[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/README.md

@@ -188,7 +188,7 @@ Example with notification opt-out:
 - `fs/watch` — subscribe this connection to filesystem change notifications for an absolute file or directory path and caller-provided `watchId`; returns the canonicalized `path`.
 - `fs/unwatch` — stop sending notifications for a prior `fs/watch`; returns `{}`.
 - `fs/changed` — notification emitted when watched paths change, including the `watchId` and `changedPaths`.
-- `model/list` — list available models (set `includeHidden: true` to include entries with `hidden: true`), with reasoning effort options, `additionalSpeedTiers`, `serviceTiers`, optional `defaultServiceTier`, optional legacy `upgrade` model ids, optional `upgradeInfo` metadata (`model`, `upgradeCopy`, `modelLink`, `migrationMarkdown`), and optional `availabilityNux` metadata.
+- `model/list` — list available models (set `includeHidden: true` to include entries with `hidden: true`), with model-advertised string reasoning effort options, `additionalSpeedTiers`, `serviceTiers`, optional `defaultServiceTier`, optional legacy `upgrade` model ids, optional `upgradeInfo` metadata (`model`, `upgradeCopy`, `modelLink`, `migrationMarkdown`), and optional `availabilityNux` metadata.
 - `modelProvider/capabilities/read` — read provider-level capabilities for the currently configured model provider.
 - `experimentalFeature/list` — list feature flags with stage metadata (`beta`, `underDevelopment`, `stable`, etc.), enabled/default-enabled state, and cursor pagination. Pass `threadId` when showing feature state for an existing loaded thread so `enabled` is computed from that thread's refreshed config, including project-local config for the thread's cwd; if omitted, the server uses its default config resolution context. For non-beta flags, `displayName`/`description`/`announcement` are `null`.
 - `permissionProfile/list` — beta; list available permission profile ids with optional display `description` text, using cursor pagination. Pass `cwd` when the caller needs project-local `[permissions.<id>]` entries to be included in the current catalog view.

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(),

codex-rs/app-server/tests/common/models_cache.rs

@@ -18,7 +18,7 @@ fn preset_to_info(preset: &ModelPreset, priority: i32) -> ModelInfo {
         slug: preset.id.clone(),
         display_name: preset.display_name.clone(),
         description: Some(preset.description.clone()),
-        default_reasoning_level: Some(preset.default_reasoning_effort),
+        default_reasoning_level: Some(preset.default_reasoning_effort.clone()),
         supported_reasoning_levels: preset.supported_reasoning_efforts.clone(),
         shell_type: ConfigShellToolType::ShellCommand,
         visibility: if preset.show_in_picker {

codex-rs/app-server/tests/suite/v2/model_list.rs

@@ -48,11 +48,11 @@ fn model_from_preset(preset: &ModelPreset) -> Model {
             .supported_reasoning_efforts
             .iter()
             .map(|preset| ReasoningEffortOption {
-                reasoning_effort: preset.effort,
+                reasoning_effort: preset.effort.clone(),
                 description: preset.description.clone(),
             })
             .collect(),
-        default_reasoning_effort: preset.default_reasoning_effort,
+        default_reasoning_effort: preset.default_reasoning_effort.clone(),
         input_modalities: preset.input_modalities.clone(),
         // `write_models_cache()` round-trips through a simplified ModelInfo fixture that does not
         // preserve personality placeholders in base instructions, so app-server list results from
@@ -164,10 +164,10 @@ async fn list_models_uses_chatgpt_remote_catalog_as_source_of_truth() -> Result<
         "slug": "chatgpt-remote-only",
         "display_name": "ChatGPT Remote Only",
         "description": "Remote-only model for app-server model/list coverage",
-        "default_reasoning_level": "medium",
+        "default_reasoning_level": "max",
         "supported_reasoning_levels": [
             {"effort": "low", "description": "low"},
-            {"effort": "medium", "description": "medium"}
+            {"effort": "max", "description": "Maximum"}
         ],
         "shell_type": "shell_command",
         "visibility": "list",