ix(macros)!: require explicit `.into()` on chain function return values

34 files changed, 177 insertions, 222 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 17c0596..fb0cc85 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -160,6 +160,37 @@ None
 
     All examples, docs, and test cases across the repository have been updated to use the new pattern: creating a `RenderResult` with `RenderResult::new()` or `RenderResult::default()`, writing with `write!`/`writeln!` from `std::io::Write`, and returning the result.
 
+2. **[`macros:chain`]** The `#[chain]` macro's return type requirement has been relaxed. Previously, chain functions were required to return `Next` or `()` (with `()` auto-converting to `ResultEmpty`). Now, chain functions can also return `ChainProcess<ThisProgram>` directly, or omit the return type entirely (which defaults to `()` → `ResultEmpty`).
+
+    The return value of chain functions is now wrapped in an explicit `.into()` call inside the generated `proc` function, ensuring consistent conversion to `ChainProcess<ProgramType>`. As a result, **all downstream code that previously relied on implicit conversion from packed types to `Next`/`ChainProcess` must now call `.into()` explicitly**.
+
+    ```rust
+    // Before — implicit conversion worked because the generated proc
+    // function was `fn proc(...) -> impl Into<ChainProcess<...>>`
+    #[chain]
+    fn handle_greet(args: EntryGreet) -> Next {
+        let name = /* ... */;
+        ResultGreeting::new(name) // implicitly converted
+    }
+
+    // After — the generated proc function is `fn proc(...) -> ChainProcess<...>`,
+    // so the body must produce ChainProcess explicitly
+    #[chain]
+    fn handle_greet(args: EntryGreet) -> Next {
+        let name = /* ... */;
+        ResultGreeting::new(name).into() // explicit conversion required
+    }
+    ```
+
+    The key advantage of this design is that **the original function body and the expanded `proc` function body are now identical** — the macro only adjusts the function signature and inserts an outermost `.into()` wrapper, without rewriting the internal return expressions. This means the semantics of the original code are perfectly preserved: there is no invisible type coercion happening mid-body, and the behavior you write in the source is exactly what executes at runtime. If a bug arises, the expanded code mirrors the source almost one-to-one, making debugging straightforward.
+
+    This change also applies to:
+    - Chain functions returning `()` (unit), where the body's final expression with `.into()` is replaced by an explicit `ResultEmpty::to_chain()` call.
+    - Chain functions using `&mut` resource injection with non-unit returns: the inner closure now calls `__modify_res_and_return_route` (which returns `ChainProcess<C>` directly) instead of relying on `.into()` conversion.
+    - The `__modify_res_and_return_route` method signature changed from accepting `impl Into<ChainProcess<C>>` to returning `ChainProcess<C>` directly.
+
+    All examples, docs, and test cases across the repository have been updated to use `.into()` where packed types are returned from chain functions.
+
 ---
 
 ## Release 0.2.2 (2026-07-10)
diff --git a/README.md b/README.md
index 50c66c6..f67e6d4 100644
--- a/README.md
+++ b/README.md
@@ -166,7 +166,7 @@ fn handle_greet(args: EntryGreet) -> Next {
         .first()
         .cloned()
         .unwrap_or_else(|| "World".to_string());
-    ResultGreeting::new(greeting)
+    ResultGreeting::new(greeting).into()
 }
 ```
 
@@ -234,7 +234,7 @@ fn handle_greet(args: EntryGreet) -> Next {
         .pick::<String>(())                   // positional: first string
         .pick_or::<u8>(["-r", "--repeat"], 1) // optional flag with default
         .unpack();
-    ResultGreeting::new(format!("{} x{}", name, count))
+    ResultGreeting::new(format!("{} x{}", name, count)).into()
 }
 ```
 
@@ -252,7 +252,7 @@ fn handle(args: EntryGreet) -> Next {
         .pick::<Option<String>>(())
         .pick_or::<u8>(["-r", "--repeat"], 1)
         .unpack();
-    ResultGreeting::new(format!("{} x{}", name.unwrap_or_default(), count))
+    ResultGreeting::new(format!("{} x{}", name.unwrap_or_default(), count)).into()
 }
 ```
 
@@ -279,7 +279,7 @@ impl PickableEnum for Language {}
 #[chain]
 fn handle(args: EntryLang) -> Next {
     let lang: Language = args.pick(()).unpack();
-    lang
+    lang.into()
 }
 ```
 
@@ -781,7 +781,7 @@ pack!(ResultDownloaded = String);
 #[chain]
 pub async fn handle_download(args: EntryDownload) -> Next {
     let file = args.pick(()).unpack();
-    download_file(file).await
+    download_file(file).await.into()
 }
 
 async fn download_file(name: String) -> ResultDownloaded {
@@ -843,7 +843,7 @@ fn handle_greet(args: EntryGreet) -> Next {
         .first()
         .cloned()
         .unwrap_or_else(|| "World".to_string());
-    ResultGreeting::new(greeting)
+    ResultGreeting::new(greeting).into()
 }
 
 #[renderer]
diff --git a/docs/_zh_CN/pages/11-resource-system.md b/docs/_zh_CN/pages/11-resource-system.md
index 152e5d6..a8aab4d 100644
--- a/docs/_zh_CN/pages/11-resource-system.md
+++ b/docs/_zh_CN/pages/11-resource-system.md
@@ -57,7 +57,7 @@ fn render_path(result: ResultPath) -> RenderResult {
 #[chain]
 fn handle_visit(_args: EntryVisit, counter: &mut ResVisitCount) -> Next {
     counter.0 += 1;
-    ResultDone::default()
+    ResultDone::default().into()
 }
  
 #[renderer]
diff --git a/docs/_zh_CN/pages/3-define-a-chain.md b/docs/_zh_CN/pages/3-define-a-chain.md
index 7ac5c60..b2850c5 100644
--- a/docs/_zh_CN/pages/3-define-a-chain.md
+++ b/docs/_zh_CN/pages/3-define-a-chain.md
@@ -24,7 +24,7 @@ fn handle_greet(args: EntryGreet) -> Next {
     // args 就是用户输入经过匹配后剩下的参数
     let name = args.inner.first().cloned().unwrap_or_else(|| "World".to_string());
     // 把结果包装成 Next，告诉调度器下一步去哪
-    ResultName::new(name)
+    ResultName::new(name).into()
 }
 ```
  
@@ -88,7 +88,7 @@ fn handle_greet(args: EntryGreet) -> Next {
         .cloned()
         .unwrap_or_else(|| "World".to_string());
  
-    ResultName::new(name)
+    ResultName::new(name).into()
 }
 ```
  
@@ -112,7 +112,7 @@ fn handle_greet(args: EntryGreet) -> Next {
         .first()
         .cloned()
         .unwrap_or_else(|| "World".to_string());
-    ResultName::new(name)
+    ResultName::new(name).into()
 }
  
 fn main() {
diff --git a/docs/_zh_CN/pages/4-render-result.md b/docs/_zh_CN/pages/4-render-result.md
index 7cf2d2b..81c5102 100644
--- a/docs/_zh_CN/pages/4-render-result.md
+++ b/docs/_zh_CN/pages/4-render-result.md
@@ -51,7 +51,7 @@ fn handle_greet(args: EntryGreet) -> Next {
         .first()
         .cloned()
         .unwrap_or_else(|| "World".to_string());
-    ResultName::new(name)
+    ResultName::new(name).into()
 }
  
 // 4. 用 Renderer 输出结果
diff --git a/docs/_zh_CN/pages/5-multiple-commands.md b/docs/_zh_CN/pages/5-multiple-commands.md
index 7d2617b..38ce2cf 100644
--- a/docs/_zh_CN/pages/5-multiple-commands.md
+++ b/docs/_zh_CN/pages/5-multiple-commands.md
@@ -20,13 +20,13 @@ pack!(ResultSum = i32);
 #[chain]
 fn handle_greet(args: EntryGreet) -> Next {
     let name = args.inner.first().cloned().unwrap_or_else(|| "World".to_string());
-    ResultGreeting::new(name)
+    ResultGreeting::new(name).into()
 }
  
 #[chain]
 fn handle_add(args: EntryAdd) -> Next {
     let sum: i32 = args.inner.iter().filter_map(|s| s.parse::<i32>().ok()).sum();
-    ResultSum::new(sum)
+    ResultSum::new(sum).into()
 }
  
 #[renderer]
@@ -70,9 +70,9 @@ Sum: 6
 @@@dispatcher!("add", CMDAdd => EntryAdd);
 @@@pack!(ResultGreeting = String);
 @@@pack!(ResultSum = i32);
-@@@#[chain] fn handle_greet(_args: EntryGreet) -> Next { ResultGreeting::new("ok".into()) }
+@@@#[chain] fn handle_greet(_args: EntryGreet) -> Next { ResultGreeting::new("ok".into()).into() }
 @@@#[renderer] fn render_greet(_greeting: ResultGreeting) -> RenderResult { RenderResult::new() }
-@@@#[chain] fn handle_add(_args: EntryAdd) -> Next { ResultSum::new(0) }
+@@@#[chain] fn handle_add(_args: EntryAdd) -> Next { ResultSum::new(0).into() }
 @@@#[renderer] fn render_sum(_sum: ResultSum) -> RenderResult { RenderResult::new() }
 fn main() {
     let mut program = ThisProgram::new();
diff --git a/docs/_zh_CN/pages/6-argument-parse-picker.md b/docs/_zh_CN/pages/6-argument-parse-picker.md
index b41f839..4bf162c 100644
--- a/docs/_zh_CN/pages/6-argument-parse-picker.md
+++ b/docs/_zh_CN/pages/6-argument-parse-picker.md
@@ -32,7 +32,7 @@ features = ["parser"]
 #[chain]
 fn handle_greet_entry(prev: EntryGreet) -> Next {
     let name = prev.pick_or((), "World").unpack();
-    ResultName::new(name)
+    ResultName::new(name).into()
 }
 ```
  
@@ -47,7 +47,7 @@ fn handle_greet_entry(prev: EntryGreet) -> Next {
 @@@#[chain]
 @@@fn handle_greet_entry(prev: EntryGreet) -> Next {
 let name = prev.pick_or((), "World").unpack();
-@@@ResultName::new(name)
+@@@ResultName::new(name).into()
 @@@}
 ```
  
@@ -82,7 +82,7 @@ let name = prev.pick_or((), "World").unpack();
 #[chain]
 fn handle_greet_entry(prev: EntryGreet) -> Next {
     let name = prev.pick_or(["--name", "-n"], "World").unpack();
-    ResultName::new(name)
+    ResultName::new(name).into()
 }
 ```
  
@@ -124,7 +124,7 @@ fn handle_test_entry(prev: EntryTest) -> Next {
         .pick::<u32>(["--id", "-I"])
         .unpack();
  
-    ResultInfo::new((name, age, id))
+    ResultInfo::new((name, age, id)).into()
 }
 ```
  
@@ -199,7 +199,7 @@ let name = match pick_result {
 
 在您使用 `pick` 提取了用户输入后，可以使用 `after` 立刻处理该参数
 
-```rust
+````rust
 // Features: ["parser"]
 @@@dispatcher!("greet", CMDGreet => EntryGreet);
 @@@pack!(ResultName = String);
@@ -217,7 +217,7 @@ fn handle_greet_entry(prev: EntryGreet) -> Next {
         })
         .unpack();
  
-    ResultName::new(name)
+    ResultName::new(name).into()
 }
 ```
  
@@ -338,7 +338,7 @@ impl Pickable for Address {
 #[chain]
 fn handle_connect_entry(prev: EntryConnect) -> Next {
     let address: Address = prev.pick("--addr").unpack();
-    ResultConnected::new(address)
+    ResultConnected::new(address).into()
 }
  
 #[renderer]
@@ -379,7 +379,7 @@ impl PickableEnum for Fruits {}
 #[chain]
 fn handle_eat_entry(prev: EntryEat) -> Next {
     let fruit: Fruits = prev.pick("--fruit").unpack();
-    ResultFruit::new(fruit)
+    ResultFruit::new(fruit).into()
 }
  
 #[renderer]
diff --git a/docs/_zh_CN/pages/advanced/2-structural-renderer.md b/docs/_zh_CN/pages/advanced/2-structural-renderer.md
index 9a4f111..6b6b0f9 100644
--- a/docs/_zh_CN/pages/advanced/2-structural-renderer.md
+++ b/docs/_zh_CN/pages/advanced/2-structural-renderer.md
@@ -37,7 +37,7 @@ pack_structural!(ResultInfo = (String, i32));
 fn handle_render(args: EntryRender) -> Next {
     let name = args.inner.first().cloned().unwrap_or_default();
     let age = args.inner.get(1).and_then(|s| s.parse().ok()).unwrap_or(0);
-    ResultInfo::new((name, age))
+    ResultInfo::new((name, age)).into()
 }
  
 #[renderer]
diff --git a/docs/_zh_CN/pages/other/features.md b/docs/_zh_CN/pages/other/features.md
index bfd9efc..d92e597 100644
--- a/docs/_zh_CN/pages/other/features.md
+++ b/docs/_zh_CN/pages/other/features.md
@@ -24,7 +24,7 @@ pack!(StateFoo = ());
  
 #[chain]
 async fn handle_state_foo(foo: StateFoo) -> Next {
-    StateFoo::new(())
+    StateFoo::new(()).into()
 }
 ```
  
@@ -160,7 +160,7 @@ use mingling::macros::entry;
 pack!(EntryHello = Vec<String>);
  
 fn main() {
-    let result = handle_hello(entry!("--name", "Bob")).into();
+    let result: Next = handle_hello(entry!("--name", "Bob")).into();
     // ... 此处为断言逻辑
 }
  
diff --git a/docs/pages/11-resource-system.md b/docs/pages/11-resource-system.md
index bc2197f..9491212 100644
--- a/docs/pages/11-resource-system.md
+++ b/docs/pages/11-resource-system.md
@@ -57,7 +57,7 @@ Use `&mut T` to inject a mutable resource:
 #[chain]
 fn handle_visit(_args: EntryVisit, counter: &mut ResVisitCount) -> Next {
     counter.0 += 1;
-    ResultDone::default()
+    ResultDone::default().into()
 }
  
 #[renderer]
diff --git a/docs/pages/3-define-a-chain.md b/docs/pages/3-define-a-chain.md
index c6d3f8e..b2822bc 100644
--- a/docs/pages/3-define-a-chain.md
+++ b/docs/pages/3-define-a-chain.md
@@ -24,7 +24,7 @@ fn handle_greet(args: EntryGreet) -> Next {
     // args contains the remaining params after matching user input
     let name = args.inner.first().cloned().unwrap_or_else(|| "World".to_string());
     // Wrap the result into Next, telling the dispatcher where to go next
-    ResultName::new(name)
+    ResultName::new(name).into()
 }
 ```
  
@@ -88,7 +88,7 @@ fn handle_greet(args: EntryGreet) -> Next {
         .cloned()
         .unwrap_or_else(|| "World".to_string());
  
-    ResultName::new(name)
+    ResultName::new(name).into()
 }
 ```
  
@@ -112,7 +112,7 @@ fn handle_greet(args: EntryGreet) -> Next {
         .first()
         .cloned()
         .unwrap_or_else(|| "World".to_string());
-    ResultName::new(name)
+    ResultName::new(name).into()
 }
  
 fn main() {
diff --git a/docs/pages/4-render-result.md b/docs/pages/4-render-result.md
index b1365b8..ca1e563 100644
--- a/docs/pages/4-render-result.md
+++ b/docs/pages/4-render-result.md
@@ -51,7 +51,7 @@ fn handle_greet(args: EntryGreet) -> Next {
         .first()
         .cloned()
         .unwrap_or_else(|| "World".to_string());
-    ResultName::new(name)
+    ResultName::new(name).into()
 }
  
 // 4. Output results with a Renderer
diff --git a/docs/pages/5-multiple-commands.md b/docs/pages/5-multiple-commands.md
index a56f7b0..d9a335a 100644
--- a/docs/pages/5-multiple-commands.md
+++ b/docs/pages/5-multiple-commands.md
@@ -20,13 +20,13 @@ pack!(ResultSum = i32);
 #[chain]
 fn handle_greet(args: EntryGreet) -> Next {
     let name = args.inner.first().cloned().unwrap_or_else(|| "World".to_string());
-    ResultGreeting::new(name)
+    ResultGreeting::new(name).into()
 }
  
 #[chain]
 fn handle_add(args: EntryAdd) -> Next {
     let sum: i32 = args.inner.iter().filter_map(|s| s.parse::<i32>().ok()).sum();
-    ResultSum::new(sum)
+    ResultSum::new(sum).into()
 }
  
 #[renderer]
@@ -70,9 +70,9 @@ Notice `with_dispatchers`? When you need to register multiple dispatchers, just
 @@@dispatcher!("add", CMDAdd => EntryAdd);
 @@@pack!(ResultGreeting = String);
 @@@pack!(ResultSum = i32);
-@@@#[chain] fn handle_greet(_args: EntryGreet) -> Next { ResultGreeting::new("ok".into()) }
+@@@#[chain] fn handle_greet(_args: EntryGreet) -> Next { ResultGreeting::new("ok".into()).into() }
 @@@#[renderer] fn render_greet(_greeting: ResultGreeting) -> RenderResult { RenderResult::new() }
-@@@#[chain] fn handle_add(_args: EntryAdd) -> Next { ResultSum::new(0) }
+@@@#[chain] fn handle_add(_args: EntryAdd) -> Next { ResultSum::new(0).into() }
 @@@#[renderer] fn render_sum(_sum: ResultSum) -> RenderResult { RenderResult::new() }
 fn main() {
     let mut program = ThisProgram::new();
diff --git a/docs/pages/6-argument-parse-picker.md b/docs/pages/6-argument-parse-picker.md
index c80c25c..398cd3c 100644
--- a/docs/pages/6-argument-parse-picker.md
+++ b/docs/pages/6-argument-parse-picker.md
@@ -32,7 +32,7 @@ Now let's look at `Picker` in action:
 #[chain]
 fn handle_greet_entry(prev: EntryGreet) -> Next {
     let name = prev.pick_or((), "World").unpack();
-    ResultName::new(name)
+    ResultName::new(name).into()
 }
 ```
  
@@ -47,7 +47,7 @@ Breaking down the example above:
 @@@#[chain]
 @@@fn handle_greet_entry(prev: EntryGreet) -> Next {
 let name = prev.pick_or((), "World").unpack();
-@@@ResultName::new(name)
+@@@ResultName::new(name).into()
 @@@}
 ```
  
@@ -82,7 +82,7 @@ If your program needs to parse flag args (e.g., `greet --name Alice`), do this:
 #[chain]
 fn handle_greet_entry(prev: EntryGreet) -> Next {
     let name = prev.pick_or(["--name", "-n"], "World").unpack();
-    ResultName::new(name)
+    ResultName::new(name).into()
 }
 ```
  
@@ -124,7 +124,7 @@ fn handle_test_entry(prev: EntryTest) -> Next {
         .pick::<u32>(["--id", "-I"])
         .unpack();
  
-    ResultInfo::new((name, age, id))
+    ResultInfo::new((name, age, id)).into()
 }
 ```
  
@@ -224,7 +224,7 @@ fn handle_greet_entry(prev: EntryGreet) -> Next {
         })
         .unpack();
  
-    ResultName::new(name)
+    ResultName::new(name).into()
 }
 ```
  
@@ -345,7 +345,7 @@ impl Pickable for Address {
 #[chain]
 fn handle_connect_entry(prev: EntryConnect) -> Next {
     let address: Address = prev.pick("--addr").unpack();
-    ResultConnected::new(address)
+    ResultConnected::new(address).into()
 }
  
 #[renderer]
@@ -387,7 +387,7 @@ impl PickableEnum for Fruits {}
 #[chain]
 fn handle_eat_entry(prev: EntryEat) -> Next {
     let fruit: Fruits = prev.pick("--fruit").unpack();
-    ResultFruit::new(fruit)
+    ResultFruit::new(fruit).into()
 }
  
 #[renderer]
diff --git a/docs/pages/advanced/2-structural-renderer.md b/docs/pages/advanced/2-structural-renderer.md
index f31f758..fab7530 100644
--- a/docs/pages/advanced/2-structural-renderer.md
+++ b/docs/pages/advanced/2-structural-renderer.md
@@ -37,7 +37,7 @@ pack_structural!(ResultInfo = (String, i32));
 fn handle_render(args: EntryRender) -> Next {
     let name = args.inner.first().cloned().unwrap_or_default();
     let age = args.inner.get(1).and_then(|s| s.parse().ok()).unwrap_or(0);
-    ResultInfo::new((name, age))
+    ResultInfo::new((name, age)).into()
 }
  
 #[renderer]
diff --git a/docs/pages/other/features.md b/docs/pages/other/features.md
index 813ccdd..325bb75 100644
--- a/docs/pages/other/features.md
+++ b/docs/pages/other/features.md
@@ -24,7 +24,7 @@ pack!(StateFoo = ());
  
 #[chain]
 async fn handle_state_foo(foo: StateFoo) -> Next {
-    StateFoo::new(())
+    StateFoo::new(()).into()
 }
 ```
  
@@ -160,7 +160,7 @@ use mingling::macros::entry;
 pack!(EntryHello = Vec<String>);
  
 fn main() {
-    let result = handle_hello(entry!("--name", "Bob")).into();
+    let result: Next = handle_hello(entry!("--name", "Bob")).into();
     // ... assertion logic here
 }
  
diff --git a/examples/example-argument-parse/src/main.rs b/examples/example-argument-parse/src/main.rs
index 59499a2..eb07672 100644
--- a/examples/example-argument-parse/src/main.rs
+++ b/examples/example-argument-parse/src/main.rs
@@ -46,7 +46,7 @@ fn handle_transfer_parse(args: EntryTransfer) -> Next {
         // Convert into ResultFile
         .into();
     // --------- IMPORTANT ---------
-    result
+    result.into()
 }
 
 pack!(ErrorNoNameProvided = ());
diff --git a/examples/example-async-support/src/main.rs b/examples/example-async-support/src/main.rs
index ac85aaf..af86408 100644
--- a/examples/example-async-support/src/main.rs
+++ b/examples/example-async-support/src/main.rs
@@ -50,7 +50,7 @@ pack!(ResultDownloaded = String);
 //  vvvvv_ `async` keyword can be used directly here
 pub async fn handle_download(args: EntryDownload) -> Next {
     let file_name = args.pick(()).unpack();
-    fake_download(file_name).await
+    fake_download(file_name).await.into()
 }
 
 /// Renders the downloaded file name.
diff --git a/examples/example-basic/src/main.rs b/examples/example-basic/src/main.rs
index 7fc0bce..17077e2 100644
--- a/examples/example-basic/src/main.rs
+++ b/examples/example-basic/src/main.rs
@@ -55,7 +55,7 @@ fn handle_greet(args: EntryGreet) -> Next {
         .cloned()
         .unwrap_or_else(|| "World".to_string())
         .into();
-    name
+    name.into()
 }
 
 // Define renderer `render_name`, used to render `ResultName`
diff --git a/examples/example-combine-pathf-dispatch-tree/src/sub/mod.rs b/examples/example-combine-pathf-dispatch-tree/src/sub/mod.rs
index 5ab0ece..2b7aba9 100644
--- a/examples/example-combine-pathf-dispatch-tree/src/sub/mod.rs
+++ b/examples/example-combine-pathf-dispatch-tree/src/sub/mod.rs
@@ -14,7 +14,7 @@ pub fn handle_my(args: EntryHello) -> Next {
         .cloned()
         .unwrap_or_else(|| "World".to_string())
         .into();
-    name
+    name.into()
 }
 
 #[renderer]
diff --git a/examples/example-completion/src/main.rs b/examples/example-completion/src/main.rs
index 0159807..45cc8ef 100644
--- a/examples/example-completion/src/main.rs
+++ b/examples/example-completion/src/main.rs
@@ -114,7 +114,7 @@ fn handle_greet(args: EntryGreet) -> Next {
         .pick_or((), "World")
         .unpack()
         .into();
-    result
+    result.into()
 }
 
 /// Renders the greeting with the result name and repeat count.
diff --git a/examples/example-enum-tag/src/main.rs b/examples/example-enum-tag/src/main.rs
index 01c7767..91c5358 100644
--- a/examples/example-enum-tag/src/main.rs
+++ b/examples/example-enum-tag/src/main.rs
@@ -79,7 +79,7 @@ dispatcher!("lang-select", CMDLanguageSelection => EntryLanguageSelection);
 fn handle_language_selection(args: EntryLanguageSelection) -> Next {
     // You can use Picker to directly parse ProgrammingLanguages
     let lang: ProgrammingLanguages = args.pick(()).unpack();
-    lang
+    lang.into()
 }
 
 /// Renders the selected programming language with its name and description.
diff --git a/examples/example-hook/src/main.rs b/examples/example-hook/src/main.rs
index 41928ca..23b87c7 100644
--- a/examples/example-hook/src/main.rs
+++ b/examples/example-hook/src/main.rs
@@ -64,7 +64,7 @@ fn handle_greet(args: EntryGreet) -> Next {
         .cloned()
         .unwrap_or_else(|| "World".to_string())
         .into();
-    name
+    name.into()
 }
 
 /// Renders the greeting message with the provided name.
diff --git a/examples/example-panic-unwind/src/main.rs b/examples/example-panic-unwind/src/main.rs
index a829158..d5f746f 100644
--- a/examples/example-panic-unwind/src/main.rs
+++ b/examples/example-panic-unwind/src/main.rs
@@ -47,7 +47,7 @@ fn handle_panic(prev: EntryPanic) -> Next {
             // Panic happens here, will be caught
             panic!("{}", s)
         }
-        None => NotPanic::default(),
+        None => NotPanic::default().into(),
     }
 }
 
diff --git a/examples/example-pathfinder/src/sub/mod.rs b/examples/example-pathfinder/src/sub/mod.rs
index 6d15930..8cbc1c5 100644
--- a/examples/example-pathfinder/src/sub/mod.rs
+++ b/examples/example-pathfinder/src/sub/mod.rs
@@ -13,7 +13,7 @@ pub fn handle_greet(args: EntryGreet) -> Next {
         .cloned()
         .unwrap_or_else(|| "World".to_string())
         .into();
-    name
+    name.into()
 }
 
 /// Renders the name.
diff --git a/examples/example-repl-basic/src/main.rs b/examples/example-repl-basic/src/main.rs
index d15319e..cfd00d1 100644
--- a/examples/example-repl-basic/src/main.rs
+++ b/examples/example-repl-basic/src/main.rs
@@ -94,7 +94,7 @@ pack!(ResultList = Vec<String>);
 #[chain]
 fn parse_cd_args(prev: EntryCd) -> Next {
     let join = prev.pick(()).unpack();
-    StateChangeDirectory::new(join)
+    StateChangeDirectory::new(join).into()
 }
 
 // Execute directory change
diff --git a/examples/example-resources/src/main.rs b/examples/example-resources/src/main.rs
index b08ee26..60c5c08 100644
--- a/examples/example-resources/src/main.rs
+++ b/examples/example-resources/src/main.rs
@@ -51,7 +51,7 @@ fn render_modify_current(args: EntryModifyCurrent, current_dir: &mut ResCurrentD
     current_dir.current_dir = current_dir
         .current_dir
         .join(args.pick::<String>(()).unpack());
-    EntryCurrent::default()
+    EntryCurrent::default().into()
 }
 
 // Define renderer for output current path       _____________ Injected resource
diff --git a/mingling/src/example_docs.rs b/mingling/src/example_docs.rs
index 4699a50..c4f59c9 100644
--- a/mingling/src/example_docs.rs
+++ b/mingling/src/example_docs.rs
@@ -66,7 +66,7 @@
 ///         // Convert into ResultFile
 ///         .into();
 ///     // --------- IMPORTANT ---------
-///     result
+///     result.into()
 /// }
 ///
 /// pack!(ErrorNoNameProvided = ());
@@ -199,7 +199,7 @@ pub mod example_argument_parse {}
 /// //  vvvvv_ `async` keyword can be used directly here
 /// pub async fn handle_download(args: EntryDownload) -> Next {
 ///     let file_name = args.pick(()).unpack();
-///     fake_download(file_name).await
+///     fake_download(file_name).await.into()
 /// }
 ///
 /// /// Renders the downloaded file name.
@@ -292,7 +292,7 @@ pub mod example_async_support {}
 ///         .cloned()
 ///         .unwrap_or_else(|| "World".to_string())
 ///         .into();
-///     name
+///     name.into()
 /// }
 ///
 /// // Define renderer `render_name`, used to render `ResultName`
@@ -672,7 +672,7 @@ pub mod example_combine_pathf_dispatch_tree {}
 ///         .pick_or((), "World")
 ///         .unpack()
 ///         .into();
-///     result
+///     result.into()
 /// }
 ///
 /// /// Renders the greeting with the result name and repeat count.
@@ -1026,7 +1026,7 @@ pub mod example_dispatch_tree {}
 /// fn handle_language_selection(args: EntryLanguageSelection) -> Next {
 ///     // You can use Picker to directly parse ProgrammingLanguages
 ///     let lang: ProgrammingLanguages = args.pick(()).unpack();
-///     lang
+///     lang.into()
 /// }
 ///
 /// /// Renders the selected programming language with its name and description.
@@ -1428,7 +1428,7 @@ pub mod example_help {}
 ///         .cloned()
 ///         .unwrap_or_else(|| "World".to_string())
 ///         .into();
-///     name
+///     name.into()
 /// }
 ///
 /// /// Renders the greeting message with the provided name.
@@ -1967,7 +1967,7 @@ pub mod example_pack_err {}
 ///             // Panic happens here, will be caught
 ///             panic!("{}", s)
 ///         }
-///         None => NotPanic::default(),
+///         None => NotPanic::default().into(),
 ///     }
 /// }
 ///
@@ -2161,7 +2161,7 @@ pub mod example_pathfinder {}
 /// #[chain]
 /// fn parse_cd_args(prev: EntryCd) -> Next {
 ///     let join = prev.pick(()).unpack();
-///     StateChangeDirectory::new(join)
+///     StateChangeDirectory::new(join).into()
 /// }
 ///
 /// // Execute directory change
@@ -2323,7 +2323,7 @@ pub mod example_repl_basic {}
 ///     current_dir.current_dir = current_dir
 ///         .current_dir
 ///         .join(args.pick::<String>(()).unpack());
-///     EntryCurrent::default()
+///     EntryCurrent::default().into()
 /// }
 ///
 /// // Define renderer for output current path       _____________ Injected resource
diff --git a/mingling/src/lib.md b/mingling/src/lib.md
index cd89b96..03fa61d 100644
--- a/mingling/src/lib.md
+++ b/mingling/src/lib.md
@@ -40,7 +40,7 @@ fn handle_greet(args: EntryGreet) -> Next {
         .cloned()
         .unwrap_or_else(|| "World".to_string())
         .into();
-    name
+    name.into()
 }
 
 #[renderer]
diff --git a/mingling_core/src/asset/global_resource.rs b/mingling_core/src/asset/global_resource.rs
index 3d0af7b..29e1136 100644
--- a/mingling_core/src/asset/global_resource.rs
+++ b/mingling_core/src/asset/global_resource.rs
@@ -45,13 +45,12 @@ where
 
     /// Internal syntax for the `&mut MyResource` syntax of #[chain], do not use directly
     #[doc(hidden)]
-    pub fn __modify_res_and_return_route<Res, Return>(
+    pub fn __modify_res_and_return_route<Res>(
         &self,
-        f: impl FnOnce(&mut Res) -> Return,
-    ) -> impl Into<ChainProcess<C>>
+        f: impl FnOnce(&mut Res) -> ChainProcess<C>,
+    ) -> ChainProcess<C>
     where
         Res: 'static + Default + ResourceMarker + Send + Sync,
-        Return: Into<ChainProcess<C>>,
     {
         let Ok(mut guard) = self.resources.lock() else {
             let mut default_res = Res::res_default();
diff --git a/mingling_macros/src/chain.rs b/mingling_macros/src/chain.rs
index 5f72422..5044227 100644
--- a/mingling_macros/src/chain.rs
+++ b/mingling_macros/src/chain.rs
@@ -9,8 +9,7 @@ use quote::{ToTokens, quote};
 use syn::spanned::Spanned;
 use syn::{Ident, ItemFn, Pat, ReturnType, Signature, Type, TypePath, parse_macro_input};
 
-/// Validates that the return type of the function is `Next`.
-/// Checks whether the return type is `()` (unit).
+/// Checks whether the return type is `()`
 fn is_unit_return_type(sig: &Signature) -> bool {
     match &sig.output {
         ReturnType::Type(_, ty) => match &**ty {
@@ -21,8 +20,9 @@ fn is_unit_return_type(sig: &Signature) -> bool {
     }
 }
 
+/// Validates that the return type is `Next`, `ChainProcess<ThisProgram>`, `()`, or omitted.
 fn validate_return_type(sig: &Signature) -> Result<(), proc_macro2::TokenStream> {
-    // If return type is `()`, it's valid (no Next required)
+    // `()` or omitted is always valid
     if is_unit_return_type(sig) {
         return Ok(());
     }
@@ -31,38 +31,36 @@ fn validate_return_type(sig: &Signature) -> Result<(), proc_macro2::TokenStream>
         ReturnType::Type(_, ty) => match &**ty {
             Type::Path(type_path) => {
                 let last_segment = type_path.path.segments.last().unwrap();
-                if last_segment.ident != "Next" {
-                    return Err(syn::Error::new(
-                        ty.span(),
-                        "Chain function must return `Next` or `()`",
-                    )
-                    .to_compile_error());
+                let ident_str = last_segment.ident.to_string();
+                if ident_str == "Next" || ident_str == "ChainProcess" {
+                    return Ok(());
                 }
-            }
-            _ => {
-                return Err(syn::Error::new(
+                Err(syn::Error::new(
                     ty.span(),
-                    "Chain function must return `Next` or `()`",
+                    "Chain function must return `Next`, `ChainProcess<ThisProgram>`, `()`, or omit the return type",
                 )
-                .to_compile_error());
+                .to_compile_error())
             }
+            _ => Err(syn::Error::new(
+                ty.span(),
+                "Chain function must return `Next`, `ChainProcess<ThisProgram>`, `()`, or omit the return type",
+            )
+            .to_compile_error()),
         },
         ReturnType::Default => {
-            return Err(syn::Error::new(
+            Err(syn::Error::new(
                 sig.span(),
-                "Chain function must specify a return type (must be `Next` or `()`)",
+                "Chain function must specify a return type (must be `Next`, `ChainProcess<ThisProgram>`, or `()`)",
             )
-            .to_compile_error());
+            .to_compile_error())
         }
     }
-    Ok(())
 }
 
-/// Builds the `proc` function implementation that serves as the actual chain
-/// entry point inside the generated `Chain` impl.
+/// Builds the `proc` function implementation inside the generated `Chain` impl.
 ///
-/// * Without resources: delegates directly to the original function.
-/// * With resources: inlines the body and prepends resource bindings.
+/// The user's function body is inlined directly, and its result is converted
+/// via `.into()` to `ChainProcess<ProgramType>`.
 #[allow(unused_variables)]
 fn generate_proc_fn(
     has_resources: bool,
@@ -70,7 +68,6 @@ fn generate_proc_fn(
     program_type: &proc_macro2::TokenStream,
     previous_type: &TypePath,
     prev_param: &Pat,
-    fn_name: &Ident,
     fn_body_stmts: &[syn::Stmt],
     is_async_fn: bool,
     is_unit_return: bool,
@@ -78,59 +75,42 @@ fn generate_proc_fn(
     let immut_resource_stmts = generate_immut_resource_bindings(resources.iter(), program_type);
     let mut_resources: Vec<_> = resources.iter().filter(|r| r.is_mut).collect();
 
-    let body_stmts: &[syn::Stmt] = if is_unit_return && has_resources {
-        let mut stmts = fn_body_stmts.to_vec();
-        stmts.push(syn::Stmt::Expr(
-            syn::parse_quote! {
-                <crate::ResultEmpty as ::mingling::Groupped::<crate::ThisProgram>>
-                ::to_chain(crate::ResultEmpty)
-            },
-            None,
-        ));
-        // Box::leak to get a &'static [syn::Stmt]
-        Box::leak(Box::new(stmts))
-    } else {
-        fn_body_stmts
-    };
-
     let wrapped_body = if is_async_fn && !mut_resources.is_empty() {
-        wrap_body_with_mut_resources_async(body_stmts, &mut_resources, program_type)
+        wrap_body_with_mut_resources_async(fn_body_stmts, &mut_resources, program_type)
     } else {
-        wrap_body_with_mut_resources(body_stmts, &mut_resources, program_type)
+        wrap_body_with_mut_resources(fn_body_stmts, &mut_resources, program_type, is_unit_return)
     };
 
-    // When the function returns `()`, wrap the result with ResultEmpty
-    let call_or_wrapped = if is_unit_return {
-        if has_resources {
+    let proc_body = if is_unit_return {
+        let body_with_ending = if has_resources {
             quote! {
                 #(#immut_resource_stmts)*
-                #wrapped_body
+                #wrapped_body;
+                <crate::ResultEmpty as ::mingling::Groupped::<crate::ThisProgram>>
+                ::to_chain(crate::ResultEmpty)
             }
         } else {
-            let call = if is_async_fn {
-                quote! { #fn_name(#prev_param).await; }
-            } else {
-                quote! { #fn_name(#prev_param); }
-            };
             quote! {
-                #call
+                #wrapped_body;
                 <crate::ResultEmpty as ::mingling::Groupped::<crate::ThisProgram>>
                 ::to_chain(crate::ResultEmpty)
             }
-        }
-    } else if has_resources {
-        quote! {
-            #(#immut_resource_stmts)*
-            #wrapped_body
-        }
+        };
+        quote! { #body_with_ending }
     } else {
-        let call = if is_async_fn {
-            quote! { #fn_name(#prev_param).await.into() }
+        let body = if has_resources {
+            quote! {
+                #(#immut_resource_stmts)*
+                #wrapped_body
+            }
         } else {
-            quote! { #fn_name(#prev_param).into() }
+            quote! { #wrapped_body }
         };
+        // Use a let-binding with explicit type annotation so that the inner
+        // body's `.into()` calls resolve correctly (same as the original function).
         quote! {
-            #call
+            let __chain_result: ::mingling::ChainProcess<#program_type> = { #body };
+            __chain_result
         }
     };
 
@@ -138,7 +118,7 @@ fn generate_proc_fn(
     {
         quote! {
             async fn proc(#prev_param: #previous_type) -> ::mingling::ChainProcess<#program_type> {
-                #call_or_wrapped
+                #proc_body
             }
         }
     }
@@ -147,73 +127,14 @@ fn generate_proc_fn(
     {
         quote! {
             fn proc(#prev_param: #previous_type) -> ::mingling::ChainProcess<#program_type> {
-                #call_or_wrapped
-            }
-        }
-    }
-}
-
-/// Generates the original function signature (kept for backwards compatibility /
-/// internal use), with its return type changed to `impl Into<ChainProcess<..>>`.
-#[allow(unused_variables)]
-fn generate_original_fn(
-    fn_attrs: &[syn::Attribute],
-    vis: &syn::Visibility,
-    fn_name: &Ident,
-    inputs: &syn::punctuated::Punctuated<syn::FnArg, syn::Token![,]>,
-    fn_body: &syn::Block,
-    is_async_fn: bool,
-    program_type: &proc_macro2::TokenStream,
-    is_unit_return: bool,
-) -> proc_macro2::TokenStream {
-    // Both unit and Next return types need to produce `impl Into<ChainProcess<ProgramType>>`
-    let return_type = quote! { impl Into<::mingling::ChainProcess<#program_type>> };
-
-    let body = if is_unit_return {
-        quote! {
-            {
-                #fn_body
-                <crate::ResultEmpty as ::mingling::Groupped::<crate::ThisProgram>>::to_chain(crate::ResultEmpty)
-            }
-        }
-    } else {
-        quote! {
-            {
-                let _: crate::Next;
-                let _: Next;
-                #fn_body
-            }
-        }
-    };
-
-    #[cfg(feature = "async")]
-    {
-        let async_kw = if is_async_fn {
-            quote! { async }
-        } else {
-            quote! {}
-        };
-        quote! {
-            #(#fn_attrs)*
-            #vis #async_kw fn #fn_name(#inputs) -> #return_type {
-                #body
-            }
-        }
-    }
-
-    #[cfg(not(feature = "async"))]
-    {
-        quote! {
-            #(#fn_attrs)*
-            #vis fn #fn_name(#inputs) -> #return_type {
-                #body
+                #proc_body
             }
         }
     }
 }
 
 /// Assembles the final expanded output: hidden struct, `register_chain!` invocation,
-/// `Chain` impl with the `proc` method, and the original function.
+/// `Chain` impl with the `proc` method, and the preserved original function.
 fn generate_struct_and_impl(
     fn_attrs: &[syn::Attribute],
     vis: &syn::Visibility,
@@ -222,7 +143,7 @@ fn generate_struct_and_impl(
     previous_type_str: &proc_macro2::TokenStream,
     program_type: &proc_macro2::TokenStream,
     proc_fn: &proc_macro2::TokenStream,
-    origin_proc_fn: &proc_macro2::TokenStream,
+    original_fn: &proc_macro2::TokenStream,
 ) -> proc_macro2::TokenStream {
     quote! {
         #(#fn_attrs)*
@@ -238,8 +159,8 @@ fn generate_struct_and_impl(
             #proc_fn
         }
 
-        // Keep the original function for internal use
-        #origin_proc_fn
+        // Keep the original function unchanged
+        #original_fn
     }
 }
 
@@ -296,8 +217,6 @@ pub fn chain_attr(attr: TokenStream, item: TokenStream) -> TokenStream {
     };
 
     // Prepare building blocks
-    let sig = &input_fn.sig;
-    let inputs = &sig.inputs;
     let fn_body = &input_fn.block;
     let mut fn_attrs = input_fn.attrs.clone();
     fn_attrs.retain(|attr| !attr.path().is_ident("chain"));
@@ -315,14 +234,13 @@ pub fn chain_attr(attr: TokenStream, item: TokenStream) -> TokenStream {
     // Always use the default crate-defined program path
     let program_type = crate::default_program_path();
 
-    // Generate the `proc` function
+    // Generate the `proc` function for the Chain impl
     let proc_fn = generate_proc_fn(
         has_resources,
         &resources,
         &program_type,
         &previous_type,
         &prev_param,
-        fn_name,
         &fn_body.stmts,
         #[cfg(feature = "async")]
         is_async_fn,
@@ -331,20 +249,14 @@ pub fn chain_attr(attr: TokenStream, item: TokenStream) -> TokenStream {
         is_unit_return,
     );
 
-    // Generate the original function
-    let origin_proc_fn = generate_original_fn(
-        &fn_attrs,
-        vis,
-        fn_name,
-        inputs,
-        fn_body,
-        #[cfg(feature = "async")]
-        is_async_fn,
-        #[cfg(not(feature = "async"))]
-        false,
-        &program_type,
-        is_unit_return,
-    );
+    // Preserve the original function untouched, with dead_code allowed
+    // since it may only be called through the Chain trait dispatch.
+    // Note: do NOT add `#vis` here — `input_fn` (ItemFn) already contains its own visibility.
+    let original_fn = quote! {
+        #[allow(dead_code)]
+        #(#fn_attrs)*
+        #input_fn
+    };
 
     // Assemble the final output
     let previous_type_str = quote! { #previous_type };
@@ -356,7 +268,7 @@ pub fn chain_attr(attr: TokenStream, item: TokenStream) -> TokenStream {
         &previous_type_str,
         &program_type,
         &proc_fn,
-        &origin_proc_fn,
+        &original_fn,
     );
 
     expanded.into()
diff --git a/mingling_macros/src/lib.rs b/mingling_macros/src/lib.rs
index d0f603a..e9fc327 100644
--- a/mingling_macros/src/lib.rs
+++ b/mingling_macros/src/lib.rs
@@ -867,7 +867,8 @@ pub fn dispatcher(input: TokenStream) -> TokenStream {
 ///
 /// - The function must have at least **one** parameter (the previous type in the chain).
 /// - The first parameter must be taken **by move**.
-/// - The function must return `Next` (the type alias generated by `gen_program!`, which equals `ChainProcess<ProgramName>`).
+/// - The function may return `Next`, `ChainProcess<ProgramName>`, `()`, or omit the return type.
+/// - The original function signature is preserved unchanged.
 /// - With the `async` feature, async functions are supported; without it, async functions are rejected.
 #[proc_macro_attribute]
 pub fn chain(attr: TokenStream, item: TokenStream) -> TokenStream {
diff --git a/mingling_macros/src/renderer.rs b/mingling_macros/src/renderer.rs
index 398c025..d124ec9 100644
--- a/mingling_macros/src/renderer.rs
+++ b/mingling_macros/src/renderer.rs
@@ -119,6 +119,7 @@ pub fn renderer_attr(attr: TokenStream, item: TokenStream) -> TokenStream {
         }
 
         // Keep the original function unchanged
+        #[allow(dead_code)]
         #(#fn_attrs)*
         #vis fn #fn_name(#original_inputs) -> #original_return_type {
             #(#fn_body_stmts)*
diff --git a/mingling_macros/src/res_injection.rs b/mingling_macros/src/res_injection.rs
index 09da889..606b9a6 100644
--- a/mingling_macros/src/res_injection.rs
+++ b/mingling_macros/src/res_injection.rs
@@ -163,8 +163,10 @@ fn mut_res_binding_name(var_name: &Ident) -> Ident {
     syn::Ident::new(&format!("__{}_binding", var_name), var_name.span())
 }
 
-/// Wraps the function body in nested `__modify_res_and_return_route` closures for
-/// each mutable resource parameter (sync version).
+/// Wraps the function body in mutable resource closures (sync version).
+///
+/// For unit return types: uses `modify_res` (closure returns `()`).
+/// For non-unit return types: uses `__modify_res_and_return_route` (closure returns `ChainProcess<C>`).
 ///
 /// The innermost closure gets the original body, and each mutable parameter wraps
 /// outward from last to first.
@@ -172,6 +174,7 @@ pub(crate) fn wrap_body_with_mut_resources(
     fn_body_stmts: &[syn::Stmt],
     mut_resources: &[&ResourceInjection],
     program_type: &proc_macro2::TokenStream,
+    is_unit_return: bool,
 ) -> proc_macro2::TokenStream {
     let mut wrapped = quote! {
         #(#fn_body_stmts)*
@@ -180,11 +183,19 @@ pub(crate) fn wrap_body_with_mut_resources(
     for res in mut_resources {
         let var_name = &res.var_name;
         let inner_type = &res.inner_type;
-        wrapped = quote! {
-            ::mingling::this::<#program_type>().__modify_res_and_return_route(|#var_name: &mut #inner_type| {
-                #wrapped
-            }).into()
-        };
+        if is_unit_return {
+            wrapped = quote! {
+                ::mingling::this::<#program_type>().modify_res(|#var_name: &mut #inner_type| {
+                    #wrapped
+                })
+            };
+        } else {
+            wrapped = quote! {
+                ::mingling::this::<#program_type>().__modify_res_and_return_route(|#var_name: &mut #inner_type| {
+                    #wrapped
+                })
+            };
+        }
     }
 
     wrapped