Preserve image generation failure metadata for premium usage limits (#57275)

## Why

Image generation usage-limit errors with the `imagegen_premium` limit ID were not recognized as structured `UsageLimitExceeded` failures.

## What changed

Recognize `imagegen_premium` alongside `image_gen`, preserving the limit ID and available reset time in image generation failure metadata.

## Testing

Extend app-server coverage to verify premium limit metadata and reset-time fallback in completion events, thread reads, and resumed threads. Add unit coverage for missing exhausted-window reset times and unrelated or absent limit IDs.

GitOrigin-RevId: 8cf991776403ddce1f45d9780b8040982fd0fcfe

codex-rs/ext/image-generation/src/tests.rs

@@ -8,8 +8,11 @@ use codex_exec_server::LOCAL_FS;
 use codex_extension_api::ToolOutput;
 use codex_extension_api::ToolPayload;
 use codex_extension_api::ToolSpec;
+use codex_extension_items::image_generation::ImageGenerationFailure;
 use codex_extension_items::image_generation::ImageGenerationInputImage;
 use codex_protocol::ResponseItemId;
+use codex_protocol::error::CodexErr;
+use codex_protocol::error::UsageLimitReachedError;
 use codex_protocol::models::ContentItem;
 use codex_protocol::models::DEFAULT_IMAGE_DETAIL;
 use codex_protocol::models::FunctionCallOutputBody;
@@ -32,6 +35,7 @@ use super::ImagegenArgs;
 use super::PreparedImageRequest;
 use super::imagegen_tool_spec;
 use super::request_for_call_args;
+use super::usage_limit_failure;
 use crate::IMAGE_GEN_NAMESPACE;
 use crate::IMAGEGEN_TOOL_NAME;
 use crate::artifact::image_generation_artifact_path;
@@ -39,6 +43,39 @@ use crate::artifact::image_generation_output_hint;
 
 const RESULT: &str = "cG5n";
 
+#[test]
+fn test_usage_limit_failure_without_an_exhausted_window_reset() {
+    for (limit_id, expected) in [
+        (
+            Some("imagegen_premium"),
+            Some(ImageGenerationFailure::UsageLimitExceeded {
+                limit_id: "imagegen_premium".to_string(),
+                resets_at: None,
+            }),
+        ),
+        (Some("premium"), None),
+        (None, None),
+    ] {
+        let error = CodexErr::UsageLimitReached(UsageLimitReachedError {
+            plan_type: None,
+            resets_at: None,
+            limit_window_minutes: None,
+            rate_limits: Some(Box::new(
+                serde_json::from_value(serde_json::json!({
+                    "limit_id": limit_id,
+                    "primary": {"used_percent": 100.0},
+                    "secondary": {"used_percent": 50.0, "resets_at": 3000}
+                }))
+                .expect("rate limit snapshot"),
+            )),
+            promo_message: None,
+            rate_limit_reached_type: None,
+        });
+
+        assert_eq!(usage_limit_failure(&error), expected);
+    }
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn referenced_files_record_the_exact_bytes_read_for_each_request() {
     let directory = tempfile::tempdir().expect("temporary directory");

codex-rs/ext/image-generation/src/tool.rs

@@ -323,7 +323,7 @@ fn usage_limit_failure(error: &CodexErr) -> Option<ImageGenerationFailure> {
     };
     let rate_limits = usage_limit.rate_limits.as_deref()?;
     let limit_id = rate_limits.limit_id.as_deref()?;
-    if limit_id != "image_gen" {
+    if !matches!(limit_id, "image_gen" | "imagegen_premium") {
         return None;
     }