feat(validation): add machine-readable Code and Params to ErrorDetail

error.go

@@ -28,6 +28,17 @@ type ErrorDetail struct {
 	// the client didn't send extra whitespace or help when the client
 	// did not log an outgoing request.
 	Value any `json:"value,omitempty" doc:"The value at the given location"`
+
+	// Code is a machine-readable identifier for the error type, corresponding
+	// to one of the validation.Code* constants. It enables programmatic error
+	// handling without parsing the human-readable Message field.
+	Code string `json:"code,omitempty" doc:"Machine-readable error code"`
+
+	// Params contains the constraint parameters relevant to the error, e.g.
+	// {"allowed": ["a","b"]} for a CodeExpectedOneOf error or {"min": 3} for
+	// a CodeExpectedMinLength error. It is omitted when there are no relevant
+	// parameters.
+	Params map[string]any `json:"params,omitempty" doc:"Constraint parameters for the error"`
 }
 
 // Error returns the error message / satisfies the `error` interface. If a

huma_test.go

@@ -3333,15 +3333,21 @@ func TestExhaustiveErrors(t *testing.T) {
 			{
 				"message": "expected number <= 10",
 				"location": "path.id",
-				"value": 15
+				"value": 15,
+				"code": "expected_maximum_number",
+				"params": {"max": 10}
 			}, {
 				"message": "expected number >= 1",
 				"location": "body.count",
-				"value": -6
+				"value": -6,
+				"code": "expected_minimum_number",
+				"params": {"min": 1}
 			}, {
 				"message": "expected length <= 10",
 				"location": "body.name",
-				"value": "12345678901"
+				"value": "12345678901",
+				"code": "expected_max_length",
+				"params": {"max": 10}
 			}, {
 				"message": "input resolver error",
 				"location": "path.id",