Expose model upgrade retirement times (#38449)

## What changed

- Parse the optional `retirement_at` RFC 3339 value from model upgrade metadata, treating missing, null, or malformed values as unknown.
- Expose known retirement times from `model/list` as nullable Unix timestamps in `upgradeInfo.retirementAt` and preserve them when converting app-server models back into model presets.
- Update the generated protocol schemas and app-server documentation.

## Testing

- Cover absent, null, valid, and malformed catalog values.
- Verify `model/list` serialization and app-server model conversion for known, missing, and out-of-range timestamps.

GitOrigin-RevId: 969baf9f5b012997f460fb4611ba63c963ee658c

codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.schemas.json

@@ -14041,6 +14041,14 @@
               "null"
             ]
           },
+          "retirementAt": {
+            "description": "Informational Unix timestamp for this upgrade's scheduled retirement, if known.",
+            "format": "int64",
+            "type": [
+              "integer",
+              "null"
+            ]
+          },
           "upgradeCopy": {
             "type": [
               "string",

codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.v2.schemas.json

@@ -10351,6 +10351,14 @@
             "null"
           ]
         },
+        "retirementAt": {
+          "description": "Informational Unix timestamp for this upgrade's scheduled retirement, if known.",
+          "format": "int64",
+          "type": [
+            "integer",
+            "null"
+          ]
+        },
         "upgradeCopy": {
           "type": [
             "string",

codex-rs/app-server-protocol/schema/json/v2/ModelListResponse.json

@@ -197,6 +197,14 @@
             "null"
           ]
         },
+        "retirementAt": {
+          "description": "Informational Unix timestamp for this upgrade's scheduled retirement, if known.",
+          "format": "int64",
+          "type": [
+            "integer",
+            "null"
+          ]
+        },
         "upgradeCopy": {
           "type": [
             "string",

codex-rs/app-server-protocol/schema/typescript/v2/ModelUpgradeInfo.ts

@@ -2,4 +2,8 @@
 
 // This file was generated by [ts-rs](https://github.com/Aleph-Alpha/ts-rs). Do not edit this file manually.
 
-export type ModelUpgradeInfo = { model: string, upgradeCopy: string | null, modelLink: string | null, migrationMarkdown: string | null, };
+export type ModelUpgradeInfo = { model: string, upgradeCopy: string | null, modelLink: string | null, migrationMarkdown: string | null,
+/**
+ * Informational Unix timestamp for this upgrade's scheduled retirement, if known.
+ */
+retirementAt: number | null, };

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

@@ -128,6 +128,9 @@ pub struct ModelUpgradeInfo {
     pub upgrade_copy: Option<String>,
     pub model_link: Option<String>,
     pub migration_markdown: Option<String>,
+    /// Informational Unix timestamp for this upgrade's scheduled retirement, if known.
+    #[ts(type = "number | null")]
+    pub retirement_at: Option<i64>,
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]