Manage swappable operational overlays on top of the central taste corpus. A mode is a small TOML file capturing how *this session's* policy differs from the researcher's stable identity — hardware preferences, budget ceilings, reading focus, scope-lock, subagent model policy, output register, deadlines. The active mode is loaded into every SessionStart alongside taste/INDEX.md. Triggers on `/mode show`, `/mode list`, `/mode switch <name>`, `/mode new <name>`, `/mode edit <name>`, `/mode diff <a> <b>`.
