# K1596–K1600: mount teardown and busy refusal

Each mount has a nonzero volume and generation. Open descriptions, active lookups, and pinned cache pages hold distinct leases. Unmount checks all three lease kinds before changing state. Any remaining lease returns busy and leaves the generation, mounted state, and lease table untouched.

Once every lease is released, unmount advances the generation and marks the mount absent. Remount publishes the new generation. Tokens from before unmount are stale even if the volume number is reused. Lease release is exact and single-use; duplicate release and operations on a stale token are refused without changing state. Generation overflow also refuses unmount without partial teardown.

This fixed three-lease model proves the teardown condition locally. Real filesystem handles, device-backed cache pins, and product release acceptance require separate evidence.