test(replication): pin SSE replication contracts (#4883)

.github/workflows/e2e-replication-nightly.yml

@@ -15,12 +15,14 @@
 # Nightly full replication e2e lane (backlog#1147 repl-1, deps: ci-4).
 #
 # The per-PR gate (ci.yml `e2e-tests` job, `--profile e2e-smoke`) runs the 20
-# FAST replication tests. This scheduled lane runs the remaining 24
+# FAST replication tests. This scheduled lane runs the remaining 27
 # heavier replication e2e tests that are unfit for a per-PR gate:
 #
 #   * 2 remote-target TLS validation tests.
-#   * 9 bucket-replication data-plane tests (PUT/delete + poll for convergence;
-#     two replicate over HTTPS).
+#   * 12 bucket-replication data-plane/helper tests (PUT/delete + poll for
+#     convergence; two replicate over HTTPS, two pin active SSE failure
+#     contracts, and one guards event/history observers). The SSE-S3 contract
+#     remains ignored under backlog#1291.
 #   * 11 `_real_dual_node` site-replication tests (each spawns TWO rustfs
 #     servers and drives the cross-process site-replication control plane).
 #   * 1 `_real_three_node` site-replication test.
@@ -30,7 +32,7 @@
 # .config/nextest.toml — the single wiring mechanism (repl-1 / ci-4). Do NOT
 # add ad-hoc cargo-test steps here; change the filterset instead.
 #
-# Explicit division of labor: these 24 tests run ONLY here, never double-run
+# Explicit division of labor: these 27 tests run ONLY here, never double-run
 # in ci-5's future e2e-full merge gate. TODO(ci-7): once the ci domain's
 # consolidated scheduled e2e workflow exists, fold this interim repl-owned lane
 # into it rather than growing a second scheduled entrypoint.