You are defining a porting goal for the Apple platform porting agent.

Pre-flight Check

Locate the agent's artifact directory at <project-root>/.porting/ (defined in porting-methodology). All artifacts live there.

Check if a discovery report exists (discovery-report.md in the artifact directory). If it does not exist, tell the user: "No discovery report found. Run /porting-discover first." and stop.
Check if a previous goal document exists (goal-*.md in the artifact directory). If one exists and is not marked complete, tell the user: "An active porting goal already exists: [goal name]. Complete it before planning a new one, or confirm you want to replace it." Wait for the user's response.

Announce: "Planning next porting goal."

Load Skills

Read these skill files NOW:

porting-methodology — Read skills/porting-methodology/SKILL.md. Understand the porting goal system, milestone lifecycle, and the recommended bring-up order (foundation + rendering milestones).
translating-to-metal4-api — Read skills/translating-to-metal4-api/SKILL.md. Understand the Metal 4 API surface to inform milestone scoping.