feat(openapi): mark deprecated operations in spec

Expose route-level deprecation in generated OpenAPI operations and cover it with a regression test.

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

docs/architecture.md

@@ -128,6 +128,7 @@ type RouteDescription struct {
     Summary     string
     Description string
     Tags        []string
+    Deprecated  bool
     StatusCode  int
     Parameters  []ParameterDescription
     RequestBody map[string]any

group.go

@@ -39,6 +39,8 @@ type RouteDescription struct {
 	Summary     string   // Short summary
 	Description string   // Long description
 	Tags        []string // OpenAPI tags for grouping
+	// Deprecated marks the operation as deprecated in OpenAPI.
+	Deprecated bool
 	// StatusCode is the documented 2xx success status code.
 	// Zero defaults to 200.
 	StatusCode int

openapi.go

@@ -166,6 +166,9 @@ func (sb *SpecBuilder) buildPaths(groups []RouteGroup) map[string]any {
 				"operationId": operationID(method, fullPath, operationIDs),
 				"responses":   operationResponses(method, rd.StatusCode, rd.Response),
 			}
+			if rd.Deprecated {
+				operation["deprecated"] = true
+			}
 			if rd.Security != nil {
 				operation["security"] = rd.Security
 			} else {

openapi_test.go

@@ -1129,6 +1129,48 @@ func TestSpecBuilder_Good_DefaultTagsFromGroupName(t *testing.T) {
 	}
 }
 
+func TestSpecBuilder_Good_DeprecatedOperation(t *testing.T) {
+	sb := &api.SpecBuilder{
+		Title:   "Test",
+		Version: "1.0.0",
+	}
+
+	group := &specStubGroup{
+		name:     "legacy",
+		basePath: "/api/legacy",
+		descs: []api.RouteDescription{
+			{
+				Method:     "GET",
+				Path:       "/status",
+				Summary:    "Check legacy status",
+				Deprecated: true,
+				Response: map[string]any{
+					"type": "object",
+				},
+			},
+		},
+	}
+
+	data, err := sb.Build([]api.RouteGroup{group})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	var spec map[string]any
+	if err := json.Unmarshal(data, &spec); err != nil {
+		t.Fatalf("invalid JSON: %v", err)
+	}
+
+	op := spec["paths"].(map[string]any)["/api/legacy/status"].(map[string]any)["get"].(map[string]any)
+	deprecated, ok := op["deprecated"].(bool)
+	if !ok {
+		t.Fatalf("expected deprecated boolean, got %T", op["deprecated"])
+	}
+	if !deprecated {
+		t.Fatal("expected deprecated operation to be marked true")
+	}
+}
+
 func TestSpecBuilder_Good_BlankTagsAreIgnored(t *testing.T) {
 	sb := &api.SpecBuilder{
 		Title:   "Test",