$ sbx kit add m101-demo ./fixtures/kits/env-mixin
Recreating sandbox "m101-demo" to apply augmented kit list...
  Swap container m101-demo-swap-<id> started (id=<sha256>).
Kit "env-mixin" added to sandbox "m101-demo"
[exit 0]

$ sbx exec m101-demo sh -c 'env | grep M101_FROM_KIT'
M101_FROM_KIT=yes
[exit 0]

$ sbx policy ls m101-demo --source kit --wide
SOURCE   CREATED VIA   APPLIES TO          POLICY   POLICY_ID                              RULE            RULE_ID                                TYPE      METHOD   PATH   DECISION   PROTOCOLS   RESOURCES
kit      provisioned   sandbox:m101-demo   -        <uuid>   kit:m101-demo   <uuid>   network   -        -      allow      tcp         example.org
[exit 0]