[codex] Support model-defined reasoning efforts (#26444)

## Summary
- accept non-empty model-defined reasoning effort values while
preserving built-in effort behavior
- propagate the non-Copy effort type through core, app-server, TUI,
telemetry, and persistence call sites
- preserve string wire encoding and expose an open-string schema for
clients
- update model selection and shortcut behavior for model-advertised
effort values

## Root cause
`ReasoningEffort` gained a string-backed custom variant, so it could no
longer implement `Copy` or rely on derived closed-enum serialization.
Existing consumers still moved effort values from shared references and
assumed a fixed built-in value set.

## Validation
- `just fmt`
- Local tests and compilation were not run per request; relying on CI.

codex-rs/app-server/src/models.rs

@@ -62,10 +62,10 @@ fn reasoning_efforts_from_preset(
     efforts: Vec<ReasoningEffortPreset>,
 ) -> Vec<ReasoningEffortOption> {
     efforts
-        .iter()
+        .into_iter()
         .map(|preset| ReasoningEffortOption {
             reasoning_effort: preset.effort,
-            description: preset.description.to_string(),
+            description: preset.description,
         })
         .collect()
 }

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

@@ -158,7 +158,7 @@ fn merge_persisted_resume_metadata(
     typesafe_overrides.model = persisted_metadata.model.clone();
     typesafe_overrides.model_provider = Some(persisted_metadata.model_provider.clone());
 
-    if let Some(reasoning_effort) = persisted_metadata.reasoning_effort {
+    if let Some(reasoning_effort) = persisted_metadata.reasoning_effort.as_ref() {
         request_overrides.get_or_insert_with(HashMap::new).insert(
             "model_reasoning_effort".to_string(),
             serde_json::Value::String(reasoning_effort.to_string()),

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

@@ -203,7 +203,7 @@ pub(crate) fn thread_settings_from_config_snapshot(
         model: config_snapshot.model.clone(),
         model_provider: config_snapshot.model_provider_id.clone(),
         service_tier: config_snapshot.service_tier.clone(),
-        effort: config_snapshot.reasoning_effort,
+        effort: config_snapshot.reasoning_effort.clone(),
         summary: config_snapshot.reasoning_summary,
         collaboration_mode: config_snapshot.collaboration_mode.clone(),
         personality: config_snapshot.personality,

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

@@ -629,7 +629,7 @@ impl TurnRequestProcessor {
                     profile_workspace_roots: profile_workspace_roots.clone(),
                     windows_sandbox_level: None,
                     model: model.clone(),
-                    effort,
+                    effort: effort.clone(),
                     summary,
                     service_tier: service_tier.clone(),
                     collaboration_mode: collaboration_mode.clone(),