diff --git a/packages/plugin/src/effect/command.ts b/packages/plugin/src/effect/command.ts
index 59be027df91..ce40ff193d1 100644
--- a/packages/plugin/src/effect/command.ts
+++ b/packages/plugin/src/effect/command.ts
@@ -1,16 +1,19 @@
 import type { CommandApi } from "@opencode-ai/client/effect/api"
-import type { CommandInfo } from "@opencode-ai/client"
-import type { Effect } from "effect"
-import type { Transform } from "./registration.js"
+import type { Session } from "@opencode-ai/schema/session"
+import type { Effect, Scope } from "effect"
+import type { Registration } from "./registration.js"
 
-export interface CommandDraft {
-  list(): readonly CommandInfo[]
-  get(name: string): CommandInfo | undefined
-  update(name: string, update: (command: CommandInfo) => void): void
-  remove(name: string): void
+export interface CommandInvocation {
+  readonly sessionID: Session.ID
+  readonly arguments: string
 }
 
-export interface CommandDomain extends CommandApi<unknown> {
-  readonly transform: Transform<CommandDraft>
-  readonly reload: () => Effect.Effect<void>
+export interface CommandDefinition {
+  readonly name: string
+  readonly description?: string
+  readonly run: (input: CommandInvocation) => Effect.Effect<void>
+}
+
+export interface CommandDomain extends Pick<CommandApi<unknown>, "list"> {
+  readonly register: (definition: CommandDefinition) => Effect.Effect<Registration, never, Scope.Scope>
 }
diff --git a/packages/plugin/src/promise/command.ts b/packages/plugin/src/promise/command.ts
index cc9de3f3cb9..30c879703a8 100644
--- a/packages/plugin/src/promise/command.ts
+++ b/packages/plugin/src/promise/command.ts
@@ -1,15 +1,18 @@
 import type { CommandApi } from "@opencode-ai/client/promise/api"
-import type { CommandInfo } from "@opencode-ai/client"
-import type { Transform } from "./registration.js"
+import type { Session } from "@opencode-ai/schema/session"
+import type { Registration } from "./registration.js"
 
-export interface CommandDraft {
-  list(): readonly CommandInfo[]
-  get(name: string): CommandInfo | undefined
-  update(name: string, update: (command: CommandInfo) => void): void
-  remove(name: string): void
+export interface CommandInvocation {
+  readonly sessionID: Session.ID
+  readonly arguments: string
 }
 
-export interface CommandDomain extends CommandApi {
-  readonly transform: Transform<CommandDraft>
-  readonly reload: () => Promise<void>
+export interface CommandDefinition {
+  readonly name: string
+  readonly description?: string
+  readonly run: (input: CommandInvocation) => Promise<void>
+}
+
+export interface CommandDomain extends Pick<CommandApi, "list"> {
+  readonly register: (definition: CommandDefinition) => Promise<Registration>
 }