Constant CLAUDE_MD_ISOLATION_PLACEHOLDER 

const CLAUDE_MD_ISOLATION_PLACEHOLDER: &str = "<!--\n\
AgentMux: intentionally empty.\n\
\n\
This is an isolated Claude Code config directory (CLAUDE_CONFIG_DIR),\n\
separate from your personal ~/.claude/CLAUDE.md, so this agent never\n\
silently inherits your personal global instructions. To give every\n\
agent shared instructions, use Memory -> Global instead --\n\
those compose into this agent's own project-level CLAUDE.md at launch,\n\
not this file. See SPEC_ISOLATE_HOST_CLAUDE_MD_2026_08_31.md.\n\
-->\n";

Placeholder written by seed_claude_md_placeholder_if_missing — explains itself so an operator who opens the file isn’t confused by an unexplained empty one.