Module registry 

ModeRegistry: register modes, look them up, drive activation / deactivation against a per-buffer ActiveModes and an App-owned GuardStoreHandle.

M-async.3: activation is spawn-based with sequential cascade. The sync prefix walks the requested mode + its implies() tree, validates each, mutates active_modes for each, and builds an ordered cascade plan (Vec<CascadeStep>). One task is spawned that walks the plan in DFS order, awaiting each step’s on_activate.await before moving to the next. This guarantees a parent’s lifecycle resolves before its implied children’s begin – no sub-mode reads parent’s not-yet-written state.

On lifecycle error the spawned task publishes ModeActivationFailed for the failing step, then publishes ModeActivationFailed { reason: "cascade aborted by X" } for every remaining (unrun) step. An App-side subscriber (drain_mode_lifecycle_events) rolls back active_modes / mode_guards on each.

Deactivation stays synchronous (Drop is sync): the dispatcher locks the store, removes the Guard, drops it. The MajorExiting / MinorDeactivated event publishes before the drop fires.

Validation order before spawning:

1. Mode is registered (ModeActivationError::NotRegistered).
2. Mode kind matches the call (WrongKind).
3. Buffer satisfies required capabilities (MissingCapability).
4. No conflict with already-active modes (Conflict).
5. All implies dependencies are registered (UnregisteredDependency).

Lifecycle errors (from on_activate.await) become ModeActivationFailed events on the bus; the spawned task never returns them to the caller (the caller already returned Ok(())).

Structs

ModeRegistry

Mode registry. Owns the catalogue of registered modes (Arc<dyn DynMode>) and drives activation / deactivation.

Enums

RegistrationError

Why a registration failed.

Type Aliases

ModeRegistryHandle

The runtime-mutable mode-registry handle the editor holds and shares as a service. ArcSwap gives wait-free reads on the keymap-resolution / mode-activation paths and copy-on-write RCU writes for runtime mode registration (a mode plugin loaded via :plugin-load, PL8.B). Reads take a snapshot (load/load_full); a mode load/unload clones-mutates-stores a fresh registry. The plugin loader reaches this via service::<ModeRegistryHandle>().