Attribute command and plugin analytics to the invoking model (#45445)

## Why

Command execution and plugin measurement events lack model and reasoning-effort labels. Attribution needs to reflect the step that invoked the command, even when model settings change before a background process finishes.

## What changed

- Add `model_slug` and `reasoning_effort` to command execution and plugin measurement analytics.
- Capture model context from resolved step settings and carry it through execution, approval, Guardian review, and plugin metrics collection.
- Preserve the first command-start model context when subsequent start notifications arrive.
- Keep the carried context out of serialized protocol items and generated schemas.

## Testing

Extend analytics tests to cover model switches before invocation and during background execution, default reasoning effort, Guardian-denied commands, and repeated start notifications retaining the original model context.

GitOrigin-RevId: af90e1c0d39bab625f2e89786085b61a9b96c0ce

codex-rs/core/src/unified_exec/async_watcher.rs

@@ -178,6 +178,7 @@ pub(crate) fn spawn_exit_watcher(
     let session_ref = Arc::clone(&context.session);
     let turn_ref = Arc::clone(&context.step_context.turn);
     let model_info = Arc::clone(&context.step_context.settings.model_info);
+    let model_context = context.step_context.model_context();
     let call_id = context.call_id.clone();
     let exit_token = process.cancellation_token();
     let output_drained = process.output_drained_notify();
@@ -223,6 +224,7 @@ pub(crate) fn spawn_exit_watcher(
                 exit_code,
                 &session_ref,
                 &turn_ref,
+                &model_context,
                 &call_id,
             )
             .await;

codex-rs/core/src/unified_exec/process_manager.rs

@@ -276,11 +276,13 @@ struct InitialExecCommandGuard {
 
 impl InitialExecCommandGuard {
     async fn finish_plugin_metrics(&mut self, context: &UnifiedExecContext, exit_code: i32) {
+        let model_context = context.step_context.model_context();
         finish_and_track_measurements(
             self.metrics_sidecar.take(),
             exit_code,
             &context.session,
             &context.step_context.turn,
+            &model_context,
             &context.call_id,
         )
         .await;
@@ -530,13 +532,15 @@ impl UnifiedExecProcessManager {
         });
 
         let transcript = Arc::new(tokio::sync::Mutex::new(HeadTailBuffer::default()));
-        let event_ctx = ToolEventCtx::new(
+        let model_context = context.step_context.model_context();
+        let mut event_ctx = ToolEventCtx::new(
             context.session.as_ref(),
             context.step_context.turn.as_ref(),
             &context.step_context.settings.model_info,
             &context.call_id,
             /*turn_diff_tracker*/ None,
         );
+        event_ctx.model_context = Some(&model_context);
         let plugin_attribution = if request.turn_environment.environment.is_remote() {
             let file_system = request.turn_environment.environment.get_filesystem();
             context
@@ -727,6 +731,7 @@ impl UnifiedExecProcessManager {
                         exit_code.unwrap_or(-1),
                         &context.session,
                         &context.step_context.turn,
+                        &model_context,
                         &context.call_id,
                     )
                     .await;