docs: add C# (.NET) SDK as a first-class language

.gitignore

@@ -10,6 +10,10 @@ __pycache__/
 # MkDocs build output
 site/
 
+# .NET build output (from the throwaway C# example compile-check harness)
+[Bb]in/
+[Oo]bj/
+
 # OS files
 .DS_Store
 Thumbs.db
@@ -20,3 +24,6 @@ Thumbs.db
 *~
 .vscode/
 .idea/
+
+# C# example compile-check scratch dir
+.verify/

CONTRIBUTING.md

@@ -32,7 +32,7 @@ Common commands:
 
 1. Create the markdown file in `docs/`
 2. Add the page to the nav section in `zensical.toml`
-3. Create corresponding code examples in all three languages under `examples/`
+3. Create corresponding code examples in all four languages under `examples/`
 4. Test locally with `zensical serve`
 
 ## Vendored dependencies
@@ -152,14 +152,14 @@ Edit documentation in the markdown files under `docs/`.
 
 Embed code samples in documentation pages with the `--8<--` snippet syntax with content tabs for multi-language support.
 
-**IMPORTANT**: All code examples MUST include all three languages (Python, TypeScript, Java) and remain functionally equivalent across languages. The tab order must always be TypeScript → Python → Java.
+**IMPORTANT**: All code examples MUST include all four languages (TypeScript, Python, Java, C#) and remain functionally equivalent across languages. The tab order must always be TypeScript → Python → Java → C#.
 
 #### Steps to add a new code sample:
 
 1. Create example files under `examples/` following the page folder hierarchy
-2. Use identical names with hyphens across all languages (e.g., `retry-with-backoff.{py,ts,java}`)
+2. Use identical names with hyphens across all languages (e.g., `retry-with-backoff.{ts,py,java,cs}`)
 3. Organize by language: `examples/{language}/{section}/{subsection}/{example-name}.{ext}`
-4. Ensure all three language versions demonstrate the same functionality
+4. Ensure all four language versions demonstrate the same functionality
 5. Reference the examples in your documentation using content tabs:
 
 ```markdown
@@ -180,6 +180,12 @@ Embed code samples in documentation pages with the `--8<--` snippet syntax with
     ```java
     --8<-- "examples/java/core/steps/basic-step.java"
     ```
+
+=== "C#"
+
+    ```csharp
+    --8<-- "examples/csharp/core/steps/basic-step.cs"
+    ```
 ```
 
 #### Example structure:
@@ -207,17 +213,28 @@ examples/
 │   └── advanced/
 │       └── error-handling/
 │           └── retry-with-backoff.py
-└── java/
+├── java/
+│   ├── getting-started/
+│   │   └── minimal-example.java
+│   ├── core/
+│   │   ├── steps/
+│   │   │   └── basic-step.java
+│   │   └── parallel/
+│   │       └── parallel-execution.java
+│   └── advanced/
+│       └── error-handling/
+│           └── retry-with-backoff.java
+└── csharp/
     ├── getting-started/
-    │   └── minimal-example.java
+    │   └── minimal-example.cs
     ├── core/
     │   ├── steps/
-    │   │   └── basic-step.java
+    │   │   └── basic-step.cs
     │   └── parallel/
-    │       └── parallel-execution.java
+    │       └── parallel-execution.cs
     └── advanced/
         └── error-handling/
-            └── retry-with-backoff.java
+            └── retry-with-backoff.cs
 ```
 
 This approach keeps code samples maintainable, testable, and consistent across all languages.
@@ -247,7 +264,7 @@ Example:
 ```
 add custom serdes examples
 
-- Add TypeScript, Python, and Java examples for custom
+- Add TypeScript, Python, Java, and C# examples for custom
   serialization
 - Include encryption-at-rest pattern for sensitive data
 - Update serialization doc page with snippet references

README.md

@@ -19,7 +19,7 @@ The `docs/` directory contains the Markdown source files that power the
 documentation site.
 
 Code examples are in `examples/`, organized by language
-(`typescript/`, `python/`, `java/`) and mirroring the docs folder hierarchy.
+(`typescript/`, `python/`, `java/`, `csharp/`) and mirroring the docs folder hierarchy.
 
 Examples are embedded into documentation pages using snippet syntax — see the
 [Contributing Guide](CONTRIBUTING.md) for details.
@@ -63,6 +63,7 @@ for details.
 - [JavaScript SDK Repository](https://github.com/aws/aws-durable-execution-sdk-js)
 - [Python SDK Repository](https://github.com/aws/aws-durable-execution-sdk-python)
 - [Java SDK Repository](https://github.com/aws/aws-durable-execution-sdk-java)
+- [C# SDK Repository](https://github.com/aws/aws-lambda-dotnet/tree/master/Libraries/src/Amazon.Lambda.DurableExecution)
 
 ## Feedback & Support
 

authoring-guide.md

@@ -3,8 +3,8 @@
 This guide covers how to author documentation for AWS Lambda Durable Functions.
 For setup and contribution workflow, see [CONTRIBUTING.md](CONTRIBUTING.md).
 
-Each SDK reference page must be equally useful to TypeScript, Python, and Java
-developers. No language is the implicit default. Language-specific quirks
+Each SDK reference page must be equally useful to TypeScript, Python, Java, and
+C# developers. No language is the implicit default. Language-specific quirks
 belong inside the relevant tab, not in shared prose.
 
 ## Verify Against SDK Source
@@ -26,23 +26,29 @@ For each code example:
 
 ### SDK repositories
 
-You will need the SDK source for all three languages. Clone them alongside
+You will need the SDK source for all four languages. Clone them alongside
 the docs repo:
 
 | Repository | Source path to read |
 |---|---|
 | [aws-durable-execution-sdk-js](https://github.com/aws/aws-durable-execution-sdk-js) | `packages/aws-durable-execution-sdk-js/src` |
 | [aws-durable-execution-sdk-python](https://github.com/aws/aws-durable-execution-sdk-python) | `src/aws_durable_execution_sdk_python` |
 | [aws-durable-execution-sdk-java](https://github.com/aws/aws-durable-execution-sdk-java) | `sdk/src/main/java/software/amazon/lambda/durable` |
+| [aws-lambda-dotnet](https://github.com/aws/aws-lambda-dotnet) | `Libraries/src/Amazon.Lambda.DurableExecution` |
 
 Testing SDKs are useful for confirming example code compiles and runs. The
-JavaScript and Java testing SDKs live in the same repos as the main SDKs
-(under `-testing` package paths). The Python testing SDK lives in a separate
-repo:
+JavaScript, Java, and C# testing SDKs live in the same repos as the main SDKs
+(under `-testing` package paths, or `Amazon.Lambda.DurableExecution.Testing`
+for C#). The Python testing SDK lives in a separate repo:
 
 | Repository | Source path to read |
 |---|---|
 | [aws-durable-execution-sdk-python-testing](https://github.com/aws/aws-durable-execution-sdk-python-testing) | `src/aws_durable_execution_sdk_python_testing` |
+| [aws-lambda-dotnet](https://github.com/aws/aws-lambda-dotnet) | `Libraries/src/Amazon.Lambda.DurableExecution.Testing` |
+
+The C# examples have a local compile-check harness under `scripts/csharp-verify/`
+that builds each example against the SDK DLLs. See that directory's project files
+and `verify.sh`. It is not part of CI.
 
 
 ### Key source files
@@ -53,6 +59,10 @@ repo:
   `StepConfig` and `StepSemantics`. Check `types.py` for `StepContext`.
 - **Java**: `DurableContext.java` for the interface. Check
   `config/StepConfig.java`, `StepContext.java`, `StepSemantics.java`.
+- **C#**: `IDurableContext.cs` for the interface (also defines `IStepContext`,
+  `IExecutionContext`). Check `StepConfig.cs`, `RetryStrategy.cs` (also holds
+  `StepSemantics` and `JitterStrategy`), `DurableFunction.cs` for `WrapAsync`, and
+  the per-operation config types (`CallbackConfig.cs`, `MapConfig.cs`, etc.).
 
 ## Writing Style
 
@@ -149,7 +159,7 @@ as a whole new page can.
 
 ## Language Neutrality
 
-Tab order is always: **TypeScript → Python → Java**.
+Tab order is always: **TypeScript → Python → Java → C#**.
 
 If a language has a quirk, note it inside that language's tab:
 
@@ -177,6 +187,14 @@ If a language has a quirk, note it inside that language's tab:
     ```java
     --8<-- "examples/java/operations/steps/basic-step.java"
     ```
+
+=== "C#"
+
+    The name is optional. Omit it to infer one from the call site.
+
+    ```csharp
+    --8<-- "examples/csharp/operations/steps/basic-step.cs"
+    ```
 ```
 
 ## Page Structure
@@ -185,7 +203,7 @@ SDK reference pages follow this pattern:
 
 1. One or two short paragraphs explaining what the operation does and when
    to use it
-2. A minimal walkthrough example (tabs, all three languages)
+2. A minimal walkthrough example (tabs, all four languages)
 3. Method signature section with per-language tabs
 4. Parameters listed after the tabs (shared where identical, inside tabs
    where language-specific)
@@ -269,7 +287,7 @@ Model tone and structure on these pages:
 
 All code examples must:
 
-- Include all three languages (TypeScript, Python, Java)
+- Include all four languages (TypeScript, Python, Java, C#)
 - Be functionally equivalent across languages
 - Include necessary imports
 - Be minimal. Show the concept, not a full application.
@@ -283,9 +301,10 @@ examples/
   typescript/{section}/{subsection}/{example-name}.ts
   python/{section}/{subsection}/{example-name}.py
   java/{section}/{subsection}/{example-name}.java
+  csharp/{section}/{subsection}/{example-name}.cs
 ```
 
-Use hyphens in filenames. All three languages must have the same set of files.
+Use hyphens in filenames. All four languages must have the same set of files.
 
 ### Embedding in Docs
 
@@ -309,6 +328,12 @@ Use the `--8<--` snippet syntax with content tabs:
     ```java
     --8<-- "examples/java/operations/steps/basic-step.java"
     ```
+
+=== "C#"
+
+    ```csharp
+    --8<-- "examples/csharp/operations/steps/basic-step.cs"
+    ```
 ```
 
 ### Method Signatures
@@ -411,12 +436,13 @@ graph LR
 - [ ] All prose is language-neutral (no Python-only concepts described as universal)
 - [ ] No Table of Contents, no "Back to top" links, no "Back to X" links
 - [ ] No Terminology, Key Features, Best Practices, or FAQ sections
-- [ ] Tab order is TypeScript → Python → Java everywhere
+- [ ] Tab order is TypeScript → Python → Java → C# everywhere
 - [ ] Language-specific notes are inside tabs, not outside
-- [ ] All three languages have example files for every `--8<--` reference
+- [ ] All four languages have example files for every `--8<--` reference
 - [ ] Every example verified against the actual SDK source
 - [ ] Java method signatures show both sync and async variants
 - [ ] TypeScript signatures show both overloads where they exist
+- [ ] C# examples compile via `scripts/csharp-verify/verify.sh`
 - [ ] No emdash, no hyphen-as-dash
 - [ ] No passive voice
 - [ ] Updates are revisions, not tacked-on additions

docs/getting-started/key-concepts.md

@@ -55,6 +55,12 @@ Your durable function receives a `DurableContext` instead of the default Lambda
     --8<-- "examples/java/getting-started/durable-context.java"
     ```
 
+=== "C#"
+
+    ```csharp
+    --8<-- "examples/csharp/getting-started/durable-context.cs"
+    ```
+
 ## Operations
 
 Operations are units of work in a durable execution. Each operation type serves a
@@ -172,6 +178,12 @@ Let's trace through a simple workflow:
     --8<-- "examples/java/getting-started/execution-model.java"
     ```
 
+=== "C#"
+
+    ```csharp
+    --8<-- "examples/csharp/getting-started/execution-model.cs"
+    ```
+
 **First invocation (t=0s):**
 
 1. You start a durable execution by invoking a durable function

docs/getting-started/manage-executions.md

@@ -37,7 +37,7 @@ aws lambda stop-durable-execution \
 
 After updating your code, publish a new version and point your alias to it.
 
-=== "Zip (TypeScript/Python)"
+=== "Zip (TypeScript/Python/C#)"
 
     ```console
     aws lambda update-function-code \

docs/getting-started/quickstart.md

@@ -1,7 +1,7 @@
 # Quickstart
 
 Create and deploy your first durable function using the AWS CLI. This guide covers
-TypeScript, Python, and Java.
+TypeScript, Python, Java, and C#.
 
 !!! note "Adding all your dependencies to the deployment package"
 
@@ -28,6 +28,10 @@ TypeScript, Python, and Java.
 
     - Java 17+ and Maven 3.8+
 
+=== "C#"
+
+    - .NET 10 SDK
+
 ## Create the execution role
 
 Create an IAM role that grants your function permission to perform checkpoint
@@ -93,6 +97,18 @@ Note the role ARN returned. You'll need it in the next step.
     --8<-- "examples/java/getting-started/quickstart.java"
     ```
 
+=== "C#"
+
+    Save as `Function.cs`
+
+    ```csharp
+    --8<-- "examples/csharp/getting-started/quickstart.cs"
+    ```
+
+    This shows the workflow and handler. For the entry point (`Main` +
+    `LambdaBootstrap` + serializer), the class-library alternative, and the full
+    project setup, see the [C# SDK guide](../sdk-reference/languages/csharp/index.md).
+
 The wait here is for 10 seconds just for an easy quick example, but it could as easily
 be 10 days without incurring extra compute.
 
@@ -190,6 +206,31 @@ execution role you just created.
       --durable-config '{"ExecutionTimeout": 900, "RetentionPeriodInDays": 1}'
     ```
 
+=== "C#"
+
+    Add the SDK to your project, then publish and package the output:
+
+    ```console
+    dotnet add package Amazon.Lambda.DurableExecution
+
+    dotnet publish -c Release -o publish
+    cd publish && zip -r ../function.zip . && cd ..
+
+    aws lambda create-function \
+      --function-name my-durable-function \
+      --runtime dotnet10 \
+      --role arn:aws:iam::123456789012:role/durable-function-role \
+      --handler MyDurableFunction \
+      --zip-file fileb://function.zip \
+      --durable-config '{"ExecutionTimeout": 900, "RetentionPeriodInDays": 1}'
+    ```
+
+    The `--handler` value depends on your programming model: the assembly name for
+    the executable model, or `Assembly::Namespace.Type::Method` for a class library.
+    See the
+    [C# SDK guide](../sdk-reference/languages/csharp/index.md) for the programming
+    models, serializer registration, and handler string for each.
+
 ### Publish a version
 
 You must invoke a durable functions with a published version or alias to ensure

docs/index.md

@@ -3,7 +3,7 @@
 !!! note
 
     This guide covers the **AWS Durable Execution SDK**, the client library you use to write
-    durable functions in TypeScript, Python, and Java. For service-level topics including
+    durable functions in TypeScript, Python, Java, and C#. For service-level topics including
     IAM permissions, service quotas, infrastructure-as-code configuration, and monitoring,
     see
     [Lambda durable functions](https://docs.aws.amazon.com/lambda/latest/dg/durable-functions.html)
@@ -60,6 +60,8 @@ For detailed programming language reference, see [SDK Reference](sdk-reference/)
         [aws-durable-execution-sdk-python](https://github.com/aws/aws-durable-execution-sdk-python)
     - :simple-github:
         [aws-durable-execution-sdk-java](https://github.com/aws/aws-durable-execution-sdk-java)
+    - :simple-github:
+        [aws-lambda-dotnet (C#)](https://github.com/aws/aws-lambda-dotnet/tree/master/Libraries/src/Amazon.Lambda.DurableExecution)
 
 ## Related documentation