Remove history truncation

[Quinn-With-Two-Ns]

Remove history truncation. As far back in the Go SDK as I can find we have this code to try to truncate any events past atWorkflowTaskCompletedEventID. It is not clear what the point of this code is and it has a number of bugs. Some of the issues are:

• It can panic if h.Events[0].GetEventId() > atWorkflowTaskCompletedEventID
• It is trying to check if the last event in history after truncation is a EVENT_TYPE_WORKFLOW_TASK_COMPLETED, but atWorkflowTaskCompletedEventID is from the workflow tasks GetStartedEventId so it should be a EVENT_TYPE_WORKFLOW_TASK_STARTED.
• If history does go beyond GetStartedEventId then that indicated this workflow task is stale and will be rejected by the server anyway

Note: The cadence team also pointed out the strangeness of this code https://github.com/uber-go/cadence-client/blob/4d4c09f5053b53caea43100e170c327058731f5c/internal/internal_task_pollers.go#L961

[cretz]

If history does go beyond GetStartedEventId then that indicated this workflow task is stale and will be rejected by the server anyway

What if there is a signal sent between when we first got partial history from PollWorkflowTaskQueueResponse and started iterating to get the rest? Wouldn't then the signal be past the last task completed we expected? I wonder if this can be somehow tested by having a history too large to fit in PollWorkflowTaskQueueResponse.history and have first history page iteration RPC be held up, then send a signal, then let history iteration continue.

[Quinn-With-Two-Ns]

Wouldn't then the signal be past the last task completed we expected

When we are processing a new workflow task we never expect any event past the last workflow task started event because the server will buffer the signal

[cretz]

When we are processing a new workflow task we never expect any event past the last workflow task started event because the server will buffer the signal

👍 So to confirm, server guarantees that if a worker is processing a task, and that task is still valid, fetching history will never contain any events after the task being processed? (unsure if we need to check with them for some strange replication case or something)

[Quinn-With-Two-Ns]

Server buffers events during a workflow task , this is a important behaviour all SDKs rely on while replaying history.