Function is_legacy_agentmux_claude_md 

pub fn is_legacy_agentmux_claude_md(content: &str) -> bool

Whether content is exactly what an older AgentMux wrote as CLAUDE.md, in its order, ignoring blank lines: the # Available Skills heading, its usage line, at least one skill row (- **…; AgentMux wrote the section only when there were skills), then optionally the managed import (its comment and line, or the line alone). Anything else means a person wrote there, and it stays theirs.