The planner and worker user messages now carry worker output, finding
details, recent_facts, finding_list, cold_digests, related_tasks and hints
not written by the operator inside a code-owned data envelope whose nonce
comes from crypto/rand (16 bytes, hex) once per message. Embedded marker
stems are neutralised with a fixed-string replacement. The task goal, goal
nodes, constraints and the operator's own hints stay outside, labelled
operator. Overview fact summaries are capped at factSummaryMax (160 runes),
the cap list_facts already uses.
