebind[Target](nd, typ)
+	require.NoError(t, err)
+	fmt.Printf("%+v\n", rebindTarget)
+}