diff --git a/codex-rs/core/src/agent/control/spawn.rs b/codex-rs/core/src/agent/control/spawn.rs
index 6919d8c627..c4c40577ca 100644
--- a/codex-rs/core/src/agent/control/spawn.rs
+++ b/codex-rs/core/src/agent/control/spawn.rs
@@ -1,5 +1,6 @@
 use super::residency::is_v2_resident_session_source;
 use super::*;
+use codex_extension_api::ExtensionDataInit;
 
 const AGENT_NAMES: &str = include_str!("../agent_names.txt");
 
@@ -433,6 +434,16 @@ impl AgentControl {
                 ))
             })?;
 
+        let selected_capability_roots = parent_history
+            .items
+            .iter()
+            .find_map(|item| {
+                let RolloutItem::SessionMeta(meta_line) = item else {
+                    return None;
+                };
+                Some(meta_line.meta.selected_capability_roots.clone())
+            })
+            .unwrap_or_default();
         let mut forked_rollout_items = parent_history.items;
         if let SpawnAgentForkMode::LastNTurns(last_n_turns) = fork_mode {
             forked_rollout_items =
@@ -504,6 +515,8 @@ impl AgentControl {
         {
             forked_rollout_items.push(RolloutItem::ResponseItem(subagent_usage_hint_message));
         }
+        let mut thread_extension_init = ExtensionDataInit::new();
+        thread_extension_init.insert(selected_capability_roots);
 
         state
             .fork_thread_with_source(
@@ -517,6 +530,7 @@ impl AgentControl {
                 inherited_environments,
                 inherited_exec_policy,
                 options.environments.clone(),
+                thread_extension_init,
             )
             .await
     }
diff --git a/codex-rs/core/src/agent/control_tests.rs b/codex-rs/core/src/agent/control_tests.rs
index e00a8624f4..de8754ad92 100644
--- a/codex-rs/core/src/agent/control_tests.rs
+++ b/codex-rs/core/src/agent/control_tests.rs
@@ -17,6 +17,8 @@ use codex_features::Feature;
 use codex_login::AuthManager;
 use codex_login::CodexAuth;
 use codex_protocol::AgentPath;
+use codex_protocol::capabilities::CapabilityRootLocation;
+use codex_protocol::capabilities::SelectedCapabilityRoot;
 use codex_protocol::config_types::ModeKind;
 use codex_protocol::models::ContentItem;
 use codex_protocol::models::MessagePhase;
@@ -38,6 +40,7 @@ use codex_thread_store::InMemoryThreadStore;
 use codex_thread_store::LocalThreadStore;
 use codex_thread_store::LocalThreadStoreConfig;
 use codex_thread_store::ThreadStore;
+use codex_utils_path_uri::PathUri;
 use pretty_assertions::assert_eq;
 use tempfile::TempDir;
 use tokio::time::Duration;
@@ -1446,7 +1449,33 @@ async fn spawn_agent_fork_last_n_turns_keeps_only_recent_turns() {
 #[tokio::test]
 async fn spawn_agent_fork_last_n_turns_drops_parent_startup_prefix_when_under_limit() {
     let harness = AgentControlHarness::new().await;
-    let (parent_thread_id, parent_thread) = harness.start_thread().await;
+    let selected_capability_roots = vec![SelectedCapabilityRoot {
+        id: "demo@1".to_string(),
+        location: CapabilityRootLocation::Environment {
+            environment_id: "build".to_string(),
+            path: PathUri::parse("file:///plugins/demo").expect("plugin root URI"),
+        },
+    }];
+    let mut thread_extension_init = ExtensionDataInit::new();
+    thread_extension_init.insert(selected_capability_roots.clone());
+    let parent = harness
+        .manager
+        .start_thread_with_options(StartThreadOptions {
+            config: harness.config.clone(),
+            initial_history: InitialHistory::New,
+            session_source: None,
+            thread_source: None,
+            dynamic_tools: Vec::new(),
+            metrics_service_name: None,
+            parent_trace: None,
+            environments: Vec::new(),
+            thread_extension_init,
+            supports_openai_form_elicitation: false,
+        })
+        .await
+        .expect("start parent thread");
+    let parent_thread_id = parent.thread_id;
+    let parent_thread = parent.thread;
     let startup_turn_context = parent_thread.codex.session.new_default_turn().await;
     parent_thread
         .codex
@@ -1525,6 +1554,14 @@ async fn spawn_agent_fork_last_n_turns_drops_parent_startup_prefix_when_under_li
         !history_contains_text(history.raw_items(), "parent startup developer context"),
         "bounded fork should drop parent startup context even when fewer turns exist than requested"
     );
+    assert_eq!(
+        &child_thread
+            .codex
+            .session
+            .services
+            .selected_capability_roots,
+        &selected_capability_roots
+    );
     assert!(
         child_thread
             .codex
diff --git a/codex-rs/core/src/thread_manager.rs b/codex-rs/core/src/thread_manager.rs
index 98e13c5d67..b2add06024 100644
--- a/codex-rs/core/src/thread_manager.rs
+++ b/codex-rs/core/src/thread_manager.rs
@@ -1402,6 +1402,7 @@ impl ThreadManagerState {
         inherited_environments: Option<TurnEnvironmentSnapshot>,
         inherited_exec_policy: Option<Arc<crate::exec_policy::ExecPolicyManager>>,
         environments: Option<Vec<TurnEnvironmentSelection>>,
+        thread_extension_init: ExtensionDataInit,
     ) -> CodexResult<NewThread> {
         let environments = environments.unwrap_or_else(|| {
             default_thread_environment_selections(self.environment_manager.as_ref(), &config.cwd)
@@ -1421,7 +1422,7 @@ impl ThreadManagerState {
             inherited_exec_policy,
             /*parent_trace*/ None,
             environments,
-            /*thread_extension_init*/ ExtensionDataInit::default(),
+            thread_extension_init,
             /*supports_openai_form_elicitation*/ false,
             /*user_shell_override*/ None,
         ))