fix(openai): honour a pinned temperature, warn when dropped; add gpt-6.1-sol

[sroussey]

Problem

finalizeResponsesRequest deleted params.temperature whenever reasoning.effort !== "none". Since unconfigured reasoning models default to effort medium, a caller pinning temperature: 0 had it silently ignored.

Change

• Pinned temperature, no effort configured, GPT-5.6 model (the family verified to accept effort none; class policy and effort_options must allow it): send reasoning.effort: "none" and keep the temperature.
• Every other reasoning model (gpt-6, gpt-6.1, gpt-5.5 and earlier, o-series): the request is not guessed at. The default effort is sent, the temperature is dropped, and a warning is logged once per model and effort (warnTemperatureDroppedOnce).
• gpt-6 never receives none, however the record asks for it.
• Adds gpt-6.1-sol to the fallback model list and pricing (short $2 / cached $0.10 / cache-write $2.50 / output $10; long-context tier derived as 2x/1.5x, which matches the published long row). It resolves to the gpt-6 effort policy (low..max, no none).
• Other OpenAI pricing was compared with the published page and already matched. Nothing else changed.

Tests

Tests are added for gpt-5.6 (kept), gpt-6 and gpt-6.1-sol, gpt-5.5, o3, gpt-4o, and for gpt-6.1-sol pricing and effort policy. 153 tests pass across the 9 affected files. bun run format and bun run format-check are clean and touched no unrelated files.

Not verified

OpenAI's docs page did not state which models reject temperature or top_p, so that behaviour is unchanged for every model except the gpt-5.6 path above.

🤖 Generated with Claude Code

https://claude.ai/code/session_01TzDPzEBWQ9BxV7Pwfo5Db7

[sroussey]

The build check failed at bun install, before any build or test step: the onnxruntime-node postinstall got ETIMEDOUT fetching its binary. That's a runner network failure and doesn't touch this diff. I tried to re-run the failed job but GitHub refused because the run is still in progress, so I'll re-run it once the run completes.

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