Extract codex-plugin crate (#15747)

## Summary
- extract plugin identifiers and load-outcome types into codex-plugin
- update codex-core to consume the new plugin crate

## Testing
- CI

---------

Co-authored-by: Codex <noreply@openai.com>

codex-rs/plugin/src/lib.rs

@@ -0,0 +1,55 @@
+//! Shared plugin identifiers and telemetry-facing summaries.
+
+pub use codex_utils_plugins::PLUGIN_MANIFEST_PATH;
+pub use codex_utils_plugins::mention_syntax;
+pub use codex_utils_plugins::plugin_namespace_for_skill_path;
+
+mod load_outcome;
+mod plugin_id;
+
+pub use load_outcome::EffectiveSkillRoots;
+pub use load_outcome::LoadedPlugin;
+pub use load_outcome::PluginLoadOutcome;
+pub use load_outcome::prompt_safe_plugin_description;
+pub use plugin_id::PluginId;
+pub use plugin_id::PluginIdError;
+pub use plugin_id::validate_plugin_segment;
+
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub struct AppConnectorId(pub String);
+
+#[derive(Debug, Clone, Default, PartialEq, Eq)]
+pub struct PluginCapabilitySummary {
+    pub config_name: String,
+    pub display_name: String,
+    pub description: Option<String>,
+    pub has_skills: bool,
+    pub mcp_server_names: Vec<String>,
+    pub app_connector_ids: Vec<AppConnectorId>,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct PluginTelemetryMetadata {
+    pub plugin_id: PluginId,
+    pub capability_summary: Option<PluginCapabilitySummary>,
+}
+
+impl PluginTelemetryMetadata {
+    pub fn from_plugin_id(plugin_id: &PluginId) -> Self {
+        Self {
+            plugin_id: plugin_id.clone(),
+            capability_summary: None,
+        }
+    }
+}
+
+impl PluginCapabilitySummary {
+    pub fn telemetry_metadata(&self) -> Option<PluginTelemetryMetadata> {
+        PluginId::parse(&self.config_name)
+            .ok()
+            .map(|plugin_id| PluginTelemetryMetadata {
+                plugin_id,
+                capability_summary: Some(self.clone()),
+            })
+    }
+}