LemonGateway.
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Registry of available AI engine modules.
Maintains a mapping of engine ID strings to their implementing modules. Validates engine IDs on registration and provides lookup and resume token extraction across all registered engines.
The built-in engines are the CLI wrappers this app ships. Engines that live
in another application register themselves at boot with register/1 — that
is how coding_agent contributes the "lemon" engine without the gateway
depending on it. Registration also updates :lemon_gateway, :engines, so a
registry restart keeps the engine.
What gets written back is the union of the configured list and the runtime
registrations, not the set this process is currently serving. Those differ: a
configured engine whose module is not loadable yet is skipped for lookups but
stays in the configuration, because "not loadable at boot" is a statement
about start order, not about intent. Persisting the serving set instead would
let one unrelated register/1 delete an engine the operator configured.
An engine is third-party code called from inside this process, so every call
into one — LemonGateway.Engine.id/0 and
LemonGateway.Engine.extract_resume/1 — is isolated. An engine that raises
is logged and skipped rather than taking the registry (and, through the
supervisor's restart intensity, the gateway) down with it.
Summary
Functions
Returns a specification to start this module under a supervisor.
Iterates all registered engines and calls extract_resume/1 on each until one returns
a non-nil ResumeToken. Returns {:ok, token} if found, :none otherwise.
Returns the engine module for the given ID, or nil if not registered.
Returns the engine module for the given ID, or raises if not found.
Returns a list of all registered engine IDs.
Registers an engine module at runtime.
Types
Functions
Returns a specification to start this module under a supervisor.
See Supervisor.
@spec extract_resume(String.t()) :: {:ok, LemonCore.ResumeToken.t()} | :none
Iterates all registered engines and calls extract_resume/1 on each until one returns
a non-nil ResumeToken. Returns {:ok, token} if found, :none otherwise.
@spec get_engine(engine_id()) :: engine_mod() | nil
Returns the engine module for the given ID, or nil if not registered.
@spec get_engine!(engine_id()) :: engine_mod()
Returns the engine module for the given ID, or raises if not found.
@spec list_engines() :: [engine_id()]
Returns a list of all registered engine IDs.
@spec register(engine_mod()) :: :ok | {:error, term()}
Registers an engine module at runtime.
Idempotent: registering the same module again is a no-op, and re-registering
an id with a different module replaces it. Returns {:error, :unavailable}
when the registry is not running, so a caller booting outside the gateway
runtime does not crash.