Extend agent tests for cloud fleet features and erasure lanes.

Cover fleet torrent DHT fetch, cloud map/venue/meta IMDS mocks, S3 shard fetch order, zero-server policy polling, self-surgery reorder, contingency skip paths, epidemiology fix guards, and ssm_document deploy lane.

agent/deploy/cloud_instance_meta_test.go

@@ -27,3 +27,15 @@ func TestReadEC2InstanceMetaNonAWSFallback(t *testing.T) {
 		t.Fatal("expected empty meta on non-AWS fallback")
 	}
 }
+
+func TestReadEC2InstanceMetaRegionFromAZ(t *testing.T) {
+	prev := ec2IMDSReadMeta
+	t.Cleanup(func() { ec2IMDSReadMeta = prev })
+	ec2IMDSReadMeta = func(ctx context.Context) (CloudInstanceMeta, error) {
+		return CloudInstanceMeta{Region: "us-west-2", SubnetID: "subnet-123"}, nil
+	}
+	meta := ReadEC2InstanceMeta()
+	if meta.Region != "us-west-2" || meta.SubnetID != "subnet-123" {
+		t.Fatalf("meta=%+v", meta)
+	}
+}