[Fusion] Add defer support

AGENTS.md

@@ -56,6 +56,7 @@ dotnet test src/HotChocolate/Fusion
 - Use test naming format: `Method_Should_Outcome_When_Condition`.
 - Do not write vacuous assertions (`Assert.NotNull` alone is not a complete test).
 - If a test requires excessive stubs and reflection, use a more appropriate test tier.
+- Do not use em dash style sentences in docs, comments, or XML documentation. Use commas, periods, parentheses, or colons instead.
 
 ### Testing
 

CLAUDE.md

@@ -47,20 +47,36 @@ dotnet test src/HotChocolate/Fusion
 
 ### C# / .NET
 
-- Always use curly braces for loops and conditionals — no exceptions
+- Always use curly braces for loops and conditionals, no exceptions
 - File-scoped namespaces, 4-space indent
 - Test naming: `Method_Should_Outcome_When_Condition`
 - No vacuous assertions (`Assert.NotNull` alone is not a test)
 - If you need 8 stubs + reflection, you're at the wrong test tier
+- Do not use em dash style sentences in docs, comments, or XML documentation. Use commas, periods, parentheses, or colons instead.
 
 ### Testing
 
-- Prefer snapshot tests over manual `Assert` calls — use **CookieCrumble** for snapshots
+- Prefer snapshot tests over manual `Assert` calls, use **CookieCrumble** for snapshots
 - CookieCrumble has native snapshot support for `IExecutionResult`, `GraphQLHttpResponse`, and other core types
 - For smaller snapshots, prefer **inline snapshots** (`MatchInlineSnapshot`) over snapshot files
 - For tests with multiple assertions, use **Markdown snapshots** (`MatchMarkdownSnapshot`)
+- Hard limit: a single test method must contain at most 5 `Assert.*` calls. Anything beyond that is too hard to reason about in review, switch to a snapshot (Markdown for multi-shape state, inline or file for a single output)
+- Use the AAA section marker style. Each section starts with a single-line comment, the test name documents intent, no paragraph-style block comments above sections:
+
+  ```csharp
+  // arrange
+  // optional one-line description, only when the next code is non-obvious
+  ... arrange code ...
+
+  // act
+  ... act code ...
+
+  // assert
+  ... assert code ...
+  ```
+
 - Snapshot tests: update from `__mismatch__/` directory, understand ordering issues before updating
-- Filter tests during iteration — never run the full suite unnecessarily
+- Filter tests during iteration, never run the full suite unnecessarily
 - Real databases in integration tests, not mocks (unless explicitly instructed otherwise)
 
 ## Performance