Acquire and cache opt-in executor capability inventories via V2 (#53736)

## What changed

- Add the disabled-by-default `executor_capability_discovery_v2` feature to acquire `capabilities/discoverV2` inventories from supporting remote executors using each selected environment's working directory and sandbox.
- Share snapshots with MCP and world-state contributors and skill providers without activating discovered plugins or publishing discovered skills to the model.
- Cache inventories by environment instance, executor session, working directory, and sandbox. Coalesce concurrent requests, refresh the cache at turn start, retry transient failures, and refresh MCP projections after recovery.
- Resolve the system skills root in the executor and pass it explicitly to capability location discovery.

## Testing

Add coverage for feature gating, unsupported executors, inert inventories, cache reuse and eviction, turn refreshes, failure recovery, executor replacement, and system skill locations.

GitOrigin-RevId: 1bdca28fa7f17622b27e2713ab3dcc0c13426889

codex-rs/ext/extension-api/src/contributors/mcp.rs

@@ -1,5 +1,6 @@
 use codex_config::McpServerConfig;
 use codex_exec_server_protocol::ExecutorCapabilityDiscoverySnapshot;
+use codex_exec_server_protocol::ExecutorCapabilityDiscoveryV2Snapshot;
 use codex_protocol::capabilities::SelectedCapabilityRoot;
 use codex_protocol::protocol::SessionSource;
 use codex_protocol::protocol::TurnEnvironmentSelection;
@@ -32,6 +33,8 @@ pub struct McpServerContributionContext<'a, C> {
     ready_selected_capability_roots: Option<&'a [SelectedCapabilityRoot]>,
     /// Executor-materialized capability files shared by all consumers in this exact step.
     executor_capability_discovery: Option<&'a ExecutorCapabilityDiscoverySnapshot>,
+    /// V2 inventories supplied by the host for this contribution.
+    executor_capability_discovery_v2: Option<&'a [ExecutorCapabilityDiscoveryV2Snapshot]>,
 }
 
 impl<C> Clone for McpServerContributionContext<'_, C> {
@@ -55,6 +58,7 @@ impl<'a, C> McpServerContributionContext<'a, C> {
             selected_environments: None,
             ready_selected_capability_roots: None,
             executor_capability_discovery: None,
+            executor_capability_discovery_v2: None,
         }
     }
 
@@ -66,6 +70,7 @@ impl<'a, C> McpServerContributionContext<'a, C> {
         originator: &'a str,
         ready_selected_capability_roots: &'a [SelectedCapabilityRoot],
         executor_capability_discovery: Option<&'a ExecutorCapabilityDiscoverySnapshot>,
+        executor_capability_discovery_v2: Option<&'a [ExecutorCapabilityDiscoveryV2Snapshot]>,
     ) -> Self {
         Self {
             config,
@@ -77,6 +82,7 @@ impl<'a, C> McpServerContributionContext<'a, C> {
             selected_environments: None,
             ready_selected_capability_roots: Some(ready_selected_capability_roots),
             executor_capability_discovery,
+            executor_capability_discovery_v2,
         }
     }
 
@@ -145,6 +151,13 @@ impl<'a, C> McpServerContributionContext<'a, C> {
         self.ready_selected_capability_roots
     }
 
+    /// Returns the V2 inventories supplied by the host, when available.
+    pub fn executor_capability_discovery_v2(
+        &self,
+    ) -> Option<&'a [ExecutorCapabilityDiscoveryV2Snapshot]> {
+        self.executor_capability_discovery_v2
+    }
+
     /// Returns the executor-materialized capability files for this model step, when enabled.
     pub fn executor_capability_discovery(&self) -> Option<&'a ExecutorCapabilityDiscoverySnapshot> {
         self.executor_capability_discovery

codex-rs/ext/extension-api/src/contributors/world_state.rs

@@ -1,6 +1,7 @@
 use std::sync::Arc;
 
 use codex_exec_server_protocol::ExecutorCapabilityDiscoverySnapshot;
+use codex_exec_server_protocol::ExecutorCapabilityDiscoveryV2Snapshot;
 use codex_protocol::ThreadId;
 use codex_protocol::capabilities::SelectedCapabilityRoot;
 use codex_protocol::openai_models::ModelInfo;
@@ -21,6 +22,8 @@ pub struct WorldStateContributionInput<'a> {
     pub ready_selected_capability_roots: &'a [SelectedCapabilityRoot],
     /// Executor-materialized capability files shared by all consumers in this exact step.
     pub executor_capability_discovery: Option<&'a ExecutorCapabilityDiscoverySnapshot>,
+    /// Opted-in executor inventories captured for this exact step.
+    pub executor_capability_discovery_v2: Option<&'a [ExecutorCapabilityDiscoveryV2Snapshot]>,
     /// Metrics bound to the captured model for this sampling step.
     pub extension_metrics: Option<Arc<dyn ExtensionMetrics>>,
     pub session_store: &'a ExtensionData,