Reconcile V2 executor plugins with cloud catalogs (#55301)

## What changed

- Use V2 discovery inventories for plugin MCP contributions when supplied, including empty or failed inventories; retain legacy discovery when no V2 snapshot is supplied.
- Merge plugins by canonical identity, using cloud metadata and enablement for remote plugins and attaching executor installations only when versions match. Preserve configured executor-local plugins and executor enablement when cloud data is unavailable.
- Keep installation order stable across refreshes and run merged MCP declarations on the first retained executor installation while preserving attribution for the others.
- Carry local and remote identities through selected-plugin snapshots, skill attribution, and active-plugin telemetry. Track disabled plugin IDs alongside disabled roots.
- Preserve a complete cloud catalog when a partial refresh arrives, and cap tool-description plugin attribution at 1,024 bytes while retaining all plugin associations.

## Testing

Add coverage for catalog parsing and reconciliation, enablement and discovery-mode selection, installation refresh ordering, executor-specific MCP normalization, selected-plugin snapshots, and bounded UTF-8 attribution text.

GitOrigin-RevId: a8ad352de6a2b8dc4bfd1ff6a5c62ee8ed1d1664

codex-rs/core-plugin-common/src/identity.rs

@@ -0,0 +1,20 @@
+//! Source-neutral identity shared by plugin catalogs and runtime attribution.
+
+/// Stable key used to merge discoveries of the same logical plugin.
+/// Identity is independent of whether the plugin is supplied by the cloud or an executor.
+#[derive(Clone, Debug, PartialEq, Eq, Hash)]
+pub enum PluginIdentity {
+    /// Stable ID assigned by plugin-service and shared by its materialized installations.
+    Remote { remote_plugin_id: String },
+    /// Local config key (normally `name@marketplace`), or a legacy selected-root identity.
+    Local { plugin_id: String },
+}
+
+impl PluginIdentity {
+    pub fn as_str(&self) -> &str {
+        match self {
+            Self::Remote { remote_plugin_id } => remote_plugin_id,
+            Self::Local { plugin_id } => plugin_id,
+        }
+    }
+}

codex-rs/core-plugin-common/src/lib.rs

@@ -1,4 +1,7 @@
 //! Shared plugin identities and read-only installed-package rules.
 
+mod identity;
 pub mod installed;
 pub mod plugin_id;
+
+pub use identity::PluginIdentity;