[codex] Propagate rate limit reached type (#18227)

## Summary

First PR in the split from #17956.

- adds the core/app-server `RateLimitReachedType` shape
- maps backend `rate_limit_reached_type` into Codex rate-limit snapshots
- carries the field through app-server notifications/responses and
generated schemas
- updates existing constructors/tests for the new optional field

## Validation

- `cargo test -p codex-backend-client`
- `cargo test -p codex-app-server-protocol`
- `cargo test -p codex-app-server rate_limits`
- `cargo test -p codex-tui workspace_`
- `cargo test -p codex-tui status_`
- `just fmt`
- `just fix -p codex-backend-client`
- `just fix -p codex-app-server-protocol`
- `just fix -p codex-app-server`
- `just fix -p codex-tui`

codex-rs/tui/src/chatwidget/tests/helpers.rs

@@ -106,6 +106,7 @@ pub(super) fn snapshot(percent: f64) -> RateLimitSnapshot {
         secondary: None,
         credits: None,
         plan_type: None,
+        rate_limit_reached_type: None,
     }
 }
 

codex-rs/tui/src/chatwidget/tests/status_and_layout.rs

@@ -235,6 +235,7 @@ async fn rate_limit_snapshot_keeps_prior_credits_when_missing_from_headers() {
             balance: Some("17.5".to_string()),
         }),
         plan_type: None,
+        rate_limit_reached_type: None,
     }));
     let initial_balance = chat
         .rate_limit_snapshots_by_limit_id
@@ -254,6 +255,7 @@ async fn rate_limit_snapshot_keeps_prior_credits_when_missing_from_headers() {
         secondary: None,
         credits: None,
         plan_type: None,
+        rate_limit_reached_type: None,
     }));
 
     let display = chat
@@ -292,6 +294,7 @@ async fn rate_limit_snapshot_updates_and_retains_plan_type() {
         }),
         credits: None,
         plan_type: Some(PlanType::Plus),
+        rate_limit_reached_type: None,
     }));
     assert_eq!(chat.plan_type, Some(PlanType::Plus));
 
@@ -310,6 +313,7 @@ async fn rate_limit_snapshot_updates_and_retains_plan_type() {
         }),
         credits: None,
         plan_type: Some(PlanType::Pro),
+        rate_limit_reached_type: None,
     }));
     assert_eq!(chat.plan_type, Some(PlanType::Pro));
 
@@ -328,6 +332,7 @@ async fn rate_limit_snapshot_updates_and_retains_plan_type() {
         }),
         credits: None,
         plan_type: None,
+        rate_limit_reached_type: None,
     }));
     assert_eq!(chat.plan_type, Some(PlanType::Pro));
 }
@@ -351,6 +356,7 @@ async fn rate_limit_snapshots_keep_separate_entries_per_limit_id() {
             balance: Some("5.00".to_string()),
         }),
         plan_type: Some(PlanType::Pro),
+        rate_limit_reached_type: None,
     }));
 
     chat.on_rate_limit_snapshot(Some(RateLimitSnapshot {
@@ -364,6 +370,7 @@ async fn rate_limit_snapshots_keep_separate_entries_per_limit_id() {
         secondary: None,
         credits: None,
         plan_type: Some(PlanType::Pro),
+        rate_limit_reached_type: None,
     }));
 
     let codex = chat
@@ -416,6 +423,7 @@ async fn rate_limit_switch_prompt_skips_non_codex_limit() {
         secondary: None,
         credits: None,
         plan_type: None,
+        rate_limit_reached_type: None,
     }));
 
     assert!(matches!(