Extends scripts/check-agent-docs-drift.sh to catch a second class of
agent-doc drift: per-tool subdirectory duplicates introduced by an
earlier 'centralize AI agent documentation references' refactor.
The refactor (visible in learning_ai_clock origin/main, commit c73fda7)
created .claude/AGENTS.md, .cline/AGENTS.md, .cursor/AGENTS.md as 1-line
redirect pointers, plus .devin/AGENTS.md (218 lines) and .devin/CONTEXT.md
(206 lines) with full duplicate documentation. All five duplicate the
canonical repo-root AGENTS.md.
The drift check now exits 1 if any of those five paths exist in any
repo listed in repos.txt. Also renumber comment markers (was 1..5,
now 1..6) and update the header comment.
Verified: bash scripts/check-agent-docs-drift.sh exits 0 with
'17 repos in sync' across the ecosystem.