Mission Run Overview
Mission Run: Merge Honors Mission Retention Policy
Make spec-kitty merge honor a mission's branch/worktree retention policy instead of silently deleting them.
P1 data-loss bug #3131: spec-kitty merge applies its default branch/worktree cleanup even when a mission explicitly requires retaining lane branches and worktrees, deleting them with no operator-visible warning. This mission persists a machine-readable retention policy in mission metadata, makes merge fail closed (retain + warn) when the default conflicts with it, and requires an explicit operator override to delete.