Omit temperature for GPT-6 Astra (every request 400s today)

[adambalogh]

The bug

Every GPT-6 Astra chat fails:

Error code: 400 - {'error': {'message': "Unsupported parameter: 'temperature' is not supported with this model.", 'type': 'invalid_request_error', 'param': 'temperature', 'code': None}}

Astra rejects temperature outright — the API 400s if the field is present at all. Clients always send one (chat-app pins temperature: 0.0, and it is part of the signed request hash), so the model has been unusable since it was registered in #153.

Why it slipped through

The gpt-5.6 family has the same restriction and never showed it, because langchain-openai strips temperature itself — but only for model names starting with gpt-5:

>>> ChatOpenAI(model="gpt-5.6-sol", temperature=0.0)._default_params   # no temperature
>>> ChatOpenAI(model="gpt-6-astra", temperature=0.0)._default_params   # temperature: 0.0  ← 400

gpt-6-astra misses that workaround, so the value went out on the wire.

The fix

supports_temperature=False already existed in ModelConfig (for Anthropic's Opus 4.7+ and Fable 5) but was only honored inside the Anthropic branch of get_chat_model_cached. Moved the check up next to force_temperature so the effective temperature is None for any flagged model regardless of provider — every langchain-<provider> package treats None as "omit the field" rather than "send null" — and flagged Astra in the registry.

This keeps the restriction in the registry rather than depending on langchain's model-name heuristics, and covers both request paths (Chat Completions, and the Responses API used when tools are bound).

Tests

tee_gateway/test/test_tee_core.py::TestTemperatureOmission:

• Astra omits temperature on the Chat Completions path and on the Responses API path
• an Anthropic flagged model omits it
• an unflagged model (gpt-4.1) still sends 0.0
• force_temperature (o4-mini) is still applied
• registry-wide sweep: nothing flagged supports_temperature=False can be constructed with a temperature

make lint and the CI test command pass locally (403 passed, 6 skipped, 117 subtests).

Notes

• No client change needed — the gateway is the single choke point for both chat-app's direct OHTTP path and chat-api's SDK path, both of which always send a temperature.
• Registry-only change plus one backend line; no dependency or lockfile change, so nothing here alters PCR inputs beyond the source itself.

🤖 Generated with Claude Code

https://claude.ai/code/session_019GiCnGpGxLEusqVUS6zUHw

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