Extension points¶

Downstream repos extend otto from init modules — ordinary Python modules named in the init list of .otto/settings.toml, imported during bootstrap phase 2 (The command lifecycle). Registration is import-time and side-effect based: an init module calls register_* functions (or applies decorators), and from then on the new component behaves exactly like a built-in — same registries, same CLI listing and completion, same error messages (Registries and the pluggable CLI).

The seams¶

You want to add	Register with	Guide
an `otto run` subcommand	`@instruction()`	otto run
an `otto test` suite	`Test`-prefixed `OttoSuite` subclass (auto-registers)	otto test
a top-level `otto` command	`otto.register_cli_command` / `@otto.cli_command`	Extending the otto CLI
a CLI verb on a host class	`@cli_exposed` on the method	Host capabilities
a host class (new `os_type` base)	`register_host_class`	OS Profiles & Custom Host Classes
an OS profile (defaults bundle)	`register_os_profile` or `[[os_profiles]]` in settings	OS Profiles & Custom Host Classes
a connection (term) backend	`register_term_backend`	Extending otto with custom connection and transfer backends
a file-transfer backend	`register_transfer_backend`	Extending otto with custom connection and transfer backends
a shell dialect	`register_command_frame`	Extending otto for new embedded targets
an embedded binary loader	`register_binary_loader`	Extending otto for new embedded targets
an embedded filesystem type	`register_filesystem`	Extending otto for new embedded targets
a power controller	`register_power_controller`	Extending otto with custom connection and transfer backends
products on hosts	`register_product_provider`	Host capabilities
a host source (lab repository)	`otto.storage.register_lab_repository()`	Host Database
a reservation backend	`register_reservation_backend`	Lab Reservations
per-host monitor parsers	`register_host_parsers`	otto monitor
SNMP metric descriptors	`register_snmp_metric`	otto monitor

Options classes deserve a mention even though they aren’t a registry: a repo-wide @options class shared by instructions and suites is the standard way to give a whole project consistent CLI flags (Options classes).

What keeps third-party code honest¶

Symmetry. Built-ins use the same register_* calls, so the public seams are exercised by otto itself on every run.
Conformance helpers. For contract-shaped seams, otto.testing ships assert_*_conforms functions (e.g. assert_reservation_backend_conforms()) — one pytest test per backend catches every contract violation in one report. otto.examples holds small, copyable reference implementations that otto’s own suite keeps green.
Containment. A broken init module becomes one framed warning, not a broken CLI (The command lifecycle); a name collision is a loud error attributed to both registering modules (Registries and the pluggable CLI).
Schema visibility. Data-side extensions (profiles, preferences, custom settings tables) surface in otto schema export, so editors validate them (Data at the boundary).