Integrate discovery V2 with step-scoped skill catalogs (#55322)

## What changed

- Build executor skill catalogs from discovery V2 inventories without reopening host paths or falling back to legacy discovery.
- Merge Cloud and executor skills by remote plugin identity and skill name, retaining Cloud metadata and accepted provider read routes. Apply plugin selection and disablement before merging.
- Share a stable catalog across each step's rendering, list/read tools, and explicit and implicit skill invocations.
- Preserve unmatched executor entries when Cloud catalogs are unavailable or partial; only complete Cloud catalogs disable unmatched remote entries.
- Bind discovery caches to captured environments and executor sessions, and refresh MCP when V2 inventories change. Preserve pending invalidations when forced MCP refreshes fail.

## Testing

Add regression coverage for V2 inventory sharing and refresh, environment isolation, catalog merging, partial Cloud results, disabled plugins, and catalog consistency across steps and read routes.

GitOrigin-RevId: 842bdcbc9e19364dd69a9abf9e48330b7425a76c

codex-rs/exec-server-protocol/src/capabilities.rs

@@ -20,6 +20,18 @@ pub struct ExecutorCapabilityDiscoveryV2Snapshot {
     pub result: Result<Arc<DiscoverV2CapabilitiesResponse>, String>,
 }
 
+impl ExecutorCapabilityDiscoveryV2Snapshot {
+    /// Compares discovery identity, not inventory contents; repeated errors compare by message.
+    pub fn same_discovery(&self, other: &Self) -> bool {
+        self.environment_id == other.environment_id
+            && match (&self.result, &other.result) {
+                (Ok(previous), Ok(current)) => Arc::ptr_eq(previous, current),
+                (Err(previous), Err(current)) => previous == current,
+                (Ok(_), Err(_)) | (Err(_), Ok(_)) => false,
+            }
+    }
+}
+
 /// Discover installed capabilities for a thread, without client-supplied installation paths.
 #[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
 #[serde(rename_all = "camelCase")]

codex-rs/exec-server-protocol/src/capabilities_tests.rs

@@ -1,4 +1,4 @@
-//! V2 discovery requests and responses round-trip through JSON.
+//! V2 discovery wire contracts.
 
 use super::*;
 use crate::CapabilityTextFile;