[alexoneill]

Add an optional google.protobuf.Duration per_operation_timeout field to each operation request message in test_proxy.proto (ReadRowRequest, ReadRowsRequest, MutateRowRequest, MutateRowsRequest, CheckAndMutateRowRequest, SampleRowKeysRequest, ReadModifyWriteRowRequest, and ExecuteQueryRequest) so callers can override CreateClientRequest.per_operation_timeout (in both directions) and the client library default timeout on a per-call basis.

• Pass callContext into retryAlgorithm.createFirstAttempt(callContext) in MutateRowsAttemptCallable so per-call RetrySettings overrides on bulkMutationCallable().call(batch, callContext) apply to entry-level retry decisions as well as the parent RetryingFuture.
• Add hasPositiveTimeout and createCallContextWithTimeout in CbtTestProxy, updating updateTimeout to also raise initialRpcTimeoutDuration and maxRpcTimeoutDuration when they were previously clamped equal to oldTotalTimeout.
• Plumb per-operation timeout overrides through mutateRow, bulkMutateRows, readRow, readRows, sampleRowKeys, checkAndMutateRow, readModifyWriteRow, and executeQuery.
• Add unit tests in CbtTestProxyTest and MutateRowsAttemptCallableTest covering shorter and longer per-operation timeout overrides.

[gemini-code-assist]

Code Review

This pull request introduces per-operation timeout overrides for various Bigtable operations in the test proxy, updating CbtTestProxy to apply these timeouts and extending test_proxy.proto with per_operation_timeout fields. It also includes comprehensive tests verifying that these overrides correctly supersede client-level timeouts, and updates MutateRowsAttemptCallable to pass the call context on the first attempt. Feedback on the changes highlights a potential NullPointerException in CbtTestProxy.java if previousContext is null when calling detach, which should be guarded to prevent masking other exceptions.

[gemini-code-assist]

If cancellableContext is initialized but previousContext remains null (for example, if an exception occurs or the thread is interrupted before attach() completes), calling cancellableContext.detach(previousContext) will throw a NullPointerException because Context.detach does not accept null. This NPE would mask the original exception.

To prevent this, guard the detach call by checking if previousContext is not null.

      if (previousContext != null) {
        cancellableContext.detach(previousContext);
      }
      if (cancellableContext != null) {
        cancellableContext.close();
      }