feat(raft-sim-conformance): drop/duplicate/reorder adversarial scenario (task 5.3)

src/lib/raft/raft.h

@@ -1013,6 +1013,30 @@ int raft_sim_scenario_partition_heal(raft_sim_cluster_t *c, int n, uint64_t seed
  */
 int raft_sim_scenario_restart_churn(raft_sim_cluster_t *c, int n, uint64_t seed);
 
+/*
+ * raft_sim_scenario_drop_dup_reorder: drop/duplicate/reorder scenario (raft-sim-
+ * conformance task 5.3; Req 4.3). Initializes the caller's cluster from (n,
+ * election_timeout=2000, seed), then:
+ *   1. drives it to a single leader + replicated entries,
+ *   2. PERTURBS the unified message bag — DROPs some in-flight messages
+ *      (raft_sim_bag_drop), DUPLICATEs some (raft_sim_bag_duplicate, so an
+ *      AppendEntries / vote response is delivered MORE THAN ONCE), and REORDERs
+ *      delivery (raft_sim_bag_pick PRNG order, not FIFO) through the real handlers
+ *      (raft_sim_bag_deliver),
+ *   3. because dropped messages leave followers behind, the leader RETRANSMITs over
+ *      additional replicate rounds until the logs converge (bounded).
+ * raft_sim_check_all is run after EVERY action it applies — DURING perturbation and
+ * after each retransmit — so a violation is caught the moment it appears (Req 4.1). A
+ * duplicated AppendEntries is a no-op (the library's already-have branch): delivering
+ * the same AE twice never grows or corrupts the follower's log. Returns 0 if the
+ * scenario completes with ZERO invariant violations AND every node's log converged to
+ * the leader's tip (idempotent convergence); < 0 (the negated first failing invariant,
+ * matching raft_sim_step) on any violation, after dumping the replayable trace to
+ * stderr. Returns -1 on an invalid node count (n < 3). Drives only via published
+ * library entry points + harness bag primitives — no protocol re-implementation.
+ */
+int raft_sim_scenario_drop_dup_reorder(raft_sim_cluster_t *c, int n, uint64_t seed);
+
 #endif /* XCE_TESTING */
 
 #endif /* RAFT_H */