sub2api/openspec/changes/image-generation-concurrency-isolation/tasks.md

1. Spec and documentation

• 1.1 Create OpenSpec proposal, design, tasks, and capability spec for image concurrency isolation.
• 1.2 Add a local 2ue note for the external image gateway deployment pattern and current non-goals.

2. Config

• 2.1 Add gateway.image_concurrency.enabled and gateway.image_concurrency.max_concurrent_requests config fields.
• 2.2 Register defaults that keep existing behavior unchanged.
• 2.3 Validate max concurrent requests as non-negative.
• 2.4 Update deploy/config.example.yaml with safe usage notes.
• 2.5 Add image concurrency overflow mode, wait timeout, and max waiting request config.

3. Runtime limiter

• 3.1 Implement a process-level image concurrency limiter with resize-on-config-read behavior.
• 3.2 Acquire/release the limiter around /v1/images/generations and /v1/images/edits before account scheduling.
• 3.3 Acquire/release the limiter around explicit /v1/responses image generation intent before account scheduling.
• 3.4 Ensure limiter rejections return 429 rate_limit_error and do not trigger account failover.
• 3.5 Support reject and wait overflow modes with bounded wait timeout and waiting queue size.

4. Tests and verification

• 4.1 Add config default and validation tests.
• 4.2 Add handler tests for image endpoint limiter rejection.
• 4.3 Add handler tests proving text-only Responses requests are not rejected by the image limiter.
• 4.4 Run focused Go tests for config and OpenAI handler/service paths.
• 4.5 Add limiter tests for wait success, wait timeout, and waiting queue overflow.