teardown
Giving an agent a shell is not the same as giving it a tool
A general shell exposes ambient authority, while a narrow tool makes scope, auditability, and verification part of the interface.
A shell is convenient because it can eventually perform almost any operation. That convenience is also the abstraction leak: scope, credentials, side effects, audit trails, and rollback are left implicit in a command string.
A narrow tool makes those concerns visible. Its inputs can describe a resource and an intended operation; policy can decide whether that operation is allowed; the runtime can constrain and record it; a verifier can observe the result. Sandboxing and short-lived credentials can still matter, but they have a clear boundary to protect.
This is a conceptual teardown of the interface choice, not a hands-on report. It does not claim a specific shell experiment, installable SDK, or tested environment. The boundary is explored further in Authority Compiler and Long-Horizon Verification.