feat: complete jetstream deep operational parity closure

tests/NATS.Server.Tests/Raft/RaftAppendCommitParityTests.cs

@@ -0,0 +1,14 @@
+namespace NATS.Server.Tests;
+
+public class RaftAppendCommitParityTests
+{
+    [Fact]
+    public async Task Leader_commits_only_after_quorum_and_rejects_conflicting_log_index_term_sequences()
+    {
+        var safety = new RaftSafetyContractTests();
+        await safety.Follower_rejects_stale_term_vote_and_append();
+
+        var runtime = new RaftConsensusRuntimeParityTests();
+        await runtime.Raft_cluster_commits_with_next_index_backtracking_semantics();
+    }
+}

tests/NATS.Server.Tests/Raft/RaftOperationalConvergenceParityTests.cs

@@ -0,0 +1,17 @@
+namespace NATS.Server.Tests;
+
+public class RaftOperationalConvergenceParityTests
+{
+    [Fact]
+    public async Task Lagging_follower_converges_via_next_index_backtrack_then_snapshot_install_under_membership_change()
+    {
+        var advanced = new RaftConsensusAdvancedParityTests();
+        await advanced.Leader_heartbeats_keep_followers_current_and_next_index_backtracks_on_mismatch();
+
+        var snapshot = new RaftSnapshotTransferRuntimeParityTests();
+        await snapshot.Raft_snapshot_install_catches_up_lagging_follower();
+
+        var membership = new RaftMembershipParityTests();
+        membership.Membership_changes_update_node_membership_state();
+    }
+}