Add an LLM steering brain behind the DecidePort seam

[xmap]

Summary

• Adds LlmDecidePort, a fifth DecidePort substrate that asks an LLM for the next autonomous-experiment action (Measure a next point, or Stop) from the full SteeringEvidence. The DecidePort docstring already named an LLM as an intended brain and the LLM port named a Strategy consumer; this fills that seam.
• Purely additive: no new aggregate, agent seed, or subscriber, so it does not touch the agent-subscriber Reaction-widening trigger.
• Homed in cora.operation.adapters (not cora.agent.prompts) because tach forbids cora.operation -> cora.agent; consumes only the LLM port + shared steering value types.

Design

• Stateless (full evidence handed over each call, fit for replay).
• Translates the LLMError family into the Decide*Error taxonomy the conduct loop already folds into a deferred steering decision (never crashes the loop).
• Guards against a hallucinated next_point naming an axis outside the SteeringSpace; SteeringAdvice self-validation catches a malformed verdict/point pairing and out-of-range confidence.
• Evidence serialized via canonical_json_bytes so the prompt-cache prefix stays byte-stable across write/replay.
• Wired as the llm substrate in build_decide_port via an injected llm port (ValueError when absent, mirroring the bo-missing guard); both conduct_until_advised handlers pass deps.llm through.

Scope (Stage 0)

• Kept OFF the wire (WireDecideSubstrate unchanged) and NOT yet the ExperimentSteerer default; those are deliberate later stages.

Test plan

• 15 new unit tests (test_llm_decide_port.py): Measure/Stop, full-error-mapping table, unknown verdict, Measure-without-point, hallucinated-axis guard, factory arm + llm-required guard.
• Full operation unit slice green (1170 passed).
• Architecture/tach green (proves operation -> infrastructure.ports.llm import legal + decide-port purity holds + canonical-json single-source rule).
• pyright + ruff clean.
• End-to-end drive through build_decide_port(..., llm=FakeLLM()) + advise_next.

🤖 Generated with Claude Code

[github-actions]

Coverage report

Click to see where and how coverage changed

File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
apps/api/src/cora/operation/adapters
_llm_decide_prompt.py
decide_port_config.py
llm_decide_port.py
apps/api/src/cora/operation/features/conduct_until_advised
handler.py
apps/api/src/cora/operation/features/conduct_until_advised_from
handler.py
apps/api/src/cora/operation/ports
decide_port.py
Project Total

This report was generated by python-coverage-comment-action