[app-server] Include reset-credit details in rate limits (#30395)

## Why

Supported clients currently receive only a reset-credit count from
`account/rateLimits/read`. The redemption UI and other app-server
clients need each available credit's expiry and ID so they can explain
what will expire and consume the credit a user selected. This
information belongs on the existing rate-limit read surface rather than
a second app-server list RPC that clients would need to coordinate.

## What changed

- extend `rateLimitResetCredits` on `account/rateLimits/read` with
nullable `credits` detail rows
- fetch usage and reset-credit details concurrently; if the detail
request fails, times out, or cannot be parsed, preserve the usage
response and return `credits: null`
- expose each credit's ID, reset type, status, grant time, expiry time,
title, and description
- add an optional nullable `creditId` to
`account/rateLimitResetCredit/consume`; omitting it preserves the
existing automatic-selection behavior
- forward a selected credit ID to the Codex backend and update the
app-server documentation and generated schemas

The TUI consumer is stacked in #30488.

## Validation

- `just test -p codex-app-server-protocol` (251 passed)
- `just test -p codex-backend-client` (16 passed)
- `just test -p codex-app-server rate_limit` (18 passed)

Part of #29618.

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

@@ -284,6 +284,52 @@ pub struct GetAccountRateLimitsResponse {
 #[ts(export_to = "v2/")]
 pub struct RateLimitResetCreditsSummary {
     pub available_count: i64,
+    /// Detail rows for available reset credits, when the backend provides them.
+    ///
+    /// `null` means only `availableCount` is known, while an empty array means details were fetched
+    /// and no available credits were returned. The backend may cap this list, so its length can be
+    /// less than `availableCount`.
+    pub credits: Option<Vec<RateLimitResetCredit>>,
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct RateLimitResetCredit {
+    /// Opaque backend identifier for this reset credit.
+    pub id: String,
+    pub reset_type: RateLimitResetType,
+    pub status: RateLimitResetCreditStatus,
+    /// Unix timestamp in seconds when the credit was granted.
+    #[ts(type = "number")]
+    pub granted_at: i64,
+    /// Unix timestamp in seconds when the credit expires, or `null` if it does not expire.
+    #[ts(type = "number | null")]
+    pub expires_at: Option<i64>,
+    /// Backend-provided display title for this credit, or `null` when unavailable.
+    pub title: Option<String>,
+    /// Backend-provided display description for this credit, or `null` when unavailable.
+    pub description: Option<String>,
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, Copy, PartialEq, Eq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/", rename_all = "camelCase")]
+pub enum RateLimitResetType {
+    CodexRateLimits,
+    #[serde(other)]
+    Unknown,
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, Copy, PartialEq, Eq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/", rename_all = "camelCase")]
+pub enum RateLimitResetCreditStatus {
+    Available,
+    Redeeming,
+    Redeemed,
+    #[serde(other)]
+    Unknown,
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]
@@ -293,6 +339,10 @@ pub struct ConsumeAccountRateLimitResetCreditParams {
     /// Identifies one logical reset attempt. A UUID is recommended; reuse the same value when
     /// retrying that attempt.
     pub idempotency_key: String,
+    /// Opaque reset-credit identifier to redeem. When omitted, the backend selects the next
+    /// available credit.
+    #[ts(optional = nullable)]
+    pub credit_id: Option<String>,
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]