planner-orchestration

# Single-Session Orchestration The user-started primary conversation owns durable artifacts, integration judgment, and user communication. Platform-provided explorers and other predefined subagents may continue to serve the harness's normal investigation workflow. This skill governs planned implementation delegation, not the platform's general exploration behavior. ## Model Checkpoints The user, not the harness, selects the model. Keep each phase in the primary conversation so the active model, transcript, and costs are visible in one place. 1. **Design checkpoint — strong model.** Use the user's strong model for clarification, codebase investigation, specs, plans, task decomposition, and high-risk design decisions. Default Codex guidance is GPT-5.6 Sol/high. 2. **Implementation checkpoint — user switch.** Once the spec, plan, and task files are ready, summarize their paths and ask the user to switch the main session to the lower-cost implementation model. Default Codex guidance is GPT-5.6 Terra/medium. Do not silently continue on the strong model when the user has asked for a cost-controlled workflow. 3. **Execution checkpoint — lower-cost model.** In the same conversation, read the approved task file, mark it `in_progress`, implement with `/tdd`, run its exact targeted checks, and mark it `done`. Work sequentially through the plan by default. 4. **Escalation checkpoint.** Stop and ask the user to switch back to a stronger model before an ar...