Four ideas, in the order you'll need them.
Celln has a small vocabulary and it means something specific every time. Start with the model, then the two lanes an executable can run in, then the boundary those lanes are enforced by.
One cell can carry both lanes at once — an attested interpreter and the agent-written file it's fed — the lane is decided per invocation, not once for the whole cell. See the interpreter flag for exactly when that split happens.
1. The model →
Mote, cell, assay, warden, pilot — the five terms and the one lifecycle they describe.
2. Tool lane →
A host-verified tool — a digest-pinned image, a static binary, or a brokered capability — lent read-only into a cell. Where the trust comes from, and how celln run uses it.
3. Agent lane →
Code a model just wrote, sealed and run with narrower authority. Where forging and the laundering ban fit in.
4. The security boundary →
What's hardware-enforced, what's brokered, and what Celln explicitly does not claim.