CLAUDE.md: delegate implementation once the design is settled

Added by Andy: design, review and any flagged decision stay with the
session; the file edits go to the sonnet-implementer subagent.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EFMUNbw2UpRPmgsqviAowb

Author: andy

CLAUDE.md

@@ -9,6 +9,8 @@ lean map of where things live and what to watch out for — it is
 intentionally *not* a running log of past sessions. For that, see
 "Where the history lives" at the bottom.
 
+Once a design decision is settled, delegate the implementation to the sonnet-implementer subagent rather than writing the files yourself. Keep doing the design work, review, and any decision the subagent flags, directly.
+
 ## Standing preferences
 - Andy runs Debian ("trixie") on his machines — **beryllium** and
   **niobium**. Default to Debian conventions, not Ubuntu, for anything