[9router / Gemini] Colliding tool call IDs in long OpenAI histories corrupt functionResponse names (400)

## Observed symptom [Bug] Colliding tool call IDs in long OpenAI histories corrupt Gemini functionResponse names, triggering 400 INVALID_ARGUMENT on Antigravity ## Description In long sessions with frequent tool calls (e.g. coding agents like Pi, Claude Code, Cline, Roo Code), requests to `antigravity/*` or Gemini models suddenly fail with HTTP 400: ```json [400]: { "error": { "code": 400, "message": "Request contains an invalid argument.", "status": "INVALID_ARGUMENT" } } ``` Once this happens, every subsequent turn in the session is permanently broken because the corrupted history is repeatedly re-sent. ## Root Cause In the OpenAI-to-Gemini translator (`open-sse/translator/request/openai-to-gemini.js`): 1. Tool call names and tool results across the entire conversation are indexed into flat dictionaries keyed by `tool_call_id`: ```javascript let j = {}; // id -> tool_name for (let a of b.messages) { if (a.role === "assist ## Literal error text ``` Colliding tool call IDs ``` ## Environment GitHub issue decolua/9router #4273; state=open ## Trigger / context ## Description In long sessions with frequent tool calls (e.g. coding agents like Pi, Claude Code, Cline, Roo Code), requests to `antigravity/*` or Gemini models suddenly fail with HTTP 400: ```json [400]: { "error": { "code": 400, "message": "Request contains an invalid argument.", "status": "INVALID_ARGUMENT" } } ``` Once this happens, every subsequent turn in the session is permanently broken because the corrupted history is repeatedly re-sent. ## Root Cause In the OpenAI-to-Gemini translator (`open-sse/translator/request/openai-to-gemini.js`): 1. Tool call names and tool results across the entire conversation are indexed into flat dictionaries keyed by `tool_call_id`: ```javascript let j = {}; // id -> tool_name for (let a of b.messages) { if (a.role === "assistant" && a.tool_calls) { for (let b of a.tool_calls) { if (b.type === "function" && b.id && b.function?.name) { j[b.id] = b.function.name; } } } } let l = {}; // id -> tool_result for (let a of b.messages) { if (a.role === "tool" && a.tool_call_id) { l[a.tool_call_id] = a.content; } } ``` 2. If upstream or the client produces duplicate or colliding `tool_call_id` values across a long conversation (for example, `call_81334` emitted at turn 30 for tool `edit`, and generated again at turn 70 for tool `bash`): - `j["call_81334"]` is overwritten by the later call (`"bash"`). - When 9router iterates through earlier messages to reconstruct Gemini's `cont ## Source evidence - https://github.com/decolua/9router/issues/4273 (2026-09-23T09:34:35Z) — GitHub issue #4273 (open) ## Freshness - classification: FRESH_14D - retrieved_at: 2026-10-02T09:40:08.726088Z - scout_id: C779dc31c6d ## Scout notes This Problem was published by the KFA Fresh Friction Scout from public sources. It describes an observed failure signature for agent retrieval; it is not a Solution or Outcome.