feat(app-server): add optional thread_id to experimentalFeature/list (#23335)

## Why

`experimentalFeature/list` reports effective feature enablement, but
currently does not resolve it against a working directory where
project-local config.toml files can exist and toggle on/off features
when merged into the effective config after resolving the various config
layers. That means we effectively (and incorrectly) ignore features set
in project-local config.

To address that, this PR exposes an optional `thread_id` param which
allows us to load the thread's `cwd.

## Testing

- `cargo test -p codex-app-server-protocol`
- `cargo test -p codex-app-server experimental_feature_list`

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

@@ -2721,7 +2721,33 @@ mod tests {
                 "id": 8,
                 "params": {
                     "cursor": null,
-                    "limit": null
+                    "limit": null,
+                    "threadId": null
+                }
+            }),
+            serde_json::to_value(&request)?,
+        );
+        Ok(())
+    }
+
+    #[test]
+    fn serialize_list_experimental_features_with_thread_id() -> Result<()> {
+        let request = ClientRequest::ExperimentalFeatureList {
+            request_id: RequestId::Integer(8),
+            params: v2::ExperimentalFeatureListParams {
+                cursor: Some("3".to_string()),
+                limit: Some(2),
+                thread_id: Some("00000000-0000-4000-8000-000000000001".to_string()),
+            },
+        };
+        assert_eq!(
+            json!({
+                "method": "experimentalFeature/list",
+                "id": 8,
+                "params": {
+                    "cursor": "3",
+                    "limit": 2,
+                    "threadId": "00000000-0000-4000-8000-000000000001"
                 }
             }),
             serde_json::to_value(&request)?,

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

@@ -14,6 +14,11 @@ pub struct ExperimentalFeatureListParams {
     /// Optional page size; defaults to a reasonable server-side value.
     #[ts(optional = nullable)]
     pub limit: Option<u32>,
+    /// Optional loaded thread id. Pass this when showing feature state for an
+    /// existing thread so enablement is computed from that thread's refreshed
+    /// config, including project-local config for the thread's cwd.
+    #[ts(optional = nullable)]
+    pub thread_id: Option<String>,
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]