GitHub Copilot CLI plan mode is specifically designed for situations in which an implementation strategy must be developed and reviewed before code modifications begin. In plan mode, Copilot can inspect and analyze the repository, ask clarifying questions, and construct a structured implementation plan while protecting project files from normal editing operations. The resulting plan can then be reviewed and approved before Copilot proceeds with implementation. GitHub explicitly describes plan mode as a mechanism for identifying misunderstandings before code is written and maintaining human control over complex, multi-step work.
Option A is incorrect because --agent=AGENT selects a custom agent; it does not establish a planning-and-approval phase. Option B is the opposite of the requirement: --allow-all grants Copilot broad permission to use tools, paths, and URLs without individual approval. Option D is also incorrect because /compact relates to managing conversation/context size rather than establishing an implementation plan.
Therefore, switching to plan mode is the appropriate first action when the development process requires human review and agreement before changes are applied.
Study Guide Reference Topics: Prepare agent architecture and SDLC processes; human-in-the-loop development; planning before implementation; controlled agent execution.