test: add test_stop_before_starting_compaction_manager

main.cc

@@ -1297,6 +1297,10 @@ To start the scylla server proper, simply invoke as: scylla server (or just scyl
             auto stop_cm = defer_verbose_shutdown("compaction_manager", [&cm] {
                cm.stop().get();
             });
+
+            utils::get_local_injector().inject("stop_before_starting_compaction_manager",
+                    [] { throw std::runtime_error("injected failure before starting compaction_manager"); });
+
             cm.invoke_on_all(&compaction::compaction_manager::start, std::ref(*cfg), only_on_shard0(&*disk_space_monitor_shard0)).get();
 
             auto compaction_throughput_update = io_throughput_updater("compaction", dbcfg.compaction_scheduling_group, cfg->compaction_throughput_mb_per_sec);

test/cluster/test_stop_before_starting_compaction_manager.py

@@ -0,0 +1,20 @@
+#
+# Copyright (C) 2026-present ScyllaDB
+#
+# SPDX-License-Identifier: LicenseRef-ScyllaDB-Source-Available-1.1
+#
+
+import pytest
+from test.pylib.manager_client import ManagerClient
+
+
+@pytest.mark.skip_mode(mode='release', reason='error injections are not supported in release mode')
+async def test_stop_before_starting_compaction_manager(manager: ManagerClient) -> None:
+    """Test that Scylla doesn't crash when stopped during boot after constructing compaction manager (and thus
+    registering its task_manager module), but before enabling it (calling compaction_manager::enable()).
+
+    Reproducer for SCYLLADB-2106.
+    """
+    await manager.server_add(
+            config={"error_injections_at_startup": ["stop_before_starting_compaction_manager"]},
+            expected_error="injected failure before starting compaction_manager")