feat(ui): add plugin command registry

docs/glossary.md

@@ -22,6 +22,12 @@ FIXME(glossary-completeness): Expand this glossary before the first release so i
 - **goal round** — one continuation cycle admitted for the current goal. The same-session driver materializes a goal round as one goal-sourced [turn](#turn), which can contain multiple steps; unrelated human turns in the same session do not consume the goal-round cap. <a id="goal-round"></a>
 - **goal activation** — process-local permission for a continuation consumer to admit another goal round. Activation is either `armed` or `disarmed`; it is deliberately absent from durable replay, so resume and fork require a later explicit resume mutation before automatic work.
 
+## human command
+
+- **human command** — a slash-prefixed instruction interpreted and executed by a human-facing adapter through `ctx.commands`, without becoming a model message. It is distinct from a model-facing tool and from shell command execution through `ctx.bash`.
+- **command plane** — discovery, parsing, dispatch, cancellation, and result rendering owned by UI adapters and command plugins. Command output is UI state unless the handler separately mutates a durable domain.
+- **command surface** — the adapter identity used to filter definitions, such as `tui` or `acp`; one scoped definition may shadow a same-named global command for its exact agent.
+
 ## loop hierarchy
 
 - **turn** — one drain of admitted input in a session, ending after the model and its tools stop or a terminal policy intervenes. <a id="turn"></a>