[Bug] Codex Remote Compaction V2 fails with Antigravity Gemini 3.8 Flash

Bug Description

I'm using Codex through 9Router with the Antigravity provider and Gemini 3.8 Flash.

When Codex triggers Remote Compaction V2, the compaction request fails.

Environment

• 9Router: 0.5.65
• Codex: Desktop
• Provider: Antigravity
• Model: ag/gemini-3.8-flash-high
• Also tested with: ag/gemini-3.8-flash-medium
• 9Router API: http://localhost:20128/v1
• Endpoint: /v1/responses

Codex configuration

I'm using a Combo with:

• ag/gemini-3.8-flash-high
• ag/gemini-3.8-flash-medium

Error

When Codex tries to run remote compaction, I get:

Error running remote compact task: unexpected status 503 Service Unavailable:
[antigravity/gemini-3.8-flash-high] [400]: {
  "error": {
    "code": 400,
    "message": "Requests ending with a model turn are not supported"
  }
}