Expose model settings in app-server thread metadata (#42151)

## What changed

- Add nullable `model` and `reasoningEffort` fields to the shared app-server `Thread` object and generated schemas.
- Report current settings for loaded threads and the latest persisted settings for unloaded threads across thread read, list, start, resume, rollback, metadata update, and notification paths.
- Keep unavailable legacy or filesystem-only settings nullable, and allow metadata reads without loading a thread or dispatching queued work.

## Testing

- Cover live-setting precedence, persisted settings after restart, null legacy values, and model metadata returned by thread lifecycle operations.

GitOrigin-RevId: 22ebe8a8d1910a820d90a97730d812a00d8c1372

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

@@ -3130,6 +3130,8 @@ mod tests {
                     project_id: None,
                     history_mode: Default::default(),
                     model_provider: "openai".to_string(),
+                    model: None,
+                    reasoning_effort: None,
                     created_at: 1,
                     updated_at: 2,
                     recency_at: Some(3),
@@ -3185,6 +3187,8 @@ mod tests {
                         "projectId": null,
                         "historyMode": "legacy",
                         "modelProvider": "openai",
+                        "model": null,
+                        "reasoningEffort": null,
                         "createdAt": 1,
                         "updatedAt": 2,
                         "recencyAt": 3,

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

@@ -288,6 +288,8 @@ fn thread_resume_response_round_trips_initial_turns_page() {
             project_id: None,
             history_mode: Default::default(),
             model_provider: "openai".to_string(),
+            model: None,
+            reasoning_effort: None,
             created_at: 1,
             updated_at: 1,
             recency_at: Some(1),

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

@@ -5,6 +5,7 @@ use super::TurnStatus;
 use crate::JsonSchema;
 use crate::TS;
 use codex_experimental_api_macros::ExperimentalApi;
+use codex_protocol::openai_models::ReasoningEffort;
 use codex_protocol::protocol::MisalignmentErrorDetails as CoreMisalignmentErrorDetails;
 use codex_protocol::protocol::MisalignmentSteer as CoreMisalignmentSteer;
 use codex_protocol::protocol::SessionSource as CoreSessionSource;
@@ -233,6 +234,12 @@ pub struct Thread {
     pub history_mode: ThreadHistoryMode,
     /// Model provider used for this thread (for example, 'openai').
     pub model_provider: String,
+    /// Current configured model when loaded, otherwise the latest persisted model.
+    /// Null when unavailable. This is not per-turn execution telemetry.
+    pub model: Option<String>,
+    /// Current configured reasoning effort when loaded, otherwise the latest persisted effort.
+    /// Null when unset or unavailable. This is not per-turn execution telemetry.
+    pub reasoning_effort: Option<ReasoningEffort>,
     /// Unix timestamp (in seconds) when the thread was created.
     #[ts(type = "number")]
     pub created_at: i64,
@@ -294,6 +301,8 @@ struct ThreadCompatibility {
     #[serde(default)]
     history_mode: ThreadHistoryMode,
     model_provider: String,
+    model: Option<String>,
+    reasoning_effort: Option<ReasoningEffort>,
     created_at: i64,
     updated_at: i64,
     recency_at: Option<i64>,
@@ -330,6 +339,8 @@ impl<'de> Deserialize<'de> for Thread {
             project_id: thread.project_id,
             history_mode: thread.history_mode,
             model_provider: thread.model_provider,
+            model: thread.model,
+            reasoning_effort: thread.reasoning_effort,
             created_at: thread.created_at,
             updated_at: thread.updated_at,
             recency_at: thread.recency_at,