fix(agent): omit sampling params the agent spec never set

[wolfy-j]

Problem

AgentRunner defaulted temperature to 0 whenever a compiled spec omitted it:

temperature = compiled_spec.temperature or AGENT_CONFIG.defaults.temperature,  -- defaults.temperature = 0

CompiledAgentSpec already declared temperature: number?, but the AgentRunner type declared temperature: number, so a caller had no way to express "send no temperature at all".

Claude 4.7+ and Opus/Sonnet 5 reject temperature, top_p and top_k outright. Verified against the live API:

model	temperature	top_p	top_k
claude-opus-5	400	400	400
claude-sonnet-5	400	400	400
claude-haiku-4-5-20251001	accepted	accepted	accepted

$ curl .../v1/messages -d '{"model":"claude-opus-5","temperature":0,...}'
{"type":"error","error":{"message":"`temperature` is deprecated for this model."}}

Anthropic's guidance is to omit these and steer via prompting; adaptive thinking requires the model to control its own sampling. So the fabricated default makes every agent that never asked for a temperature unusable on those models — the flagship and balanced tiers.

Sending temperature: 1 is not an adequate workaround: it is accepted, but it suppresses the model's thinking block (['thinking','text'] becomes ['text']), silently degrading output.

Fix

Stop inventing the default. temperature is dropped from AGENT_CONFIG.defaults, the runner type carries it as number?, and the spec value passes through untouched.

Lua omits a key assigned nil in a table constructor, so the existing options table drops the field on its own once the fabrication stops — no conditional assignment needed.

An explicit temperature, including an explicit 0, is still forwarded. Only "author said nothing" now means "send nothing".

The wippy.llm Claude mapper is deliberately untouched: claude_options.temperature = contract_options.temperature is already nil-transparent, and having the provider strip a value a caller explicitly set would be the mirror-image bug.

Tests

src/agent/test is new — the agent package shipped tests with no harness to run them, mirroring src/llm/test. That gap is why this went unnoticed.

Four cases, all in agent_test.lua:

• spec omits temperature -> runner field is nil and options carries no temperature/top_p/top_k
• spec sets 0.7 -> forwarded as 0.7
• spec sets 0 explicitly -> forwarded as 0, not treated as unset
• the pre-existing "default values for missing fields" case now asserts nil rather than 0

Before the fix: 2 failed / 312. After: 312 passed.