fix(codex): retain worktree context across turns - #260

The change looks sound. The two earlier findings are resolved: the new tests construct worktree reports as JSON fixtures rather than shelling out to git, and the unregistered_worktree_does_not_update_the_app_server_workspace and mismatched_worktree_branch_does_not_update_the_app_server_workspace tests exercise the registration-rejection paths. The helpers and assertions are internally consistent, tempdir-based filesystem setup is deterministic and offline, and I see no new bugs introduced by this diff. Code retrieval was unavailable (model: openrouter embeddings returned 404 Not Found: {"error":{"message":"No allowed providers are available for the selected model. Providers serving openai/text-embedding-3-small: openai, azure, but your account's allowed-providers setting permits only: deepinfra, streamlake, digitalocean. To change your allowed providers, visit: https://openrouter.ai/settings/privacy.","code":404,"metadata":{"available_providers":["openai","azure"],"requested_pro), so this review saw the diff alone.

No findings.

Fixed since the last review

• Do not shell out to real git in unit tests
• Exercise the is_registered_worktree rejection path