Remove forced DispatchConsistency.Isolated for outbox operations

[Copilot]

Outbox was forcing DispatchConsistency.Isolated on all operations, preventing transports from batching messages. This was redundant - the outbox already enforces TransportTransactionMode.ReceiveOnly, which by definition prevents enlistment in receive transactions.

Changes

• Removed ForceBatchDispatchToBeIsolatedBehavior - Deleted behavior class and its pipeline registration
• Updated TransportReceiveToPhysicalMessageConnector - Changed outbox operation dispatch consistency from Isolated to Default
• Updated Outbox.cs comments - Clarified that ReceiveOnly mode already provides isolation guarantees

Impact

Transports supporting batching (Azure Service Bus, Amazon SQS) can now batch outbox operations, reducing latency and message operation costs.

// Before: Each operation dispatched individually
operation.RequiredDispatchConsistency = DispatchConsistency.Isolated;

// After: Transport decides batching strategy
operation.RequiredDispatchConsistency = DispatchConsistency.Default;

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• f.feedz.io
  • Triggering command: /usr/bin/dotnet dotnet build src/NServiceBus.Core/NServiceBus.Core.csproj --no-restore (dns block)
  • Triggering command: /usr/bin/dotnet dotnet build --no-restore -c Release (dns block)
  • Triggering command: /usr/bin/dotnet dotnet restore src/NServiceBus.Core.Tests/NServiceBus.Core.Tests.csproj (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

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This section details on the original issue you should resolve

<issue_title>Outbox prevents transports from batching outgoing messages</issue_title>
<issue_description>When outbox is enabled, all outgoing messages are forced to use DispatchConsistency.Isolated. This causes transports that support batching, at the time of writing, Azure Service Bus and Amazon SQS, not to use batching but rather send messages one by one. This leads to increased latency and higher costs since the number of message operations increases.

This behavior should not be needed since the outbox will force the transport transaction mode to be ReceiveOnly, which by definition prevents outgoing messages from being enlisted in the receive transaction.

Expected behavior

Dispatch consistency NOT changed on outgoing messages when the outbox is enabled.

Actual behavior

Dispatch consistency changed to DispatchConsistency.Isolated on outgoing messages when the outbox is enabled.

Versions

All supported versions.

Steps to reproduce

Enable the outbox, send more than one message using either Azure ServiceBus or Amazon SQS. Notice that batching is not used.

Relevant log output

Additional Information

Workarounds

Possible solutions

Additional information

</issue_description>

<agent_instructions>fix this bug and add proper tests and acceptance test following the conventions already use in the code. Ping @andreasohlund and me as a reviewer when done.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@andreasohlund We have reviewed this bug and added it to our bug fix queue. However, there is no ETA for when we will get to this bug as it may be prioritized behind other, more urgent, bugs. We will update this issue when it has a team assigned and work begins. @andreasohlund @bbrandt it has always existed

• Fixes Outbox prevents transports from batching outgoing messages #7509

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[danielmarbach]

@copilot try again

[andreasohlund]

How do we deal with users that was "relying" on this behavior like. https://discuss.particular.net/t/azure-service-bus-large-number-of-commands-outbox/4483

Do we need to make this opt-in for sometime?

[bbrandt]

How do we deal with users that was "relying" on this behavior like. https://discuss.particular.net/t/azure-service-bus-large-number-of-commands-outbox/4483

Do we need to make this opt-in for sometime?

Maybe we'd want to allow tuning of the message batch size when using outbox? When sending messages with outbox we can prioritize performance since we are not batching for reasons of transactional consistency, maybe?