diff --git a/tests/test_adapter.py b/tests/test_adapter.py
index ffd0bde..a1ee5f4 100644
--- a/tests/test_adapter.py
+++ b/tests/test_adapter.py
@@ -9,7 +9,7 @@ import pytest
 
 sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
 
-from adapters.terraform.adapter import adapt, _tf_value, _ref_expr, _module_name
+from adapters.terraform.adapter import adapt, _tf_value, _ref_expr, _module_name, _child_id
 
 ROOT = Path(__file__).resolve().parent.parent
 
@@ -241,4 +241,93 @@ class TestAdapterEmitsValidTerraform:
             ["terraform", "validate"],
             cwd=str(tmp_path), capture_output=True, text=True
         )
-        assert result.returncode == 0, f"terraform validate failed: {result.stderr}"
\ No newline at end of file
+        assert result.returncode == 0, f"terraform validate failed: {result.stderr}"
+
+
+class TestAdapterDedupMultiResourceL1:
+    """CAP-013 (v1.12, REQ-129): multi-resource L1s (ecs-service, alb) with
+    stack outputs + cross-module refs must dedup to ONE module block named by
+    the composition child id, with all expanded sub-ids rewritten. This is the
+    regression test that locks in the fix — a future refactor that re-breaks
+    the dedup must turn this red."""
+
+    def test_microservice_dedup_names_modules_by_child_id(self, tmp_path):
+        import sys
+        sys.path.insert(0, str(ROOT))
+        from core.contract_resolver import resolve
+        stack = resolve(str(ROOT / "contracts/microservice.yml"))
+        adapt(stack, str(tmp_path))
+        main_tf = (tmp_path / "main.tf").read_text()
+        # The merged modules are named by the child id (alb, service), not the
+        # expanded sub-ids (alb-loadbalancer, service-service, ...).
+        assert 'module "alb" {' in main_tf
+        assert 'module "service" {' in main_tf
+        # Expanded sub-ids must NOT appear as module names.
+        assert 'module "alb-loadbalancer"' not in main_tf
+        assert 'module "alb-targetgroup"' not in main_tf
+        assert 'module "alb-listener"' not in main_tf
+        assert 'module "service-task-definition"' not in main_tf
+        assert 'module "service-service"' not in main_tf
+
+    def test_microservice_dedup_rewrites_stack_outputs(self, tmp_path):
+        """Stack outputs reference the expanded sub-ids; after dedup they
+        must resolve to the child-id module name."""
+        import sys
+        sys.path.insert(0, str(ROOT))
+        from core.contract_resolver import resolve
+        stack = resolve(str(ROOT / "contracts/microservice.yml"))
+        adapt(stack, str(tmp_path))
+        main_tf = (tmp_path / "main.tf").read_text()
+        # service_arn output references service-service -> module.service
+        assert 'output "service_arn" {\n  value = module.service.service_arn' in main_tf
+        # lb_arn output references alb-loadbalancer -> module.alb
+        assert 'output "lb_arn" {\n  value = module.alb.lb_arn' in main_tf
+
+    def test_microservice_dedup_rewrites_cross_module_refs(self, tmp_path):
+        """A ref: input that targets an expanded sub-id (e.g.
+        ref:alb-targetgroup.target_group_arn) must be rewritten to the
+        child-id module (module.alb.target_group_arn)."""
+        import sys
+        sys.path.insert(0, str(ROOT))
+        from core.contract_resolver import resolve
+        stack = resolve(str(ROOT / "contracts/microservice.yml"))
+        adapt(stack, str(tmp_path))
+        main_tf = (tmp_path / "main.tf").read_text()
+        assert "lb_target_group_arn = module.alb.target_group_arn" in main_tf
+        # The un-rewritten expanded form must NOT appear.
+        assert "module.alb-targetgroup" not in main_tf
+        assert "module.service-service" not in main_tf
+
+    def test_microservice_emits_valid_terraform(self, tmp_path):
+        """CAP-013 end-to-end: the microservice (multi-resource L1s) main.tf
+        passes terraform init + validate. This is the real regression — the
+        v1.11 dedup produced 'No module call name' here."""
+        import sys
+        sys.path.insert(0, str(ROOT))
+        from core.contract_resolver import resolve
+        stack = resolve(str(ROOT / "contracts/microservice.yml"))
+        adapt(stack, str(tmp_path))
+        result = subprocess.run(
+            ["terraform", "init", "-backend=false", "-input=false"],
+            cwd=str(tmp_path), capture_output=True, text=True
+        )
+        assert result.returncode == 0, f"terraform init failed: {result.stderr}"
+        result = subprocess.run(
+            ["terraform", "validate"],
+            cwd=str(tmp_path), capture_output=True, text=True
+        )
+        assert result.returncode == 0, f"terraform validate failed (CAP-013 regression): {result.stderr}"
+
+
+class TestChildIdHelper:
+    """Unit tests for _child_id (the common-prefix heuristic)."""
+
+    def test_single_resource_returns_id_verbatim(self):
+        assert _child_id(["cluster"]) == "cluster"
+        assert _child_id(["kms-key"]) == "kms-key"
+
+    def test_multi_resource_returns_common_prefix(self):
+        # ecs-service expands to service-task-definition + service-service
+        assert _child_id(["service-task-definition", "service-service"]) == "service"
+        # alb expands to alb-loadbalancer + alb-targetgroup + alb-listener
+        assert _child_id(["alb-loadbalancer", "alb-targetgroup", "alb-listener"]) == "alb"
\ No newline at end of file