Clarify hash truncation and expected documentId derivation

Agent-Logs-Url: https://github.com/fsprojects/FSharp.Data.GraphQL/sessions/020d0296-28b1-416d-bd12-9dd0790516ba

Co-authored-by: xperiandri <2365592+xperiandri@users.noreply.github.com>

Author: Copilot

src/FSharp.Data.GraphQL.Server/Executor.fs

@@ -83,6 +83,7 @@ type Executor<'Root>(schema: ISchema<'Root>, middlewares : IExecutorMiddleware s
     let middlewaresList = Seq.toList middlewares
 
     /// Generates a deterministic document identifier from the canonical query string.
+    /// The SHA-256 hash is truncated to 32 bits to preserve the existing int32 documentId contract.
     let getDocumentId (document : Document) =
         let canonicalQuery = document.ToQueryString()
         let queryBytes = Encoding.UTF8.GetBytes canonicalQuery

tests/FSharp.Data.GraphQL.Tests/ExecutionTests.fs

@@ -384,7 +384,8 @@ let ``Execution when querying returns unique document id with response`` () =
                     Define.Field("b", IntType, fun _ x -> x.B)
                 ]))
     let query = "query Example { a, b, a }"
-    // Deterministic SHA-256-based documentId for the canonical AST query string above.
+    // Deterministic SHA-256-based documentId for canonical `query Example { a b a }`,
+    // using the first 4 bytes of the hash as a big-endian int32.
     let expectedDocumentId = -2063861555
     let result1 = sync <| Executor(schema).AsyncExecute(query, getMockInputContext, { A = "aa"; B = 2 })
     let result2 = sync <| Executor(schema).AsyncExecute(query, getMockInputContext, { A = "aa"; B = 2 })