Support SYSTEM skills. (#8220)

1. Remove PUBLIC skills and introduce SYSTEM skills embedded in the
binary and installed into $CODEX_HOME/skills/.system at startup.
2. Skills are now always enabled (feature flag removed).
3. Update skills/list to accept forceReload and plumb it through (not
used by clients yet).

codex-rs/app-server-protocol/src/protocol/v2.rs

@@ -980,6 +980,10 @@ pub struct SkillsListParams {
     /// When empty, defaults to the current session working directory.
     #[serde(default, skip_serializing_if = "Vec::is_empty")]
     pub cwds: Vec<PathBuf>,
+
+    /// When true, bypass the skills cache and re-scan skills from disk.
+    #[serde(default, skip_serializing_if = "std::ops::Not::not")]
+    pub force_reload: bool,
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
@@ -996,7 +1000,7 @@ pub struct SkillsListResponse {
 pub enum SkillScope {
     User,
     Repo,
-    Public,
+    System,
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
@@ -1042,7 +1046,7 @@ impl From<CoreSkillScope> for SkillScope {
         match value {
             CoreSkillScope::User => Self::User,
             CoreSkillScope::Repo => Self::Repo,
-            CoreSkillScope::Public => Self::Public,
+            CoreSkillScope::System => Self::System,
         }
     }
 }
@@ -1939,6 +1943,30 @@ mod tests {
         );
     }
 
+    #[test]
+    fn skills_list_params_serialization_uses_force_reload() {
+        assert_eq!(
+            serde_json::to_value(SkillsListParams {
+                cwds: Vec::new(),
+                force_reload: false,
+            })
+            .unwrap(),
+            json!({}),
+        );
+
+        assert_eq!(
+            serde_json::to_value(SkillsListParams {
+                cwds: vec![PathBuf::from("/repo")],
+                force_reload: true,
+            })
+            .unwrap(),
+            json!({
+                "cwds": ["/repo"],
+                "forceReload": true,
+            }),
+        );
+    }
+
     #[test]
     fn codex_error_info_serializes_http_status_code_in_camel_case() {
         let value = CodexErrorInfo::ResponseTooManyFailedAttempts {