fix: default effective canister id for PocketIC

e2e/tests-dfx/start.bash

@@ -29,6 +29,18 @@ teardown() {
   dfx_stop
 }
 
+@test "start and stop with specified canister id" {
+  dfx_start
+
+  dfx_new hello
+  dfx deploy hello_backend --specified-id gt2iw-kiaaa-aaad7-qaaaa-cai
+
+  dfx_stop
+
+  dfx_start
+  dfx_stop
+}
+
 @test "start and stop with different options" {
   [[ "$USE_POCKETIC" ]] && skip "skipped for pocketic: clean required"
   dfx_start --artificial-delay 101

src/dfx/src/actors/pocketic.rs

@@ -385,25 +385,12 @@ async fn initialize_pocketic(
             instance_id,
             topology,
         } => {
-            let subnets = match replica_config.subnet_type {
-                ReplicaSubnetType::Application => topology.get_app_subnets(),
-                ReplicaSubnetType::System => topology.get_system_subnets(),
-                ReplicaSubnetType::VerifiedApplication => topology.get_verified_app_subnets(),
-            };
-            if subnets.len() != 1 {
-                return Err(anyhow!("Internal error: PocketIC topology contains multiple subnets of the same subnet kind."));
-            }
-            let subnet_id = subnets[0];
-            let subnet_config = topology.subnet_configs.get(&subnet_id).ok_or(anyhow!(
-                "Internal error: subnet id {} not found in PocketIC topology",
-                subnet_id
-            ))?;
-            let effective_canister_id =
-                Principal::from_slice(&subnet_config.canister_ranges[0].start.canister_id);
+            let default_effective_canister_id: Principal =
+                topology.default_effective_canister_id.into();
             let effective_config = CachedConfig::pocketic(
                 replica_config,
                 replica_rev().into(),
-                Some(effective_canister_id),
+                Some(default_effective_canister_id),
             );
             save_json_file(effective_config_path, &effective_config)?;
             instance_id