fix: address PR reviewer findings - remove substring false-positive and add error case tests

- Remove substring check in _force_ecs_deployment that could match wrong
  services (e.g. my-app:5 matching my-app:50). Use family-name comparison only.
- Add unit tests for ContainerName mismatch error handling in both
  app_builder and packageable_resources.
- Clean up unused imports in test file.

Author: singledigit

samcli/lib/sync/flows/ecs_container_sync_flow.py

@@ -184,13 +184,11 @@ def _force_ecs_deployment(self) -> None:
                     service_name = parts[-1]
 
                     svc_response = ecs_client.describe_services(cluster=cluster, services=[service_name])
+                    my_family = physical_id.rsplit("/", 1)[-1].split(":", 1)[0]
                     for svc in svc_response.get("services", []):
                         svc_task_def = svc.get("taskDefinition", "")
-                        # Check if this service references our task definition family
-                        if physical_id in svc_task_def or (
-                            svc_task_def.rsplit("/", 1)[-1].split(":", 1)[0]
-                            == physical_id.rsplit("/", 1)[-1].split(":", 1)[0]
-                        ):
+                        svc_family = svc_task_def.rsplit("/", 1)[-1].split(":", 1)[0]
+                        if svc_family and svc_family == my_family:
                             ecs_client.update_service(
                                 cluster=cluster,
                                 service=service_name,

tests/unit/lib/build_module/test_container_build_integration.py

@@ -1,8 +1,7 @@
 """Tests for ECS/AgentCore container build integration across modules"""
 
 from unittest import TestCase
-from unittest.mock import MagicMock, patch, Mock
-from copy import deepcopy
+from unittest.mock import MagicMock, patch
 
 from samcli.lib.build.app_builder import ApplicationBuilder
 from samcli.lib.build.build_graph import ContainerBuildDefinition
@@ -184,7 +183,7 @@ def test_includes_container_services(
         mock_manager.get_repository_mapping.return_value = {"MyFunction": "uri1", "MyAgent": "uri2"}
         mock_manager_cls.return_value = mock_manager
 
-        result = sync_ecr_stack("template.yaml", "stack", "us-east-1", "bucket", "prefix", {})
+        sync_ecr_stack("template.yaml", "stack", "us-east-1", "bucket", "prefix", {})
 
         # Verify both function and container service were passed
         call_args = mock_manager.set_functions.call_args[0]
@@ -257,3 +256,41 @@ def test_sync_skips_when_no_image(self):
         flow._physical_id_mapping = {}
         # Should not raise
         flow.sync()
+
+
+class TestContainerNameErrorHandling(TestCase):
+    def test_update_built_resource_raises_on_container_name_mismatch(self):
+        from samcli.lib.build.exceptions import DockerBuildFailed
+
+        properties = {
+            "ContainerDefinitions": [
+                {"Name": "sidecar", "Image": "sidecar:latest"},
+                {"Name": "web", "Image": "placeholder"},
+            ]
+        }
+        metadata = {"ContainerName": "typo"}
+        with self.assertRaises(DockerBuildFailed):
+            ApplicationBuilder._update_built_resource(
+                "myimage:latest", properties, AWS_ECS_TASK_DEFINITION, "/path", metadata
+            )
+
+    def test_get_target_index_raises_on_container_name_mismatch(self):
+        from samcli.commands.package import exceptions
+
+        exporter = ECSTaskDefinitionImageResource.__new__(ECSTaskDefinitionImageResource)
+        exporter.resource_metadata = {"ContainerName": "typo"}
+        container_defs = [{"Name": "web"}, {"Name": "sidecar"}]
+        with self.assertRaises(exceptions.ExportFailedError):
+            exporter._get_target_index(container_defs)
+
+    def test_get_target_index_returns_match(self):
+        exporter = ECSTaskDefinitionImageResource.__new__(ECSTaskDefinitionImageResource)
+        exporter.resource_metadata = {"ContainerName": "web"}
+        container_defs = [{"Name": "sidecar"}, {"Name": "web"}]
+        self.assertEqual(exporter._get_target_index(container_defs), 1)
+
+    def test_get_target_index_defaults_to_zero_without_name(self):
+        exporter = ECSTaskDefinitionImageResource.__new__(ECSTaskDefinitionImageResource)
+        exporter.resource_metadata = {}
+        container_defs = [{"Name": "web"}]
+        self.assertEqual(exporter._get_target_index(container_defs), 0)