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/core/src/session/turn.rs

@@ -73,6 +73,7 @@ use codex_hooks::HookEventAfterAgent;
 use codex_hooks::HookPayload;
 use codex_hooks::HookResult;
 use codex_protocol::config_types::ModeKind;
+use codex_protocol::config_types::ServiceTier;
 use codex_protocol::error::CodexErr;
 use codex_protocol::error::Result as CodexResult;
 use codex_protocol::items::PlanItem;
@@ -693,7 +694,11 @@ async fn track_turn_resolved_config_analytics(
             permission_profile_cwd: turn_context.cwd.to_path_buf(),
             reasoning_effort: turn_context.reasoning_effort,
             reasoning_summary: Some(turn_context.reasoning_summary),
-            service_tier: turn_context.config.service_tier,
+            service_tier: turn_context
+                .config
+                .service_tier
+                .as_deref()
+                .and_then(ServiceTier::from_request_value),
             approval_policy: turn_context.approval_policy.value(),
             approvals_reviewer: turn_context.config.approvals_reviewer,
             sandbox_network_access: turn_context.network_sandbox_policy().is_enabled(),
@@ -1858,7 +1863,7 @@ async fn try_run_sampling_request(
             &turn_context.session_telemetry,
             turn_context.reasoning_effort,
             turn_context.reasoning_summary,
-            turn_context.config.service_tier,
+            turn_context.config.service_tier.clone(),
             turn_metadata_header,
             &inference_trace,
         )