storing credits (#6858)

Expand the rate-limit cache/TUI: store credit snapshots alongside
primary and secondary windows, render “Credits” when the backend reports
they exist (unlimited vs rounded integer balances)

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

@@ -11,6 +11,7 @@ use codex_protocol::items::AgentMessageContent as CoreAgentMessageContent;
 use codex_protocol::items::TurnItem as CoreTurnItem;
 use codex_protocol::models::ResponseItem;
 use codex_protocol::parse_command::ParsedCommand as CoreParsedCommand;
+use codex_protocol::protocol::CreditsSnapshot as CoreCreditsSnapshot;
 use codex_protocol::protocol::RateLimitSnapshot as CoreRateLimitSnapshot;
 use codex_protocol::protocol::RateLimitWindow as CoreRateLimitWindow;
 use codex_protocol::user_input::UserInput as CoreUserInput;
@@ -994,6 +995,7 @@ pub struct AccountRateLimitsUpdatedNotification {
 pub struct RateLimitSnapshot {
     pub primary: Option<RateLimitWindow>,
     pub secondary: Option<RateLimitWindow>,
+    pub credits: Option<CreditsSnapshot>,
 }
 
 impl From<CoreRateLimitSnapshot> for RateLimitSnapshot {
@@ -1001,6 +1003,7 @@ impl From<CoreRateLimitSnapshot> for RateLimitSnapshot {
         Self {
             primary: value.primary.map(RateLimitWindow::from),
             secondary: value.secondary.map(RateLimitWindow::from),
+            credits: value.credits.map(CreditsSnapshot::from),
         }
     }
 }
@@ -1024,6 +1027,25 @@ impl From<CoreRateLimitWindow> for RateLimitWindow {
     }
 }
 
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct CreditsSnapshot {
+    pub has_credits: bool,
+    pub unlimited: bool,
+    pub balance: Option<String>,
+}
+
+impl From<CoreCreditsSnapshot> for CreditsSnapshot {
+    fn from(value: CoreCreditsSnapshot) -> Self {
+        Self {
+            has_credits: value.has_credits,
+            unlimited: value.unlimited,
+            balance: value.balance,
+        }
+    }
+}
+
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
 #[serde(rename_all = "camelCase")]
 #[ts(export_to = "v2/")]