The local cluster member is not a leader - Change exception type from InvalidOperationException to a more specific NotALeaderException

[pwhsoft]

Currently, when attempting to perform a Raft operation on a non-leader node, the following exception is thrown:

System.InvalidOperationException: The local cluster member is not a leader
 ---> System.OperationCanceledException: The operation was canceled.

Problem:
InvalidOperationException is too generic for this scenario and makes it difficult to distinguish between general invalid operations and leadership-related errors.

Suggestion:
Introduce a more specific exception type (e.g., NotALeaderException, LeaderUnavailableException, or similar) to clearly signal that the operation failed because the current node is not the Raft cluster leader.

Rationale:

Improves error handling for client applications.

Makes it easier to implement leader redirection or retry logic.

Better reflects the semantics of Raft operations.

Stack trace (for reference):

System.InvalidOperationException: The local cluster member is not a leader
 ---> System.OperationCanceledException: The operation was canceled.
   at DotNext.Result`1.get_Value() in /_/src/DotNext/Result.cs:line 177
   ...
   at DotNext.Net.Cluster.Consensus.Raft.RaftCluster`1.ReplicateAsync[TEntry](TEntry entry, CancellationToken token)

[sakno]

Well... it's a subject for discussion. The description for InvalidOperationException says the following:

The exception that is thrown when a method call is invalid for the object's current state

Which is true for ReplicateAsync, because you're trying to call this method on the node that is not a leader. The exception is described in XML docs for the method and it's a part of the behavioral contract. Maybe, I could introduce the exception derived from InvalidOperationException to keep backward compatibility, but the name for this exception is a challenge 😃

[sakno]

I have two candidates:

• NotLeaderException
• InvalidLeaderOperationException