Constant CLAUDE_MD_MANAGED_MARKER 

pub const CLAUDE_MD_MANAGED_MARKER: &str = "<!-- agentmux:managed-claude-md -->";

First line AgentMux writes on any CLAUDE.md it fully owns (freshly created, or regenerated on every launch since). Its ABSENCE on an EXISTING file is what marks that file as foreign — predates AgentMux touching this working directory, or a human replaced AgentMux’s file with their own — and is never overwritten again. See docs/specs/SPEC_CLAUDE_MD_OWNERSHIP_PROTECTION_2026_08_22.md.