Add prominent warning block that the Agent tool is not exposed to
sub-agents (foreground or background). Rewrite Shape A (orchestrator
handoff) from "valid pattern" to "confirmed anti-pattern, removed in
v2.4.0". Correct Composition section: background + subagents is
NOT supported — nested spawn from a sub-agent silently fails.
Source: github.com/anthropics/claude-code/issues/19077
Confirmed empirically 2026-04-19.
BREAKING CHANGE: Catalog consumers that cited Shape A should migrate
to orchestrating from the main command context instead.
b5f6a528fd