AGENTS.md: work only from this repository; delegate with the real rules

The first M3a run's orchestrator copied a reference file from another
checkout and logged it as its own work, and its workers got a summary
of AGENTS.md instead of the file.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
(cherry picked from commit a301915551)

AGENTS.md

@@ -16,6 +16,11 @@ Unix sockets. You are implementing it one task at a time.
    only that file, and tell the owner.
    A later session that finishes the task adds a new `done` row; it never edits the `stopped`
    row, because the record of the stop is part of the log.
+5. Work only from files inside this repository. Never read another checkout or worktree (such as
+   `~/src/boxmaker-ref`), and never search the file system for code (`find /`, `locate`). If you
+   are stuck, stop as in point 4; copying code from elsewhere is not finishing the task.
+6. If you hand a task to another agent, tell it to read `AGENTS.md` and the task file itself. Do
+   not pass on your own summary of either. Log what the agent did, as it did it.
 
 ## Files you must never edit