## 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
arun eswara
edcec13372