Expose image generation usage-limit failures (#38024)

## What changed

- Add structured `usageLimitExceeded` metadata to failed image-generation
  items, including the image limit ID and optional reset timestamp.
- Preserve the failure metadata in completion events, app-server thread
  history, thread reads and resumes, and migrated legacy rollouts.
- Export the new failure type in the generated JSON and TypeScript schemas.

## Testing

- Cover usage-limit responses through item completion, persistence, and thread
  resume.
- Verify legacy rollout migration retains image-generation failure metadata.

GitOrigin-RevId: 91c31a2a47456b6b916ee03002ff314b05946dd4

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

@@ -863,6 +863,7 @@ impl ThreadHistoryBuilder {
             revised_prompt: None,
             result: String::new(),
             transparent_background: None,
+            failure: None,
             saved_path: None,
         });
         self.upsert_item_in_current_turn(item);
@@ -875,6 +876,7 @@ impl ThreadHistoryBuilder {
             revised_prompt: payload.revised_prompt.clone(),
             result: payload.result.clone(),
             transparent_background: payload.transparent_background,
+            failure: payload.failure.clone(),
             saved_path: payload.saved_path.clone(),
         });
         self.upsert_item_in_current_turn(item);
@@ -2079,6 +2081,7 @@ mod tests {
                         revised_prompt: Some("A blue square".to_string()),
                         result: "cG5n".to_string(),
                         transparent_background: Some(true),
+                        failure: None,
                         saved_path: Some(saved_path.clone()),
                     },
                 )),
@@ -2110,6 +2113,7 @@ mod tests {
                 revised_prompt: Some("A blue square".to_string()),
                 result: "cG5n".to_string(),
                 transparent_background: Some(true),
+                failure: None,
                 saved_path: Some(saved_path),
             })]
         );
@@ -2373,6 +2377,12 @@ mod tests {
                 revised_prompt: Some("final prompt".into()),
                 result: "Zm9v".into(),
                 transparent_background: Some(true),
+                failure: Some(
+                    codex_extension_items::image_generation::ImageGenerationFailure::UsageLimitExceeded {
+                        limit_id: "image_gen".into(),
+                        resets_at: Some(1_786_150_800),
+                    },
+                ),
                 saved_path: Some(test_path_buf("/tmp/ig_123.png").abs()),
             })),
             RolloutItem::EventMsg(EventMsg::TurnComplete(TurnCompleteEvent {
@@ -2413,6 +2423,12 @@ mod tests {
                         revised_prompt: Some("final prompt".into()),
                         result: "Zm9v".into(),
                         transparent_background: Some(true),
+                        failure: Some(
+                            codex_extension_items::image_generation::ImageGenerationFailure::UsageLimitExceeded {
+                                limit_id: "image_gen".into(),
+                                resets_at: Some(1_786_150_800),
+                            },
+                        ),
                         saved_path: Some(test_path_buf("/tmp/ig_123.png").abs()),
                     }),
                 ],

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

@@ -15,6 +15,7 @@ use crate::protocol::item_builders::convert_patch_changes;
 use crate::protocol::item_builders::review_output_text;
 use codex_experimental_api_macros::ExperimentalApi;
 use codex_extension_items::ExtensionItem;
+pub use codex_extension_items::image_generation::ImageGenerationFailure;
 pub use codex_extension_items::image_generation::ImageGenerationItem;
 pub use codex_extension_items::sleep::SleepItem;
 pub use codex_extension_items::web_search::WebSearchAction;
@@ -929,6 +930,7 @@ impl From<CoreTurnItem> for ThreadItem {
                     revised_prompt: image.revised_prompt,
                     result: image.result,
                     transparent_background: None,
+                    failure: None,
                     saved_path: image.saved_path,
                 })
             }