[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/codex-backend-openapi-models/src/models/mod.rs

@@ -32,6 +32,8 @@ pub use self::additional_rate_limit_details::AdditionalRateLimitDetails;
 
 pub(crate) mod rate_limit_status_payload;
 pub use self::rate_limit_status_payload::PlanType;
+pub use self::rate_limit_status_payload::RateLimitReachedKind;
+pub use self::rate_limit_status_payload::RateLimitReachedType;
 pub use self::rate_limit_status_payload::RateLimitStatusPayload;
 
 pub(crate) mod rate_limit_status_details;

codex-rs/codex-backend-openapi-models/src/models/rate_limit_status_payload.rs

@@ -37,6 +37,13 @@ pub struct RateLimitStatusPayload {
         skip_serializing_if = "Option::is_none"
     )]
     pub additional_rate_limits: Option<Option<Vec<models::AdditionalRateLimitDetails>>>,
+    #[serde(
+        rename = "rate_limit_reached_type",
+        default,
+        with = "::serde_with::rust::double_option",
+        skip_serializing_if = "Option::is_none"
+    )]
+    pub rate_limit_reached_type: Option<Option<RateLimitReachedType>>,
 }
 
 impl RateLimitStatusPayload {
@@ -46,10 +53,36 @@ impl RateLimitStatusPayload {
             rate_limit: None,
             credits: None,
             additional_rate_limits: None,
+            rate_limit_reached_type: None,
         }
     }
 }
 
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+pub struct RateLimitReachedType {
+    #[serde(rename = "type")]
+    pub kind: RateLimitReachedKind,
+}
+
+#[derive(
+    Clone, Copy, Debug, Eq, PartialEq, Ord, PartialOrd, Hash, Serialize, Deserialize, Default,
+)]
+pub enum RateLimitReachedKind {
+    #[serde(rename = "rate_limit_reached")]
+    RateLimitReached,
+    #[serde(rename = "workspace_owner_credits_depleted")]
+    WorkspaceOwnerCreditsDepleted,
+    #[serde(rename = "workspace_member_credits_depleted")]
+    WorkspaceMemberCreditsDepleted,
+    #[serde(rename = "workspace_owner_usage_limit_reached")]
+    WorkspaceOwnerUsageLimitReached,
+    #[serde(rename = "workspace_member_usage_limit_reached")]
+    WorkspaceMemberUsageLimitReached,
+    #[serde(rename = "unknown", other)]
+    #[default]
+    Unknown,
+}
+
 #[derive(
     Clone, Copy, Debug, Eq, PartialEq, Ord, PartialOrd, Hash, Serialize, Deserialize, Default,
 )]