Fix dart-dio webhook imports generating Map-style strings (issue #22586)

Webhook operations were generating broken import statements with Map-style
representation and HTML entity encoding:
  import '{import=model.Pet, classname=Pet}';

Instead of proper Dart package imports:
  import 'package:my-package/src/model/pet.dart';

This occurred because DartDioClientCodegen.postProcessOperationsWithModels()
applied import processing to regular operations, but postProcessWebhooksWithModels()
was missing the same logic.

Fix:
- Extracted shared import processing logic into processImports() method
- Added postProcessWebhooksWithModels() override to apply same logic
- Both operations and webhooks now use consistent import generation

Test:
- Added verifyWebhookImports() test using existing webhooks.yaml resource
- Verifies generated code does not contain Map-style imports
- Verifies generated code does not contain HTML entity encoding

Author: Lutra-Fs

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/DartDioClientCodegen.java

@@ -36,6 +36,7 @@
 import org.openapitools.codegen.model.ModelsMap;
 import org.openapitools.codegen.model.OperationMap;
 import org.openapitools.codegen.model.OperationsMap;
+import org.openapitools.codegen.model.WebhooksMap;
 import org.openapitools.codegen.templating.CommonTemplateContentLocator;
 import org.openapitools.codegen.templating.GeneratorTemplateContentLocator;
 import org.openapitools.codegen.templating.MustacheEngineAdapter;
@@ -649,8 +650,25 @@ public void postProcessModelProperty(CodegenModel model, CodegenProperty propert
     public OperationsMap postProcessOperationsWithModels(OperationsMap objs, List<ModelMap> allModels) {
         super.postProcessOperationsWithModels(objs, allModels);
         OperationMap operations = objs.getOperations();
-        List<CodegenOperation> operationList = operations.getOperation();
+        processImports(operations, operations.getOperation());
+        return objs;
+    }
+
+    @Override
+    public WebhooksMap postProcessWebhooksWithModels(WebhooksMap objs, List<ModelMap> allModels) {
+        super.postProcessWebhooksWithModels(objs, allModels);
+        OperationMap operations = objs.getWebhooks();
+        processImports(operations, operations.getOperation());
+        return objs;
+    }
 
+    /**
+     * Processes imports for operations or webhooks, applying the same logic to both.
+     *
+     * @param operations the OperationMap containing the operations
+     * @param operationList the list of CodegenOperation to process
+     */
+    private void processImports(OperationMap operations, List<CodegenOperation> operationList) {
         Set<String> resultImports = new HashSet<>();
 
         for (CodegenOperation op : operationList) {
@@ -687,7 +705,7 @@ public OperationsMap postProcessOperationsWithModels(OperationsMap objs, List<Mo
             if (SERIALIZATION_LIBRARY_JSON_SERIALIZABLE.equals(library)) {
                 // built_value serialization uses Uint8List for all MultipartFile types
                 // in json_serialization, MultipartFile is used as the file parameter type, but
-                // MultipartFile isn't readable, instead we convert this to a Uin8List
+                // MultipartFile isn't readable, instead we convert this to a Uint8List
                 if (op.isResponseFile) {
                     op.imports.add("Uint8List");
                     op.returnType = "Uint8List";
@@ -729,9 +747,7 @@ public OperationsMap postProcessOperationsWithModels(OperationsMap objs, List<Mo
             }
         }
         // for some reason "import" structure is changed ..
-        objs.put("imports", resultImports.stream().sorted().collect(Collectors.toList()));
-
-        return objs;
+        operations.put("imports", resultImports.stream().sorted().collect(Collectors.toList()));
     }
 
     private void addBuiltValueSerializerImport(String type) {

modules/openapi-generator/src/test/java/org/openapitools/codegen/dart/dio/DartDioClientCodegenTest.java

@@ -115,4 +115,41 @@ public void verifyDartDioGeneratorRuns() throws IOException {
         TestUtils.ensureContainsFile(files, output, "README.md");
         TestUtils.ensureContainsFile(files, output, "lib/src/api.dart");
     }
+
+    @Test
+    public void verifyWebhookImports() throws IOException {
+        File output = Files.createTempDirectory("test").toFile();
+        output.deleteOnExit();
+
+        final CodegenConfigurator configurator = new CodegenConfigurator()
+                .setGeneratorName("dart-dio")
+                .setGitUserId("my-user")
+                .setGitRepoId("my-repo")
+                .setPackageName("my-package")
+                .setInputSpec("src/test/resources/3_1/webhooks.yaml")
+                .setOutputDir(output.getAbsolutePath().replace("\\", "/"));
+
+        ClientOptInput opts = configurator.toClientOptInput();
+
+        Generator generator = new DefaultGenerator().opts(opts);
+        List<File> files = generator.generate();
+        files.forEach(File::deleteOnExit);
+
+        // Find webhook API file (default_api.dart for 'newPet' webhook)
+        File apiDir = new File(output, "lib/src/api");
+        Assert.assertTrue(apiDir.exists() && apiDir.isDirectory(), "API directory should exist");
+
+        File apiFile = new File(apiDir, "default_api.dart");
+        Assert.assertTrue(apiFile.exists(), "default_api.dart should be generated for webhook");
+
+        String apiContent = Files.readString(apiFile.toPath(), StandardCharsets.UTF_8);
+
+        // Bug symptom #22586: Map-style import with HTML entity encoding
+        // Before fix: import '{import&#x3D;model.Pet, classname&#x3D;Pet}';
+        // After fix: import 'package:my_package/lib/src/gen/model/pet.dart';
+        Assert.assertFalse(apiContent.contains("import '{"),
+            "Webhook should not contain Map-style import (bug #22586 symptom)");
+        Assert.assertFalse(apiContent.contains("&#x3D;"),
+            "Webhook should not contain HTML entity encoding (bug #22586 symptom)");
+    }
 }