2- Use string service tiers in session protocol (#20971)

## Summary
- break service tier session/op/app-server protocol fields from the
closed enum to string tier ids
- send the service tier string directly through model requests, prewarm,
compaction, memories, and TUI/app-server turn starts
- regenerate app-server protocol JSON/TypeScript schemas, removing the
standalone ServiceTier TS enum

## Verification
- just fmt
- cargo check -p codex-core -p codex-app-server -p codex-tui
- just write-app-server-schema

---------

Co-authored-by: Codex <noreply@openai.com>

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

@@ -5,7 +5,6 @@ use super::shared::default_enabled;
 use codex_experimental_api_macros::ExperimentalApi;
 use codex_protocol::config_types::ForcedLoginMethod;
 use codex_protocol::config_types::ReasoningSummary;
-use codex_protocol::config_types::ServiceTier;
 use codex_protocol::config_types::Verbosity;
 use codex_protocol::config_types::WebSearchMode;
 use codex_protocol::config_types::WebSearchToolConfig;
@@ -137,7 +136,7 @@ pub struct ProfileV2 {
     /// used.
     #[experimental("config/read.approvalsReviewer")]
     pub approvals_reviewer: Option<ApprovalsReviewer>,
-    pub service_tier: Option<ServiceTier>,
+    pub service_tier: Option<String>,
     pub model_reasoning_effort: Option<ReasoningEffort>,
     pub model_reasoning_summary: Option<ReasoningSummary>,
     pub model_verbosity: Option<Verbosity>,
@@ -248,7 +247,7 @@ pub struct Config {
     pub model_reasoning_effort: Option<ReasoningEffort>,
     pub model_reasoning_summary: Option<ReasoningSummary>,
     pub model_verbosity: Option<Verbosity>,
-    pub service_tier: Option<ServiceTier>,
+    pub service_tier: Option<String>,
     pub analytics: Option<AnalyticsConfig>,
     #[experimental("config/read.apps")]
     #[serde(default)]

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

@@ -12,7 +12,6 @@ use super::TurnEnvironmentParams;
 use super::shared::v2_enum_from_core;
 use codex_experimental_api_macros::ExperimentalApi;
 use codex_protocol::config_types::Personality;
-use codex_protocol::config_types::ServiceTier;
 use codex_protocol::models::ResponseItem;
 use codex_protocol::openai_models::ReasoningEffort;
 use codex_protocol::protocol::ThreadGoalStatus as CoreThreadGoalStatus;
@@ -103,7 +102,7 @@ pub struct ThreadStartParams {
         skip_serializing_if = "Option::is_none"
     )]
     #[ts(optional = nullable)]
-    pub service_tier: Option<Option<ServiceTier>>,
+    pub service_tier: Option<Option<String>>,
     #[ts(optional = nullable)]
     pub cwd: Option<String>,
     #[experimental(nested)]
@@ -192,7 +191,7 @@ pub struct ThreadStartResponse {
     pub thread: Thread,
     pub model: String,
     pub model_provider: String,
-    pub service_tier: Option<ServiceTier>,
+    pub service_tier: Option<String>,
     pub cwd: AbsolutePathBuf,
     /// Instruction source files currently loaded for this thread.
     #[serde(default)]
@@ -260,7 +259,7 @@ pub struct ThreadResumeParams {
         skip_serializing_if = "Option::is_none"
     )]
     #[ts(optional = nullable)]
-    pub service_tier: Option<Option<ServiceTier>>,
+    pub service_tier: Option<Option<String>>,
     #[ts(optional = nullable)]
     pub cwd: Option<String>,
     #[experimental(nested)]
@@ -307,7 +306,7 @@ pub struct ThreadResumeResponse {
     pub thread: Thread,
     pub model: String,
     pub model_provider: String,
-    pub service_tier: Option<ServiceTier>,
+    pub service_tier: Option<String>,
     pub cwd: AbsolutePathBuf,
     /// Instruction source files currently loaded for this thread.
     #[serde(default)]
@@ -366,7 +365,7 @@ pub struct ThreadForkParams {
         skip_serializing_if = "Option::is_none"
     )]
     #[ts(optional = nullable)]
-    pub service_tier: Option<Option<ServiceTier>>,
+    pub service_tier: Option<Option<String>>,
     #[ts(optional = nullable)]
     pub cwd: Option<String>,
     #[experimental(nested)]
@@ -416,7 +415,7 @@ pub struct ThreadForkResponse {
     pub thread: Thread,
     pub model: String,
     pub model_provider: String,
-    pub service_tier: Option<ServiceTier>,
+    pub service_tier: Option<String>,
     pub cwd: AbsolutePathBuf,
     /// Instruction source files currently loaded for this thread.
     #[serde(default)]

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

@@ -7,7 +7,6 @@ use codex_experimental_api_macros::ExperimentalApi;
 use codex_protocol::config_types::CollaborationMode;
 use codex_protocol::config_types::Personality;
 use codex_protocol::config_types::ReasoningSummary;
-use codex_protocol::config_types::ServiceTier;
 use codex_protocol::openai_models::ReasoningEffort;
 use codex_protocol::plan_tool::PlanItemArg as CorePlanItemArg;
 use codex_protocol::plan_tool::StepStatus as CorePlanStepStatus;
@@ -94,7 +93,7 @@ pub struct TurnStartParams {
         skip_serializing_if = "Option::is_none"
     )]
     #[ts(optional = nullable)]
-    pub service_tier: Option<Option<ServiceTier>>,
+    pub service_tier: Option<Option<String>>,
     /// Override the reasoning effort for this turn and subsequent turns.
     #[ts(optional = nullable)]
     pub effort: Option<ReasoningEffort>,