[michaelstaib]

When a request was aborted while a @defer branch was still running, its operation context went back to the pool while the deferred resolvers still used it. The next request could rent that context, finish early with missing data, and return a Cannot return null for non-nullable field. error from the old request. Operation contexts now count the tasks created from them, and the pool discards a context that still has tasks outstanding. The defer task also waits for its tasks to be returned before it resets its context.

# request 1, aborted while `slow` runs
{ fast ... @defer { slow } }

# request 2, before this fix
# {"errors":[{"message":"Cannot return null for non-nullable field.","path":["slow"]}],"data":{"fast":"fast-value"}}
{ fast }

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Patch coverage

96.5% of changed lines covered (83/86)

File	Covered	Changed	Patch %
…/src/Types/Execution/Processing/OperationContext.Pooling.cs	41	44	93.2% 🟡
…/DependencyInjection/InternalServiceCollectionExtensions.cs	3	3	100.0% 🟢
…/src/Types/Execution/Processing/OperationContext.Execution.cs	6	6	100.0% 🟢
…/src/Types/Execution/Processing/Tasks/BatchResolverTask.cs	16	16	100.0% 🟢
…/Core/src/Types/Execution/Processing/Tasks/DeferTask.cs	1	1	100.0% 🟢
…/src/Types/Execution/Processing/Tasks/ResolverTask.Execute.cs	2	2	100.0% 🟢
…/src/Types/Execution/Processing/Tasks/ResolverTask.Pooling.cs	14	14	100.0% 🟢

Uncovered changed lines (JSON)

{
  "sha": "c9d2f8034273fd304f654c55159369dbc297327e",
  "files": [
    { "path": "src/HotChocolate/Core/src/Types/Execution/Processing/OperationContext.Pooling.cs", "ranges": [[124, 126]] }
  ]
}

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Project coverage: 59.1% (312353/528635 lines)