Send temperature through extra_body; check kwargs against SDK signatures

[drewOrc]

The first make llm-smoke after #14 failed on every call before any request was sent: TypeError: Messages.create() got an unexpected keyword argument 'temperature'. Nothing reached the API, US$0 was spent, and no key appeared in the output.

Cause

anthropic 1.x removed temperature, top_p and top_k from messages.create(). The API did not remove them, and Haiku 4.5 still accepts them. The runner's tests use a fake client that accepts any keyword, so none of them could see the mismatch with the real SDK.

Fix

• request_params sends extra_body={"temperature": 0.0}. The SDK merges extra_body into the request JSON as is, which is the SDK upgrade guide's advice when the model still accepts the setting and the code depends on it. Temperature 0 is part of the comparison with cost-aware-hybrid-router, so it is moved, not dropped.
• The identity still records temperature 0, so its hash is unchanged. The failed rows in the smoke journal are retried on the next run.
• count_tokens only ever sent model, system and messages, so it was not affected. Its arguments now come from count_tokens_params(), the one place they are built, as request_params() is for messages.create.

New tests (for the 2026-09-29 smoke incident)

• test_the_arguments_we_send_fit_the_installed_sdk_signatures binds the kwargs from request_params() and count_tokens_params() to the installed SDK's Messages.create and Messages.count_tokens signatures. It needs no network and no key.
• test_the_fake_client_receives_exactly_the_built_arguments checks that what the client receives is exactly those kwargs. The signature check therefore covers what is actually sent.
• test_request_matches_the_old_project_settings now asserts extra_body["temperature"] == 0.0 and that no top-level temperature is sent.

Mutation check (backup and restore): 6 mutations, all caught:

• temperature at the top level (also the original bug)
• temperature dropped
• temperature added to count_tokens
• classify or count_tokens sending extra kwargs of their own

make lint, make test (423 passed) and make smoke pass locally.