[app-server] add thread/tokenUsage/updated v2 event (#7268)

the TokenEvent event message becomes `thread/tokenUsage/updated` in v2.
before & after:
```
< {
<   "method": "codex/event/token_count",
<   "params": {
<     "conversationId": "019ab891-4c55-7790-9670-6c3b48c33281",
<     "id": "1",
<     "msg": {
<       "info": {
<         "last_token_usage": {
<           "cached_input_tokens": 3072,
<           "input_tokens": 5152,
<           "output_tokens": 16,
<           "reasoning_output_tokens": 0,
<           "total_tokens": 5168
<         },
<         "model_context_window": 258400,
<         "total_token_usage": {
<           "cached_input_tokens": 3072,
<           "input_tokens": 5152,
<           "output_tokens": 16,
<           "reasoning_output_tokens": 0,
<           "total_tokens": 5168
<         }
<       },
<       "rate_limits": {
<         "credits": null,
<         "primary": null,
<         "secondary": null
<       },
<       "type": "token_count"
<     }
<   }
< }
< {
<   "method": "thread/tokenUsage/updated",
<   "params": {
<     "threadId": "019ab891-4c55-7790-9670-6c3b48c33281",
<     "tokenUsage": {
<       "last": {
<         "cachedInputTokens": 3072,
<         "inputTokens": 5152,
<         "outputTokens": 16,
<         "reasoningOutputTokens": 0,
<         "totalTokens": 5168
<       },
<       "modelContextWindow": 258400,
<       "total": {
<         "cachedInputTokens": 3072,
<         "inputTokens": 5152,
<         "outputTokens": 16,
<         "reasoningOutputTokens": 0,
<         "totalTokens": 5168
<       }
<     },
<     "turnId": "1"
<   }
< }
```

Author: celia-oai

codex-rs/app-server-protocol/src/protocol/common.rs

@@ -502,6 +502,7 @@ server_notification_definitions! {
     /// NEW NOTIFICATIONS
     Error => "error" (v2::ErrorNotification),
     ThreadStarted => "thread/started" (v2::ThreadStartedNotification),
+    ThreadTokenUsageUpdated => "thread/tokenUsage/updated" (v2::ThreadTokenUsageUpdatedNotification),
     TurnStarted => "turn/started" (v2::TurnStartedNotification),
     TurnCompleted => "turn/completed" (v2::TurnCompletedNotification),
     TurnDiffUpdated => "turn/diff/updated" (v2::TurnDiffUpdatedNotification),

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

@@ -16,6 +16,8 @@ use codex_protocol::protocol::CreditsSnapshot as CoreCreditsSnapshot;
 use codex_protocol::protocol::RateLimitSnapshot as CoreRateLimitSnapshot;
 use codex_protocol::protocol::RateLimitWindow as CoreRateLimitWindow;
 use codex_protocol::protocol::SessionSource as CoreSessionSource;
+use codex_protocol::protocol::TokenUsage as CoreTokenUsage;
+use codex_protocol::protocol::TokenUsageInfo as CoreTokenUsageInfo;
 use codex_protocol::user_input::UserInput as CoreUserInput;
 use mcp_types::ContentBlock as McpContentBlock;
 use schemars::JsonSchema;
@@ -780,6 +782,63 @@ pub struct AccountUpdatedNotification {
     pub auth_mode: Option<AuthMode>,
 }
 
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct ThreadTokenUsageUpdatedNotification {
+    pub thread_id: String,
+    pub turn_id: String,
+    pub token_usage: ThreadTokenUsage,
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct ThreadTokenUsage {
+    pub total: TokenUsageBreakdown,
+    pub last: TokenUsageBreakdown,
+    #[ts(type = "number | null")]
+    pub model_context_window: Option<i64>,
+}
+
+impl From<CoreTokenUsageInfo> for ThreadTokenUsage {
+    fn from(value: CoreTokenUsageInfo) -> Self {
+        Self {
+            total: value.total_token_usage.into(),
+            last: value.last_token_usage.into(),
+            model_context_window: value.model_context_window,
+        }
+    }
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct TokenUsageBreakdown {
+    #[ts(type = "number")]
+    pub total_tokens: i64,
+    #[ts(type = "number")]
+    pub input_tokens: i64,
+    #[ts(type = "number")]
+    pub cached_input_tokens: i64,
+    #[ts(type = "number")]
+    pub output_tokens: i64,
+    #[ts(type = "number")]
+    pub reasoning_output_tokens: i64,
+}
+
+impl From<CoreTokenUsage> for TokenUsageBreakdown {
+    fn from(value: CoreTokenUsage) -> Self {
+        Self {
+            total_tokens: value.total_tokens,
+            input_tokens: value.input_tokens,
+            cached_input_tokens: value.cached_input_tokens,
+            output_tokens: value.output_tokens,
+            reasoning_output_tokens: value.reasoning_output_tokens,
+        }
+    }
+}
+
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
 #[serde(rename_all = "camelCase")]
 #[ts(export_to = "v2/")]

codex-rs/app-server/README.md

@@ -240,7 +240,7 @@ Event notifications are the server-initiated event stream for thread lifecycles,
 
 ### Turn events
 
-The app-server streams JSON-RPC notifications while a turn is running. Each turn starts with `turn/started` (initial `turn`) and ends with `turn/completed` (final `turn` plus token `usage`), and clients subscribe to the events they care about, rendering each item incrementally as updates arrive. The per-item lifecycle is always: `item/started` → zero or more item-specific deltas → `item/completed`.
+The app-server streams JSON-RPC notifications while a turn is running. Each turn starts with `turn/started` (initial `turn`) and ends with `turn/completed` (final `turn` status). Token usage events stream separately via `thread/tokenUsage/updated`. Clients subscribe to the events they care about, rendering each item incrementally as updates arrive. The per-item lifecycle is always: `item/started` → zero or more item-specific deltas → `item/completed`.
 
 - `turn/started` — `{ turn }` with the turn id, empty `items`, and `status: "inProgress"`.
 - `turn/completed` — `{ turn }` where `turn.status` is `completed`, `interrupted`, or `failed`; failures carry `{ error: { message, codexErrorInfo? } }`.