Sub-Agent Delegation Rules

Platform-agnostic. The context-loss problem is the same on Claude Code and Copilot.

The universal rule

• Sub-agents / extensions / participants start with FRESH context. They do NOT inherit parent's skills, history, or accumulated state.
• Pass skills explicitly — every platform, every time.
• Validate the handoff. First sub-agent action: echo received skills. Fail loudly on mismatch.

Claude Code

• Inherit: CLAUDE.md, tool definitions, MCP servers.
• Pass skills: AgentDefinition(skills=[...]) or inline in Task tool prompt.
• context: fork is INVERTED (GH #20492) — creates blank, not copy.
• AskUserQuestion unavailable in sub-agents (GH #34592).

VS Code Copilot

• Agent mode persists within session BUT terminal commands and chat participants get fresh context.
• Scripts the agent writes that spawn sub-processes inherit NOTHING from Copilot.
• Pass skills: #file:path/to/SKILL.md in chat, or .github/copilot-instructions.md for always-on.

Cross-platform ground truth