feat: add HTTP migration bridges and extensible API binding

contract/bind.go

@@ -19,7 +19,7 @@ import (
 // strictly decoded, and limited to 1 MiB unless maxBytes is supplied. Query
 // parameters never overwrite path/body/header values. form means URL query only.
 func (b *Binder) Bind(r *http.Request, params map[string]string, target any, maxBytes ...int64) error {
-	if b == nil || r == nil {
+	if b == nil || r == nil || b.schemaOnly {
 		return apierrors.Internal(errors.New("contract: nil binder or request"))
 	}
 	v := reflect.ValueOf(target)
@@ -65,6 +65,10 @@ func (b *Binder) Bind(r *http.Request, params map[string]string, target any, max
 			return tooLarge()
 		}
 		if err != io.EOF {
+			var maxErr *http.MaxBytesError
+			if errors.As(err, &maxErr) {
+				return tooLarge()
+			}
 			return invalid(errors.New("exactly one JSON value required"))
 		}
 		var ok bool
@@ -126,10 +130,16 @@ func tooLarge() error { return apierrors.New(413, "BODY_TOO_LARGE", "request bod
 
 func fromStrings(n *node, values []string) (any, error) {
 	n = base(n)
+	if n.scalar != nil {
+		if len(values) != 1 {
+			return nil, errors.New("duplicate scalar parameter")
+		}
+		return scalarText(values[0]), nil
+	}
 	if n.typ.Kind() == reflect.Slice {
 		out := make([]any, 0, len(values))
 		for _, s := range values {
-			v, err := parseScalar(s, base(n.elem).typ)
+			v, err := fromStrings(n.elem, []string{s})
 			if err != nil {
 				return nil, err
 			}
@@ -158,6 +168,17 @@ func assignField(f field, dst reflect.Value, value any, present bool) error {
 	return checkField(f, dst)
 }
 func setValue(n *node, dst reflect.Value, value any) error {
+	if n.scalar != nil {
+		return n.scalar.decode(dst, value)
+	}
+	if n.typ.Kind() == reflect.Interface && n.typ.NumMethod() == 0 {
+		if value == nil {
+			dst.SetZero()
+		} else {
+			dst.Set(reflect.ValueOf(value))
+		}
+		return nil
+	}
 	if value == nil {
 		if n.typ.Kind() == reflect.Pointer {
 			dst.SetZero()