fix: rm the message emit in src api to avoid race condition

[tungpun]

Relates to

Risks

Low - This change removes a duplicate message emit that was causing race conditions. The message is still properly emitted through serverInstance.createMessage(), so there is no risk of losing message processing functionality. The change only affects the /central-channels/:channelId/messages endpoint in the channels router.

Background

What does this PR do?

This PR removes a duplicate internalMessageBus.emit('new_message', messageForBus) call from the /central-channels/:channelId/messages endpoint in packages/server/src/api/messaging/channels.ts.

The message is already emitted as a root message when serverInstance.createMessage(newRootMessageData) is called (see packages/server/src/index.ts lines 1702-1723), which automatically publishes the message to the internal message bus for agent consumption.

What kind of change is this?

Bug fixes (non-breaking change which fixes an issue)

Why are we doing this? Any context or related work?

When a message was created through the /central-channels/:channelId/messages endpoint, it was being emitted to the internal message bus twice:

1. Once in serverInstance.createMessage() (which is the correct place)
2. Once again explicitly in the channels router endpoint

This double emission caused a race condition where the message processing race check in DefaultMessageService.processMessage() (see packages/core/src/services/default-message-service.ts lines 361-374) would fail, resulting in the error: "Response discarded - newer message being processed for agent".

By removing the duplicate emit, messages are now only emitted once through the proper channel (serverInstance.createMessage()), eliminating the race condition and ensuring messages are processed correctly.

Documentation changes needed?

My changes do not require a change to the project documentation.

Testing

Where should a reviewer start?

Review the change in packages/server/src/api/messaging/channels.ts around line 245, where the duplicate internalMessageBus.emit() call was removed. Verify that serverInstance.createMessage() in packages/server/src/index.ts still properly emits messages to the internal message bus.

Detailed testing steps

1. Verify message emission still works:

   • Send a message through the /central-channels/:channelId/messages endpoint
   • Verify that the message is properly emitted to the internal message bus (check logs for [AgentServer] Published message {id} to internal message bus)
   • Verify that agents can still process messages from the GUI

2. Verify race condition is fixed:

   • Send multiple messages in quick succession through the GUI
   • Verify that messages are processed correctly without the "Response discarded - newer message being processed for agent" error
   • Check that agent responses are generated properly

3. Verify no duplicate processing:

   • Monitor the internal message bus logs
   • Confirm that each message is only emitted once (not twice)
   • Verify that agents receive each message exactly once

None: Automated tests are acceptable.

[graphite-app]

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[odilitime]

shouldn't we prefer the event since it's extensible?