Crate fez 

fez: an agent-friendly front end for systemd operations over local and SSH transports.

The crate is structured as a library plus thin binaries so the fake bridge and integration tests can reuse the protocol modules.

Modules

audit

JSON-lines audit logging of attempted and completed mutations. Structured audit for mutations (Section 8, layer 4). Records are written to a pluggable sink; the default writes to the systemd journal via its native protocol over a datagram socket. Selection is via the FEZ_AUDIT env var: unset | “journal” -> journal “off” | “0” -> no-op “file:” -> JSON lines

capabilities

Concrete capability implementations (the commands fez runs). Capability implementations: the concrete commands fez exposes.

capability

Machine-readable descriptors of the capability surface. Machine-readable descriptions of every capability fez exposes, used to advertise the command surface (ids, inputs, flags, examples) to agents.

cli

Command-line argument definitions.

envelope

The fez/v1 JSON response envelope. The fez/v1 JSON response envelope shared by every command’s --json output.

error

Crate-wide error type and exit-code mapping. Crate-wide error type and its mapping to stable codes and exit statuses.

guide

The agent bootstrap contract printed by fez guide. The agent bootstrap contract printed by fez guide. Tells an LLM how to discover and invoke capabilities, what the envelope looks like, what the exit codes mean, and which env vars matter.

mcp

Model Context Protocol server support. A frugal MCP gateway over stdio (Section 6.1): newline-delimited JSON-RPC 2.0 advertising exactly three meta-tools (list_capabilities, describe_capability, invoke) so MCP consumers discover capabilities on demand instead of preloading N tool schemas.

protocol

Wire protocol between fez and the bridge. Wire protocol: framing, message types, and the bridge client.

safety

Guardrails around destructive operations (protected units, confirmations). Pre-flight safety decisions: protected-unit policy and TTY-gated confirmation. Pure functions only — no I/O, no bridge — so the policy is exhaustively testable.

transport

Local and SSH transports for reaching the bridge. Transports that launch the bridge: locally or over SSH.

Functions

run

Entry point: parse-to-exit. Returns the process exit code.