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/core-plugins/src/provider.rs

@@ -1,19 +1,22 @@
-//! Plugin catalog listing interface and the MCP context used to request snapshots.
+//! Plugin catalog listing interface and source inputs used to request snapshots.
 
 use crate::ExecutorPluginProviderError;
 use crate::PluginCatalog;
+use codex_exec_server::ExecutorCapabilityDiscoveryV2Snapshot;
 use codex_mcp::McpResourceClient;
 use std::future::Future;
 use std::pin::Pin;
 use std::sync::Arc;
 use thiserror::Error;
 
-/// Turn identifiers and MCP client used to request one catalog snapshot.
+/// Identifiers, MCP client, and executor inventories used to request one catalog snapshot.
 #[derive(Clone, Debug)]
 pub struct PluginListQuery {
     pub thread_id: String,
     pub turn_id: String,
     pub mcp_resources: Option<Arc<McpResourceClient>>,
+    /// Already-acquired V2 inventories; empty for cloud listing.
+    pub snapshots: Vec<ExecutorCapabilityDiscoveryV2Snapshot>,
 }
 
 /// Failure to list plugin metadata.