Preserve thread model settings across resume and revert (#55923)

## Why

Resuming a thread can replace saved model settings with global defaults. A selected service tier can also be lost when the current model does not support it.

## What changed

- Restore saved service tier, reasoning summary, and personality on resume unless the caller explicitly overrides them, respecting thread ownership of settings snapshots.
- Retain the selected service tier for persistence, settings notifications, and resume comparisons while filtering the effective tier against the current model's capabilities.
- Carry the runtime model, service tier, and personality into thread revert reconstruction.
- Persist initial thread settings before user input during MCP startup so an interrupted first turn retains its settings checkpoint.

## Testing

Extend regression coverage for cold resume and explicit overrides, unsupported service tiers, settings preservation during revert, and settings checkpoints before user input when MCP startup is interrupted.

GitOrigin-RevId: e5ec012a5678048c5eedd443e524f38c142bf9fd

codex-rs/app-server/src/request_processors/thread_processor.rs

@@ -5,6 +5,7 @@ mod daemon_continuation;
 mod daemon_snapshot;
 
 use super::persisted_resume_settings::PersistedResumeSettings;
+use super::persisted_resume_settings::latest_persisted_model_settings;
 use super::persisted_resume_settings::latest_persisted_resume_settings;
 use super::thread_enrichment::enrich_loaded_threads;
 use super::thread_fork_goal::inherit_thread_goal_snapshot;
@@ -120,6 +121,7 @@ struct ThreadRevertRuntimeSnapshot {
 fn collect_resume_override_mismatches(
     request: &ThreadResumeParams,
     config_snapshot: &ThreadConfigSnapshot,
+    selected_service_tier: Option<&str>,
 ) -> Vec<String> {
     let mut mismatch_details = Vec::new();
 
@@ -140,7 +142,7 @@ fn collect_resume_override_mismatches(
         ));
     }
     if let Some(requested_service_tier) = request.service_tier.as_ref()
-        && requested_service_tier != &config_snapshot.service_tier
+        && Some(requested_service_tier.as_deref().unwrap_or("default")) != selected_service_tier
     {
         mismatch_details.push(format!(
             "service_tier requested={requested_service_tier:?} active={:?}",
@@ -2405,10 +2407,17 @@ impl ThreadRequestProcessor {
         app_server_client_version: Option<String>,
     ) -> Result<ThreadRevertResponse, JSONRPCErrorError> {
         let ThreadRevertRuntimeSnapshot {
-            config,
+            mut config,
             settings,
             client_mcp_extensions,
         } = runtime_snapshot;
+        if let Some(collaboration_mode) = settings.collaboration_mode.as_ref() {
+            config.model = Some(collaboration_mode.model().to_string());
+        }
+        if let Some(service_tier) = settings.service_tier.as_ref() {
+            config.service_tier.clone_from(service_tier);
+        }
+        config.personality = settings.personality;
         let thread_id_string = thread_id.to_string();
         let stored_thread = self
             .read_stored_thread_for_resume(
@@ -4186,6 +4195,17 @@ impl ThreadRequestProcessor {
         }
         let has_explicit_model_resume_override =
             has_model_resume_override(request_overrides.as_ref(), &typesafe_overrides);
+        let persisted_model_settings = latest_persisted_model_settings(&thread_history);
+        let has_override = |key| {
+            request_overrides
+                .as_ref()
+                .is_some_and(|overrides| overrides.contains_key(key))
+        };
+        let restore_service_tier =
+            typesafe_overrides.service_tier.is_none() && !has_override("service_tier");
+        let restore_summary = !has_override("model_reasoning_summary");
+        let restore_personality =
+            typesafe_overrides.personality.is_none() && !has_override("personality");
         typesafe_overrides.persisted_permission_profile = history_settings
             .filter(|settings| {
                 settings.active_permission_profile.is_none()
@@ -4249,7 +4269,17 @@ impl ThreadRequestProcessor {
         if clear_reasoning_effort {
             config.model_reasoning_effort = None;
         }
-
+        if let Some(settings) = persisted_model_settings {
+            if restore_service_tier {
+                config.service_tier.clone_from(&settings.service_tier);
+            }
+            if restore_summary {
+                config.model_reasoning_summary = settings.reasoning_summary;
+            }
+            if restore_personality {
+                config.personality = settings.personality;
+            }
+        }
         let response_history = thread_history.clone();
 
         match self
@@ -4616,8 +4646,13 @@ impl ThreadRequestProcessor {
                     active_path.display()
                 )));
             }
-            let config_snapshot = existing_thread.config_snapshot().await;
-            let mismatch_details = collect_resume_override_mismatches(params, &config_snapshot);
+            let (config_snapshot, selected_service_tier) =
+                existing_thread.resume_config_snapshot().await;
+            let mismatch_details = collect_resume_override_mismatches(
+                params,
+                &config_snapshot,
+                selected_service_tier.as_deref(),
+            );
             if !mismatch_details.is_empty() {
                 let has_subscribers = !self
                     .thread_state_manager