feat(openapi): declare json schema dialect

Co-Authored-By: Virgil <virgil@lethean.io>

openapi.go

@@ -46,6 +46,8 @@ type preparedRouteGroup struct {
 	descs []RouteDescription
 }
 
+const openAPIDialect = "https://spec.openapis.org/oas/3.1/dialect/base"
+
 // Build generates the complete OpenAPI 3.1 JSON spec.
 // Groups implementing DescribableGroup contribute endpoint documentation.
 // Other groups are listed as tags only.
@@ -57,7 +59,8 @@ func (sb *SpecBuilder) Build(groups []RouteGroup) ([]byte, error) {
 	prepared := prepareRouteGroups(groups)
 
 	spec := map[string]any{
-		"openapi": "3.1.0",
+		"openapi":           "3.1.0",
+		"jsonSchemaDialect": openAPIDialect,
 		"info": map[string]any{
 			"title":       sb.Title,
 			"description": sb.Description,

openapi_test.go

@@ -113,6 +113,9 @@ func TestSpecBuilder_Good_EmptyGroups(t *testing.T) {
 	if spec["openapi"] != "3.1.0" {
 		t.Fatalf("expected openapi=3.1.0, got %v", spec["openapi"])
 	}
+	if spec["jsonSchemaDialect"] != "https://spec.openapis.org/oas/3.1/dialect/base" {
+		t.Fatalf("expected jsonSchemaDialect to use the OpenAPI 3.1 base dialect, got %v", spec["jsonSchemaDialect"])
+	}
 
 	// Verify /health path exists.
 	paths := spec["paths"].(map[string]any)