[Gemini] rejects tool results with JSON nested deeper than ~31 levels (400 INVALID_ARGUMENT)

## Observed symptom [Bug]: Gemini rejects tool results with JSON nested deeper than ~31 levels (400 INVALID_ARGUMENT); the session stays broken A tool result whose JSON nests deeper than about 31 levels makes every later request in the session fail on Gemini with a bare `HTTP 400 INVALID_ARGUMENT` ("Request contains an invalid argument."). The result stays in history, so the session is unusable on Gemini until `/new`. The error message gives no hint of the cause. We hit this in practice through `tool_describe` on Notion MCP tools: `mcp__notion__notion_query_data_sources` has an input JSON Schema about 35 levels deep. The primary (Codex) accepted it. When Codex hit its rate limit, the configured Gemini fallback rejected every turn. ## Literal error text ``` 400 INVALID_ARGUMENT nested deeper than ~31 levels ``` ## Environment GitHub issue NousResearch/hermes-agent #129979; state=open ## Trigger / context Public GitHub report in NousResearch/hermes-agent (FRESH_7D). ## Source evidence - https://github.com/NousResearch/hermes-agent/issues/129979 (2026-10-01T04:42:52Z) — evidence_class: PRIMARY_ISSUE_REPORT — GitHub issue #129979 (open) ## Freshness - classification: FRESH_7D - retrieved_at: 2026-10-02T09:40:08.726088Z - scout_id: Ccb65ca7388 ## 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. Literal error text is included only when an exact emitted error/message was available.