diff --git a/modules/openapi-generator/src/main/resources/dart/libraries/dio/api.mustache b/modules/openapi-generator/src/main/resources/dart/libraries/dio/api.mustache
index ac0e989c6141..1914de69254d 100644
--- a/modules/openapi-generator/src/main/resources/dart/libraries/dio/api.mustache
+++ b/modules/openapi-generator/src/main/resources/dart/libraries/dio/api.mustache
@@ -51,7 +51,7 @@ class {{classname}} {
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'{{{path}}}'{{#pathParams}}.replaceAll('{' r'{{{baseName}}}' '}', {{#includeLibraryTemplate}}api/query_param{{/includeLibraryTemplate}}.toString()){{/pathParams}};
+    final _path = r'{{{path}}}'{{#pathParams}}.replaceAll('{' r'{{{baseName}}}' '}', {{#includeLibraryTemplate}}api/path_param{{/includeLibraryTemplate}},){{/pathParams}};
     final _options = Options(
       method: r'{{#lambda.uppercase}}{{httpMethod}}{{/lambda.uppercase}}',
       {{#isResponseFile}}
diff --git a/modules/openapi-generator/src/main/resources/dart/libraries/dio/pubspec.mustache b/modules/openapi-generator/src/main/resources/dart/libraries/dio/pubspec.mustache
index 1d7352f8cc26..40a3771c4fec 100644
--- a/modules/openapi-generator/src/main/resources/dart/libraries/dio/pubspec.mustache
+++ b/modules/openapi-generator/src/main/resources/dart/libraries/dio/pubspec.mustache
@@ -54,5 +54,12 @@ dev_dependencies:
   build_runner: any
   freezed: '^3.0.0'
   json_serializable: '^6.9.3'
+  # unlike the json_serializable variant, this one has no copy_with_extension_gen
+  # whose source_gen constraint would hold source_helper back; source_helper 1.4.0
+  # added extension members that clash with json_serializable 6.x's internal
+  # copies and break the build_runner build script, so hold it below 1.4.0.
+  # 1.3.9+ requires Dart 3.9 while this variant advertises >=3.8.0, so keep the
+  # 1.3.8 lower bound resolvable for 3.8 users
+  source_helper: '>=1.3.8 <1.4.0'
 {{/useFreezed}}
   test: '^1.16.0'
diff --git a/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/api/path_param.mustache b/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/api/path_param.mustache
new file mode 100644
index 000000000000..1d633242d7cd
--- /dev/null
+++ b/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/api/path_param.mustache
@@ -0,0 +1 @@
+Uri.encodeComponent({{#includeLibraryTemplate}}api/query_param{{/includeLibraryTemplate}}.toString())
\ No newline at end of file
diff --git a/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/freezed/api/path_param.mustache b/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/freezed/api/path_param.mustache
new file mode 100644
index 000000000000..1d633242d7cd
--- /dev/null
+++ b/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/freezed/api/path_param.mustache
@@ -0,0 +1 @@
+Uri.encodeComponent({{#includeLibraryTemplate}}api/query_param{{/includeLibraryTemplate}}.toString())
\ No newline at end of file
diff --git a/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/json_serializable/api/path_param.mustache b/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/json_serializable/api/path_param.mustache
new file mode 100644
index 000000000000..1d633242d7cd
--- /dev/null
+++ b/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/json_serializable/api/path_param.mustache
@@ -0,0 +1 @@
+Uri.encodeComponent({{#includeLibraryTemplate}}api/query_param{{/includeLibraryTemplate}}.toString())
\ No newline at end of file
diff --git a/modules/openapi-generator/src/main/resources/ruby-nextgen/gem.mustache b/modules/openapi-generator/src/main/resources/ruby-nextgen/gem.mustache
index e411a4277681..68ee988370d9 100644
--- a/modules/openapi-generator/src/main/resources/ruby-nextgen/gem.mustache
+++ b/modules/openapi-generator/src/main/resources/ruby-nextgen/gem.mustache
@@ -21,10 +21,9 @@ module {{moduleName}}
     attr_reader :loader
   end
 
-{{#moduleNameNested}}
-  # Nested moduleName: for_gem can't target a nested namespace, so drive Zeitwerk
-  # explicitly. The parent module(s) above are pre-defined so `module {{moduleName}}`
-  # (here and in every generated file) reopens rather than raising NameError.
+  # for_gem derives the namespace from gemName, which need not match moduleName (and
+  # can't target a nested one), so drive Zeitwerk explicitly. Any parent module(s) above
+  # are pre-defined so `module {{moduleName}}` reopens rather than raising NameError.
   @loader = Zeitwerk::Loader.new
   @loader.push_dir("#{__dir__}/{{gemName}}", namespace: self)
   # version.rb defines VERSION (not a `Version` class). for_gem's GemInflector special-cases
@@ -32,10 +31,6 @@ module {{moduleName}}
   # {{moduleName}}::VERSION available.
   @loader.ignore("#{__dir__}/{{gemName}}/version.rb")
   require_relative "{{gemName}}/version"
-{{/moduleNameNested}}
-{{^moduleNameNested}}
-  @loader = Zeitwerk::Loader.for_gem
-{{/moduleNameNested}}
 {{#zeitwerkInflections.0}}
   # Model names keep their acronym casing (e.g. HTTPConfig), but Zeitwerk's default
   # inflector would expect HttpConfig from the file name. Register the exceptions so
diff --git a/modules/openapi-generator/src/test/java/org/openapitools/codegen/dart/dio/DartDioClientCodegenTest.java b/modules/openapi-generator/src/test/java/org/openapitools/codegen/dart/dio/DartDioClientCodegenTest.java
index acdf8de1cffc..e501bb1d5c0d 100644
--- a/modules/openapi-generator/src/test/java/org/openapitools/codegen/dart/dio/DartDioClientCodegenTest.java
+++ b/modules/openapi-generator/src/test/java/org/openapitools/codegen/dart/dio/DartDioClientCodegenTest.java
@@ -471,6 +471,47 @@ public void testFreezedIgnoresUseOptional() throws IOException {
         TestUtils.assertFileNotContains(output.toPath().resolve("lib/src/model/pet.dart"), "Optional<");
     }
 
+    /**
+     * Path parameters must be URI-encoded as path components: the query_param helpers pass
+     * strings through unchanged, so a value containing '/' or spaces would otherwise break
+     * the request path. Every path substitution must therefore go through
+     * Uri.encodeComponent.
+     */
+    @Test
+    public void testPathParamsAreUriEncoded() throws IOException {
+        for (Object[] libraryOption : serializationLibraries()) {
+            String serializationLibrary = (String) libraryOption[0];
+            File output = Files.createTempDirectory("test").toFile();
+            output.deleteOnExit();
+
+            final CodegenConfigurator configurator = new CodegenConfigurator()
+                    .setGeneratorName("dart-dio")
+                    .setInputSpec("src/test/resources/3_0/petstore.yaml")
+                    .setOutputDir(output.getAbsolutePath().replace("\\", "/"))
+                    .addAdditionalProperty(CodegenConstants.SERIALIZATION_LIBRARY, serializationLibrary);
+
+            ClientOptInput opts = configurator.toClientOptInput();
+            Generator generator = new DefaultGenerator().opts(opts);
+            List<File> files = generator.generate();
+            files.forEach(File::deleteOnExit);
+
+            // check every generated api class, not just one
+            Path apiDir = output.toPath().resolve("lib/src/api");
+            try (var apiFiles = Files.list(apiDir)) {
+                for (Path apiFile : apiFiles.filter(p -> p.getFileName().toString().endsWith("_api.dart"))
+                        .collect(java.util.stream.Collectors.toList())) {
+                    String content = Files.readString(apiFile, StandardCharsets.UTF_8);
+                    int substitutions = content.split("\\.replaceAll\\(", -1).length - 1;
+                    Assert.assertTrue(substitutions > 0,
+                            "expected path substitutions in " + apiFile + ": " + content);
+                    int encodings = content.split("Uri\\.encodeComponent\\(", -1).length - 1;
+                    Assert.assertEquals(encodings, substitutions,
+                            "every path substitution in " + apiFile + " must be URI-encoded: " + content);
+                }
+            }
+        }
+    }
+
     private Path generateFormParamsClient(String serializationLibrary) throws IOException {
         File output = Files.createTempDirectory("test").toFile();
         output.deleteOnExit();
diff --git a/modules/openapi-generator/src/test/java/org/openapitools/codegen/rubynextgen/RubyNextgenClientCodegenTest.java b/modules/openapi-generator/src/test/java/org/openapitools/codegen/rubynextgen/RubyNextgenClientCodegenTest.java
index 4158d40b4961..d914f9527319 100644
--- a/modules/openapi-generator/src/test/java/org/openapitools/codegen/rubynextgen/RubyNextgenClientCodegenTest.java
+++ b/modules/openapi-generator/src/test/java/org/openapitools/codegen/rubynextgen/RubyNextgenClientCodegenTest.java
@@ -443,6 +443,31 @@ public void testAcronymModelsGetZeitwerkInflections() throws Exception {
                 "@two_fa_whitelist ||= DedicatedCloud::TwoFAWhitelist.new(@connection)");
     }
 
+    @Test
+    public void testZeitwerkLoaderWhenModuleNameDiffersFromGemName() throws Exception {
+        java.nio.file.Path target = java.nio.file.Files.createTempDirectory("test");
+        target.toFile().deleteOnExit();
+        org.openapitools.codegen.ClientOptInput input =
+                new org.openapitools.codegen.config.CodegenConfigurator()
+                        .setGeneratorName("ruby-nextgen")
+                        .setInputSpec("src/test/resources/3_0/ruby-nextgen/acronym.yaml")
+                        .setOutputDir(target.toString())
+                        // camelized gemName would be ThingsApi, but the namespace is Things:
+                        // Zeitwerk::Loader.for_gem would target ThingsApi and autoload nothing
+                        .addAdditionalProperty("gemName", "things_api")
+                        .addAdditionalProperty("moduleName", "Things")
+                        .toClientOptInput();
+        new org.openapitools.codegen.DefaultGenerator(false).opts(input).generate();
+
+        // the explicit loader targets the moduleName namespace regardless of gemName
+        org.openapitools.codegen.TestUtils.assertFileContains(
+                target.resolve("lib/things_api.rb"),
+                "Zeitwerk::Loader.new",
+                "@loader.push_dir(\"#{__dir__}/things_api\", namespace: self)");
+        org.openapitools.codegen.TestUtils.assertFileNotContains(
+                target.resolve("lib/things_api.rb"), "Zeitwerk::Loader.for_gem");
+    }
+
     @Test
     public void testNestedResourcesAreReachableFromClient() throws Exception {
         java.nio.file.Path target = java.nio.file.Files.createTempDirectory("test");
diff --git a/samples/client/others/ruby-nextgen-qdrant/lib/qdrant.rb b/samples/client/others/ruby-nextgen-qdrant/lib/qdrant.rb
index 5be13f72f31e..612cc605f078 100644
--- a/samples/client/others/ruby-nextgen-qdrant/lib/qdrant.rb
+++ b/samples/client/others/ruby-nextgen-qdrant/lib/qdrant.rb
@@ -20,7 +20,16 @@ class << self
     attr_reader :loader
   end
 
-  @loader = Zeitwerk::Loader.for_gem
+  # for_gem derives the namespace from gemName, which need not match moduleName (and
+  # can't target a nested one), so drive Zeitwerk explicitly. Any parent module(s) above
+  # are pre-defined so `module Qdrant` reopens rather than raising NameError.
+  @loader = Zeitwerk::Loader.new
+  @loader.push_dir("#{__dir__}/qdrant", namespace: self)
+  # version.rb defines VERSION (not a `Version` class). for_gem's GemInflector special-cases
+  # this; a plain Loader doesn't, so ignore it for autoloading and require it directly to keep
+  # Qdrant::VERSION available.
+  @loader.ignore("#{__dir__}/qdrant/version.rb")
+  require_relative "qdrant/version"
   # The `api/` directory on disk is fixed regardless of the `apiNamespace` CliOption,
   # but api.mustache only nests classes under an `Api` module when the wrapper is
   # enabled (true). When it's disabled, tell Zeitwerk to collapse
diff --git a/samples/client/petstore/ruby-nextgen/lib/petstore.rb b/samples/client/petstore/ruby-nextgen/lib/petstore.rb
index 19e492b7a84c..8ee009b7e8c1 100644
--- a/samples/client/petstore/ruby-nextgen/lib/petstore.rb
+++ b/samples/client/petstore/ruby-nextgen/lib/petstore.rb
@@ -19,7 +19,16 @@ class << self
     attr_reader :loader
   end
 
-  @loader = Zeitwerk::Loader.for_gem
+  # for_gem derives the namespace from gemName, which need not match moduleName (and
+  # can't target a nested one), so drive Zeitwerk explicitly. Any parent module(s) above
+  # are pre-defined so `module Petstore` reopens rather than raising NameError.
+  @loader = Zeitwerk::Loader.new
+  @loader.push_dir("#{__dir__}/petstore", namespace: self)
+  # version.rb defines VERSION (not a `Version` class). for_gem's GemInflector special-cases
+  # this; a plain Loader doesn't, so ignore it for autoloading and require it directly to keep
+  # Petstore::VERSION available.
+  @loader.ignore("#{__dir__}/petstore/version.rb")
+  require_relative "petstore/version"
   # The `api/` directory on disk is fixed regardless of the `apiNamespace` CliOption,
   # but api.mustache only nests classes under an `Api` module when the wrapper is
   # enabled (true). When it's disabled, tell Zeitwerk to collapse
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore-timemachine/lib/src/api/pet_api.dart b/samples/openapi3/client/petstore/dart-dio/petstore-timemachine/lib/src/api/pet_api.dart
index 8aaf646e3051..6161c2f7eb2d 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore-timemachine/lib/src/api/pet_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio/petstore-timemachine/lib/src/api/pet_api.dart
@@ -146,7 +146,7 @@ class PetApi {
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/pet/{petId}'.replaceAll('{' r'petId' '}', encodeQueryParameter(_serializers, petId, const FullType(int)).toString());
+    final _path = r'/pet/{petId}'.replaceAll('{' r'petId' '}', Uri.encodeComponent(encodeQueryParameter(_serializers, petId, const FullType(int)).toString()),);
     final _options = Options(
       method: r'DELETE',
       headers: <String, dynamic>{
@@ -370,7 +370,7 @@ class PetApi {
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/pet/{petId}'.replaceAll('{' r'petId' '}', encodeQueryParameter(_serializers, petId, const FullType(int)).toString());
+    final _path = r'/pet/{petId}'.replaceAll('{' r'petId' '}', Uri.encodeComponent(encodeQueryParameter(_serializers, petId, const FullType(int)).toString()),);
     final _options = Options(
       method: r'GET',
       headers: <String, dynamic>{
@@ -558,7 +558,7 @@ class PetApi {
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/pet/{petId}'.replaceAll('{' r'petId' '}', encodeQueryParameter(_serializers, petId, const FullType(int)).toString());
+    final _path = r'/pet/{petId}'.replaceAll('{' r'petId' '}', Uri.encodeComponent(encodeQueryParameter(_serializers, petId, const FullType(int)).toString()),);
     final _options = Options(
       method: r'POST',
       headers: <String, dynamic>{
@@ -636,7 +636,7 @@ class PetApi {
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/pet/{petId}/uploadImage'.replaceAll('{' r'petId' '}', encodeQueryParameter(_serializers, petId, const FullType(int)).toString());
+    final _path = r'/pet/{petId}/uploadImage'.replaceAll('{' r'petId' '}', Uri.encodeComponent(encodeQueryParameter(_serializers, petId, const FullType(int)).toString()),);
     final _options = Options(
       method: r'POST',
       headers: <String, dynamic>{
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore-timemachine/lib/src/api/store_api.dart b/samples/openapi3/client/petstore/dart-dio/petstore-timemachine/lib/src/api/store_api.dart
index 5ad35b28d39a..ebd11aef63e3 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore-timemachine/lib/src/api/store_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio/petstore-timemachine/lib/src/api/store_api.dart
@@ -43,7 +43,7 @@ class StoreApi {
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/store/order/{orderId}'.replaceAll('{' r'orderId' '}', encodeQueryParameter(_serializers, orderId, const FullType(String)).toString());
+    final _path = r'/store/order/{orderId}'.replaceAll('{' r'orderId' '}', Uri.encodeComponent(encodeQueryParameter(_serializers, orderId, const FullType(String)).toString()),);
     final _options = Options(
       method: r'DELETE',
       headers: <String, dynamic>{
@@ -170,7 +170,7 @@ class StoreApi {
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/store/order/{orderId}'.replaceAll('{' r'orderId' '}', encodeQueryParameter(_serializers, orderId, const FullType(int)).toString());
+    final _path = r'/store/order/{orderId}'.replaceAll('{' r'orderId' '}', Uri.encodeComponent(encodeQueryParameter(_serializers, orderId, const FullType(int)).toString()),);
     final _options = Options(
       method: r'GET',
       headers: <String, dynamic>{
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore-timemachine/lib/src/api/user_api.dart b/samples/openapi3/client/petstore/dart-dio/petstore-timemachine/lib/src/api/user_api.dart
index c052b91ccf63..7555893e7eb5 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore-timemachine/lib/src/api/user_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio/petstore-timemachine/lib/src/api/user_api.dart
@@ -266,7 +266,7 @@ class UserApi {
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/user/{username}'.replaceAll('{' r'username' '}', encodeQueryParameter(_serializers, username, const FullType(String)).toString());
+    final _path = r'/user/{username}'.replaceAll('{' r'username' '}', Uri.encodeComponent(encodeQueryParameter(_serializers, username, const FullType(String)).toString()),);
     final _options = Options(
       method: r'DELETE',
       headers: <String, dynamic>{
@@ -320,7 +320,7 @@ class UserApi {
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/user/{username}'.replaceAll('{' r'username' '}', encodeQueryParameter(_serializers, username, const FullType(String)).toString());
+    final _path = r'/user/{username}'.replaceAll('{' r'username' '}', Uri.encodeComponent(encodeQueryParameter(_serializers, username, const FullType(String)).toString()),);
     final _options = Options(
       method: r'GET',
       headers: <String, dynamic>{
@@ -529,7 +529,7 @@ class UserApi {
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/user/{username}'.replaceAll('{' r'username' '}', encodeQueryParameter(_serializers, username, const FullType(String)).toString());
+    final _path = r'/user/{username}'.replaceAll('{' r'username' '}', Uri.encodeComponent(encodeQueryParameter(_serializers, username, const FullType(String)).toString()),);
     final _options = Options(
       method: r'PUT',
       headers: <String, dynamic>{
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-freezed/lib/src/api/pet_api.dart b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-freezed/lib/src/api/pet_api.dart
index ada4f50fa6bb..8c6df90231db 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-freezed/lib/src/api/pet_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-freezed/lib/src/api/pet_api.dart
@@ -118,7 +118,7 @@ class PetApi {
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/pet/{petId}'.replaceAll('{' r'petId' '}', petId.toString());
+    final _path = r'/pet/{petId}'.replaceAll('{' r'petId' '}', Uri.encodeComponent(petId.toString()),);
     final _options = Options(
       method: r'DELETE',
       headers: <String, dynamic>{
@@ -336,7 +336,7 @@ _responseData = rawData == null ? null : deserialize<Set<Pet>, Pet>(rawData, 'Se
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/pet/{petId}'.replaceAll('{' r'petId' '}', petId.toString());
+    final _path = r'/pet/{petId}'.replaceAll('{' r'petId' '}', Uri.encodeComponent(petId.toString()),);
     final _options = Options(
       method: r'GET',
       headers: <String, dynamic>{
@@ -494,7 +494,7 @@ _responseData = rawData == null ? null : deserialize<Pet, Pet>(rawData, 'Pet', g
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/pet/{petId}'.replaceAll('{' r'petId' '}', petId.toString());
+    final _path = r'/pet/{petId}'.replaceAll('{' r'petId' '}', Uri.encodeComponent(petId.toString()),);
     final _options = Options(
       method: r'POST',
       headers: <String, dynamic>{
@@ -572,7 +572,7 @@ _responseData = rawData == null ? null : deserialize<Pet, Pet>(rawData, 'Pet', g
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/pet/{petId}/uploadImage'.replaceAll('{' r'petId' '}', petId.toString());
+    final _path = r'/pet/{petId}/uploadImage'.replaceAll('{' r'petId' '}', Uri.encodeComponent(petId.toString()),);
     final _options = Options(
       method: r'POST',
       headers: <String, dynamic>{
@@ -675,7 +675,7 @@ _responseData = rawData == null ? null : deserialize<ApiResponse, ApiResponse>(r
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/fake/{petId}/uploadImageWithRequiredFile'.replaceAll('{' r'petId' '}', petId.toString());
+    final _path = r'/fake/{petId}/uploadImageWithRequiredFile'.replaceAll('{' r'petId' '}', Uri.encodeComponent(petId.toString()),);
     final _options = Options(
       method: r'POST',
       headers: <String, dynamic>{
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-freezed/lib/src/api/store_api.dart b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-freezed/lib/src/api/store_api.dart
index f3d48dc3d1f1..0b9117eeb2f8 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-freezed/lib/src/api/store_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-freezed/lib/src/api/store_api.dart
@@ -40,7 +40,7 @@ class StoreApi {
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/store/order/{order_id}'.replaceAll('{' r'order_id' '}', orderId.toString());
+    final _path = r'/store/order/{order_id}'.replaceAll('{' r'order_id' '}', Uri.encodeComponent(orderId.toString()),);
     final _options = Options(
       method: r'DELETE',
       headers: <String, dynamic>{
@@ -164,7 +164,7 @@ _responseData = rawData == null ? null : deserialize<Map<String, int>, int>(rawD
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/store/order/{order_id}'.replaceAll('{' r'order_id' '}', orderId.toString());
+    final _path = r'/store/order/{order_id}'.replaceAll('{' r'order_id' '}', Uri.encodeComponent(orderId.toString()),);
     final _options = Options(
       method: r'GET',
       headers: <String, dynamic>{
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-freezed/lib/src/api/user_api.dart b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-freezed/lib/src/api/user_api.dart
index ad5d89369ea4..0076a6f55775 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-freezed/lib/src/api/user_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-freezed/lib/src/api/user_api.dart
@@ -250,7 +250,7 @@ class UserApi {
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/user/{username}'.replaceAll('{' r'username' '}', username.toString());
+    final _path = r'/user/{username}'.replaceAll('{' r'username' '}', Uri.encodeComponent(username.toString()),);
     final _options = Options(
       method: r'DELETE',
       headers: <String, dynamic>{
@@ -297,7 +297,7 @@ class UserApi {
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/user/{username}'.replaceAll('{' r'username' '}', username.toString());
+    final _path = r'/user/{username}'.replaceAll('{' r'username' '}', Uri.encodeComponent(username.toString()),);
     final _options = Options(
       method: r'GET',
       headers: <String, dynamic>{
@@ -496,7 +496,7 @@ _responseData = rawData == null ? null : deserialize<String, String>(rawData, 'S
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/user/{username}'.replaceAll('{' r'username' '}', username.toString());
+    final _path = r'/user/{username}'.replaceAll('{' r'username' '}', Uri.encodeComponent(username.toString()),);
     final _options = Options(
       method: r'PUT',
       headers: <String, dynamic>{
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-freezed/pubspec.yaml b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-freezed/pubspec.yaml
index 5bde8eacee67..4d08924131e1 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-freezed/pubspec.yaml
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-freezed/pubspec.yaml
@@ -16,4 +16,11 @@ dev_dependencies:
   build_runner: any
   freezed: '^3.0.0'
   json_serializable: '^6.9.3'
+  # unlike the json_serializable variant, this one has no copy_with_extension_gen
+  # whose source_gen constraint would hold source_helper back; source_helper 1.4.0
+  # added extension members that clash with json_serializable 6.x's internal
+  # copies and break the build_runner build script, so hold it below 1.4.0.
+  # 1.3.9+ requires Dart 3.9 while this variant advertises >=3.8.0, so keep the
+  # 1.3.8 lower bound resolvable for 3.8 users
+  source_helper: '>=1.3.8 <1.4.0'
   test: '^1.16.0'
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/pet_api.dart b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/pet_api.dart
index 60aaece86905..56b029ed8ca0 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/pet_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/pet_api.dart
@@ -114,7 +114,7 @@ class PetApi {
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/pet/{petId}'.replaceAll('{' r'petId' '}', petId.toString());
+    final _path = r'/pet/{petId}'.replaceAll('{' r'petId' '}', Uri.encodeComponent(petId.toString()),);
     final _options = Options(
       method: r'DELETE',
       headers: <String, dynamic>{
@@ -332,7 +332,7 @@ _responseData = rawData == null ? null : deserialize<Set<Pet>, Pet>(rawData, 'Se
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/pet/{petId}'.replaceAll('{' r'petId' '}', petId.toString());
+    final _path = r'/pet/{petId}'.replaceAll('{' r'petId' '}', Uri.encodeComponent(petId.toString()),);
     final _options = Options(
       method: r'GET',
       headers: <String, dynamic>{
@@ -486,7 +486,7 @@ _responseData = rawData == null ? null : deserialize<Pet, Pet>(rawData, 'Pet', g
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/pet/{petId}'.replaceAll('{' r'petId' '}', petId.toString());
+    final _path = r'/pet/{petId}'.replaceAll('{' r'petId' '}', Uri.encodeComponent(petId.toString()),);
     final _options = Options(
       method: r'POST',
       headers: <String, dynamic>{
@@ -564,7 +564,7 @@ _responseData = rawData == null ? null : deserialize<Pet, Pet>(rawData, 'Pet', g
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/pet/{petId}/uploadImage'.replaceAll('{' r'petId' '}', petId.toString());
+    final _path = r'/pet/{petId}/uploadImage'.replaceAll('{' r'petId' '}', Uri.encodeComponent(petId.toString()),);
     final _options = Options(
       method: r'POST',
       headers: <String, dynamic>{
@@ -667,7 +667,7 @@ _responseData = rawData == null ? null : deserialize<ApiResponse, ApiResponse>(r
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/fake/{petId}/uploadImageWithRequiredFile'.replaceAll('{' r'petId' '}', petId.toString());
+    final _path = r'/fake/{petId}/uploadImageWithRequiredFile'.replaceAll('{' r'petId' '}', Uri.encodeComponent(petId.toString()),);
     final _options = Options(
       method: r'POST',
       headers: <String, dynamic>{
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/store_api.dart b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/store_api.dart
index 272e45a0ef6c..4ffc14056b5a 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/store_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/store_api.dart
@@ -40,7 +40,7 @@ class StoreApi {
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/store/order/{order_id}'.replaceAll('{' r'order_id' '}', orderId.toString());
+    final _path = r'/store/order/{order_id}'.replaceAll('{' r'order_id' '}', Uri.encodeComponent(orderId.toString()),);
     final _options = Options(
       method: r'DELETE',
       headers: <String, dynamic>{
@@ -164,7 +164,7 @@ _responseData = rawData == null ? null : deserialize<Map<String, int>, int>(rawD
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/store/order/{order_id}'.replaceAll('{' r'order_id' '}', orderId.toString());
+    final _path = r'/store/order/{order_id}'.replaceAll('{' r'order_id' '}', Uri.encodeComponent(orderId.toString()),);
     final _options = Options(
       method: r'GET',
       headers: <String, dynamic>{
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/user_api.dart b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/user_api.dart
index 87ceeccc6b4a..166786eed585 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/user_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/user_api.dart
@@ -238,7 +238,7 @@ class UserApi {
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/user/{username}'.replaceAll('{' r'username' '}', username.toString());
+    final _path = r'/user/{username}'.replaceAll('{' r'username' '}', Uri.encodeComponent(username.toString()),);
     final _options = Options(
       method: r'DELETE',
       headers: <String, dynamic>{
@@ -285,7 +285,7 @@ class UserApi {
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/user/{username}'.replaceAll('{' r'username' '}', username.toString());
+    final _path = r'/user/{username}'.replaceAll('{' r'username' '}', Uri.encodeComponent(username.toString()),);
     final _options = Options(
       method: r'GET',
       headers: <String, dynamic>{
@@ -484,7 +484,7 @@ _responseData = rawData == null ? null : deserialize<String, String>(rawData, 'S
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/user/{username}'.replaceAll('{' r'username' '}', username.toString());
+    final _path = r'/user/{username}'.replaceAll('{' r'username' '}', Uri.encodeComponent(username.toString()),);
     final _options = Options(
       method: r'PUT',
       headers: <String, dynamic>{
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/src/api/pet_api.dart b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/src/api/pet_api.dart
index a4da1c5ff6db..379f664abef8 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/src/api/pet_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/src/api/pet_api.dart
@@ -118,7 +118,7 @@ class PetApi {
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/pet/{petId}'.replaceAll('{' r'petId' '}', encodeQueryParameter(_serializers, petId, const FullType(int)).toString());
+    final _path = r'/pet/{petId}'.replaceAll('{' r'petId' '}', Uri.encodeComponent(encodeQueryParameter(_serializers, petId, const FullType(int)).toString()),);
     final _options = Options(
       method: r'DELETE',
       headers: <String, dynamic>{
@@ -342,7 +342,7 @@ class PetApi {
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/pet/{petId}'.replaceAll('{' r'petId' '}', encodeQueryParameter(_serializers, petId, const FullType(int)).toString());
+    final _path = r'/pet/{petId}'.replaceAll('{' r'petId' '}', Uri.encodeComponent(encodeQueryParameter(_serializers, petId, const FullType(int)).toString()),);
     final _options = Options(
       method: r'GET',
       headers: <String, dynamic>{
@@ -500,7 +500,7 @@ class PetApi {
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/pet/{petId}'.replaceAll('{' r'petId' '}', encodeQueryParameter(_serializers, petId, const FullType(int)).toString());
+    final _path = r'/pet/{petId}'.replaceAll('{' r'petId' '}', Uri.encodeComponent(encodeQueryParameter(_serializers, petId, const FullType(int)).toString()),);
     final _options = Options(
       method: r'POST',
       headers: <String, dynamic>{
@@ -578,7 +578,7 @@ class PetApi {
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/pet/{petId}/uploadImage'.replaceAll('{' r'petId' '}', encodeQueryParameter(_serializers, petId, const FullType(int)).toString());
+    final _path = r'/pet/{petId}/uploadImage'.replaceAll('{' r'petId' '}', Uri.encodeComponent(encodeQueryParameter(_serializers, petId, const FullType(int)).toString()),);
     final _options = Options(
       method: r'POST',
       headers: <String, dynamic>{
@@ -684,7 +684,7 @@ class PetApi {
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/fake/{petId}/uploadImageWithRequiredFile'.replaceAll('{' r'petId' '}', encodeQueryParameter(_serializers, petId, const FullType(int)).toString());
+    final _path = r'/fake/{petId}/uploadImageWithRequiredFile'.replaceAll('{' r'petId' '}', Uri.encodeComponent(encodeQueryParameter(_serializers, petId, const FullType(int)).toString()),);
     final _options = Options(
       method: r'POST',
       headers: <String, dynamic>{
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/src/api/store_api.dart b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/src/api/store_api.dart
index 6f519ff8ee51..3c3e6ccb8f8d 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/src/api/store_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/src/api/store_api.dart
@@ -43,7 +43,7 @@ class StoreApi {
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/store/order/{order_id}'.replaceAll('{' r'order_id' '}', encodeQueryParameter(_serializers, orderId, const FullType(String)).toString());
+    final _path = r'/store/order/{order_id}'.replaceAll('{' r'order_id' '}', Uri.encodeComponent(encodeQueryParameter(_serializers, orderId, const FullType(String)).toString()),);
     final _options = Options(
       method: r'DELETE',
       headers: <String, dynamic>{
@@ -170,7 +170,7 @@ class StoreApi {
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/store/order/{order_id}'.replaceAll('{' r'order_id' '}', encodeQueryParameter(_serializers, orderId, const FullType(int)).toString());
+    final _path = r'/store/order/{order_id}'.replaceAll('{' r'order_id' '}', Uri.encodeComponent(encodeQueryParameter(_serializers, orderId, const FullType(int)).toString()),);
     final _options = Options(
       method: r'GET',
       headers: <String, dynamic>{
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/src/api/user_api.dart b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/src/api/user_api.dart
index 2a7e5132a60a..f7b22e1a2bf2 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/src/api/user_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/src/api/user_api.dart
@@ -244,7 +244,7 @@ class UserApi {
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/user/{username}'.replaceAll('{' r'username' '}', encodeQueryParameter(_serializers, username, const FullType(String)).toString());
+    final _path = r'/user/{username}'.replaceAll('{' r'username' '}', Uri.encodeComponent(encodeQueryParameter(_serializers, username, const FullType(String)).toString()),);
     final _options = Options(
       method: r'DELETE',
       headers: <String, dynamic>{
@@ -291,7 +291,7 @@ class UserApi {
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/user/{username}'.replaceAll('{' r'username' '}', encodeQueryParameter(_serializers, username, const FullType(String)).toString());
+    final _path = r'/user/{username}'.replaceAll('{' r'username' '}', Uri.encodeComponent(encodeQueryParameter(_serializers, username, const FullType(String)).toString()),);
     final _options = Options(
       method: r'GET',
       headers: <String, dynamic>{
@@ -493,7 +493,7 @@ class UserApi {
     ProgressCallback? onSendProgress,
     ProgressCallback? onReceiveProgress,
   }) async {
-    final _path = r'/user/{username}'.replaceAll('{' r'username' '}', encodeQueryParameter(_serializers, username, const FullType(String)).toString());
+    final _path = r'/user/{username}'.replaceAll('{' r'username' '}', Uri.encodeComponent(encodeQueryParameter(_serializers, username, const FullType(String)).toString()),);
     final _options = Options(
       method: r'PUT',
       headers: <String, dynamic>{