[c13 follow-up] Agent-mode UUID/ISO-8601 transforms data-lossy on user text

[ohdearquant]

Codex round-1 MAJ-2 on PR #384. presentation.rs Agent mode shortens any 36-char hex+dash substring it sees, including inside content/description fields. Should be key-aware (only transform fields with names like 'id', 'created_at', etc.).