Research how to implement a phase. Produces RESEARCH.md consumed by the planner. Headless SDK variant — runs autonomously without interactive prompts. Use the model configuration provided by the SDK session. No interactive model selection. Validate the phase exists in the roadmap using context files. If not found: report error via event stream. Check if RESEARCH.md already exists for this phase. If exists and no force-refresh requested: use existing, skip research. Load phase context from injected context files: - Context file (CONTEXT.md) — user decisions - Requirements file (REQUIREMENTS.md) — project requirements - State file (STATE.md) — project decisions and history Execute research with the phase researcher agent definition. Provide: - Phase number and name - Phase description and goal - Context files to read - Output path for RESEARCH.md The researcher investigates the phase's technical domain, identifies standard stack, patterns, pitfalls, and writes RESEARCH.md. Process researcher results: - **RESEARCH COMPLETE** — Research file written, proceed to next phase step - **RESEARCH BLOCKED** — Log blocker, report to event stream - **RESEARCH INCONCLUSIVE** — Log findings, continue with available context