Document GraphQL test string conventions

Author: spawnia

.claude/CLAUDE.md

@@ -77,6 +77,14 @@ Multiple service providers for optional features (auto-discovered via composer.j
 
 Tests use `Tests\Utils\` namespace for test fixtures (Models, Queries, Mutations, etc.).
 
+### GraphQL string style in tests
+
+- Always annotate GraphQL literals with `/** @lang GraphQL */`.
+- Default to nowdoc: `<<<'GRAPHQL'`.
+- Use heredoc: `<<<GRAPHQL` only if interpolation is required.
+- Avoid quoted multiline GraphQL strings.
+- Preserve intentional indentation/whitespace in schema and assertion-sensitive tests.
+
 ## Code Style
 
 - PHPStan level 8

CONTRIBUTING.md

@@ -128,6 +128,16 @@ $user = User::create([
 ]);
 ```
 
+### GraphQL strings in tests
+
+Use a consistent representation for GraphQL literals in tests:
+
+- Use `/** @lang GraphQL */` before GraphQL string literals.
+- Use nowdoc (`<<<'GRAPHQL'`) for static GraphQL content.
+- Use heredoc (`<<<GRAPHQL`) only when interpolation is required.
+- Prefer nowdoc/heredoc over quoted multiline strings.
+- For schema/assertion cases where whitespace matters, keep indentation deliberate and stable.
+
 ## Working with proto files
 
 Lighthouse uses [protobuf](https://developers.google.com/protocol-buffers) files for [federated tracing](src/Tracing/FederatedTracing/reports.proto).