diff --git a/codex-rs/core-plugins/src/executor_runtime.rs b/codex-rs/core-plugins/src/executor_runtime.rs
index 5c6becf997..0f7e7a5e8e 100644
--- a/codex-rs/core-plugins/src/executor_runtime.rs
+++ b/codex-rs/core-plugins/src/executor_runtime.rs
@@ -17,7 +17,7 @@ use crate::ResolvedExecutorPlugin;
 
 const DEFAULT_MCP_CONFIG_FILE: &str = ".mcp.json";
 
-/// MCP and connector declarations read from one exact executor binding.
+/// MCP and connector declarations read from one stable executor capability root.
 #[derive(Clone, Debug)]
 pub struct ExecutorPluginRuntime {
     plugin: ResolvedPlugin,
@@ -26,10 +26,8 @@ pub struct ExecutorPluginRuntime {
 }
 
 impl ExecutorPluginRuntime {
-    /// Reads both runtime declaration files through the root's pinned filesystem.
-    ///
-    /// `Ok(None)` is intentionally not cacheable: the plugin manifest may appear
-    /// once a deferred executor finishes starting.
+    /// Reads both runtime declaration files through the root's current ready filesystem.
+    /// `Ok(None)` means the stable root is not a plugin and may be cached by the caller.
     pub async fn project(root: &ResolvedSelectedCapabilityRoot) -> anyhow::Result<Option<Self>> {
         let Some(plugin) = ExecutorPluginProvider::resolve_pinned(root).await? else {
             return Ok(None);
diff --git a/codex-rs/core/src/session/mcp_projection.rs b/codex-rs/core/src/session/mcp_projection.rs
index 143a779816..d1dcf6956d 100644
--- a/codex-rs/core/src/session/mcp_projection.rs
+++ b/codex-rs/core/src/session/mcp_projection.rs
@@ -116,7 +116,7 @@ impl Session {
             .environment_manager()
             .resolve_selected_capability_roots(
                 selected_roots,
-                &environments.captured_environments(),
+                &environments.captured_environment_availability(),
             )
             .await;
         let bindings = selected_bindings(selected_roots, &resolved_roots);
diff --git a/codex-rs/core/src/session/mcp_runtime.rs b/codex-rs/core/src/session/mcp_runtime.rs
index 263bf96dd9..2bec6cb1ae 100644
--- a/codex-rs/core/src/session/mcp_runtime.rs
+++ b/codex-rs/core/src/session/mcp_runtime.rs
@@ -9,7 +9,8 @@ use codex_protocol::capabilities::SelectedCapabilityRoot;
 ///
 /// Selected environment identity and contents are stable. Plugin manifests, MCP declarations, and
 /// app declarations are therefore cached by the complete selected root for the session lifetime.
-/// Missing or failed projections are not cached, so a deferred environment can recover later.
+/// Successful projections and stable non-plugin roots are cached. Failed reads are not cached, so
+/// a transient executor error can recover later.
 ///
 /// A live runtime is a separate cache: it is reusable only for the same ordered selected roots and
 /// the same process-local environment handles. The caller additionally compares the effective MCP
@@ -37,7 +38,7 @@ struct CachedSelectedRuntime {
 
 struct CachedExecutorPluginProjection {
     selected_root: SelectedCapabilityRoot,
-    plugin: ExecutorPluginRuntime,
+    plugin: Option<ExecutorPluginRuntime>,
 }
 
 impl SelectedMcpRuntimeCache {
@@ -73,26 +74,28 @@ impl SelectedMcpRuntimeCache {
         let mut plugins = Vec::new();
         for (selection_order, root) in bindings {
             let selected_root = root.selected_root();
-            if let Some(plugin) = self
+            if let Some(cached) = self
                 .plugin_projections
                 .iter()
                 .find(|cached| &cached.selected_root == selected_root)
-                .map(|cached| cached.plugin.clone())
             {
-                plugins.push((*selection_order, plugin));
+                if let Some(plugin) = &cached.plugin {
+                    plugins.push((*selection_order, plugin.clone()));
+                }
                 continue;
             }
 
             match ExecutorPluginRuntime::project(root).await {
-                Ok(Some(plugin)) => {
+                Ok(plugin) => {
                     self.plugin_projections
                         .push(CachedExecutorPluginProjection {
                             selected_root: selected_root.clone(),
                             plugin: plugin.clone(),
                         });
-                    plugins.push((*selection_order, plugin));
+                    if let Some(plugin) = plugin {
+                        plugins.push((*selection_order, plugin));
+                    }
                 }
-                Ok(None) => {}
                 Err(err) => {
                     tracing::warn!(
                         selected_root = selected_root.id,
diff --git a/codex-rs/core/src/session/session.rs b/codex-rs/core/src/session/session.rs
index 8ab001294a..761f74a07c 100644
--- a/codex-rs/core/src/session/session.rs
+++ b/codex-rs/core/src/session/session.rs
@@ -557,10 +557,14 @@ impl Session {
             config.current_time_reminder.as_ref(),
             external_time_provider,
         )?;
-        let selected_capability_roots = if selected_capability_roots.is_empty() {
-            initial_history.get_selected_capability_roots()
-        } else {
+        let selected_capability_roots = if !selected_capability_roots.is_empty() {
             selected_capability_roots
+        } else if let Some(selected_capability_roots) =
+            thread_extension_init.get::<Vec<SelectedCapabilityRoot>>()
+        {
+            selected_capability_roots.as_ref().clone()
+        } else {
+            initial_history.get_selected_capability_roots()
         };
         let thread_extension_data = codex_extension_api::ExtensionData::new_with_init(
             thread_id.to_string(),