* feat(claude_code_exec): add claude code optimizer backend with SDK trace support
Register claude_code_exec as a full optimizer/target backend (issue #233).
--backend claude_code_exec now defaults both roles to claude_code_exec so
reflection sees the agent's complete session, and the SDK message stream is
parsed into structured trace steps persisted as claude_trace_steps.txt and
injected into the analyst prompt.
- model/claude_code_backend.py (new): chat_optimizer/chat_optimizer_messages on
run_claude_code_chat, reasoning_effort threaded through, retry loop that
surfaces non-JSON structured replies as RuntimeError, token tracking.
- model/codex_harness.py: parse/format/persist claude trace steps (text,
tool_call, tool_result; drops init/thinking_tokens; 200-char tool_result cap;
total truncation) + effort override on run_claude_code_chat.
- trainer.py/reflect.py: inject Claude Trace Steps gated behind
REFLACT_CLAUDE_TRACE_TO_OPTIMIZER, set by the trainer only for claude_code_exec
targets with model.claude_trace_to_optimizer (mirrors codex gate; default true).
- config.py/default.yaml/docs: model.claude_trace_to_optimizer key + flatten
mapping + config.md rows.
- backend_config.py + model/__init__.py: register backend, route chat dispatch,
token summary, reasoning effort, deployments.
- scripts/train.py, eval_only.py: symmetric default + accurate comments.
- tests: tests/test_claude_code_backend.py (10 tests: parsing, dispatch, effort,
retry, trainer/reflect gating); test_role_backend_resolution.py updated to the
symmetric default.
Verified: 58 unit tests pass; integration smoke on searchqa improved best-on-val
0.7500 -> 0.9375 with 80 claude_trace_steps.txt written; all output files valid
UTF-8 (no GBK mojibake).
* fix(claude_code_exec): address #233 review feedback
Nuplum
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