SECTOR EXPOSURE CAP (#35) — set (or clear with null) the DESK-level cap on the fraction of the desk's equity ONE sector's open positions may hold, counted across the WHOLE DESK whatever bot opened them. Every bot on the desk obeys it unless the bot sets its own (per-bot wins). Session-owner scoped like the other desk mutations; 404 if the desk is not the caller's (cloak).

A LIVE-FILL knob: the walk refuses a NEW entry whose sector would go over, with its own distinct reason (skipped_sector_cap + a note showing the math), and never touches any verdict. Sector comes from the engine's ONE static map (an unknown symbol is its own "other" bucket); the committed totals are derived fresh every walk through the ONE cost model — nothing is reserved, so closing a position frees its sector's room on the next walk.