diff --git a/packages/opencode/specs/effect-migration.md b/packages/opencode/specs/effect-migration.md
index 4f195917fde2..6180fe0932f7 100644
--- a/packages/opencode/specs/effect-migration.md
+++ b/packages/opencode/specs/effect-migration.md
@@ -132,7 +132,7 @@ Still open and likely worth migrating:
 - [ ] `Worktree`
 - [ ] `Installation`
 - [ ] `Bus`
-- [ ] `Command`
+- [x] `Command`
 - [ ] `Config`
 - [ ] `Session`
 - [ ] `SessionProcessor`
diff --git a/packages/opencode/src/bus/bus-event.ts b/packages/opencode/src/bus/bus-event.ts
index 7fe13833c862..1d9a31d4a271 100644
--- a/packages/opencode/src/bus/bus-event.ts
+++ b/packages/opencode/src/bus/bus-event.ts
@@ -1,5 +1,5 @@
 import z from "zod"
-import type { ZodType } from "zod"
+import type { ZodObject, ZodRawShape } from "zod"
 import { Log } from "../util/log"
 
 export namespace BusEvent {
@@ -9,7 +9,7 @@ export namespace BusEvent {
 
   const registry = new Map<string, Definition>()
 
-  export function define<Type extends string, Properties extends ZodType>(type: Type, properties: Properties) {
+  export function define<Type extends string, Properties extends ZodObject<ZodRawShape>>(type: Type, properties: Properties) {
     const result = {
       type,
       properties,
diff --git a/packages/opencode/src/bus/global.ts b/packages/opencode/src/bus/global.ts
index 43386dd6b20f..dcc7664007e4 100644
--- a/packages/opencode/src/bus/global.ts
+++ b/packages/opencode/src/bus/global.ts
@@ -4,7 +4,7 @@ export const GlobalBus = new EventEmitter<{
   event: [
     {
       directory?: string
-      payload: any
+      payload: { type: string; properties: Record<string, unknown> }
     },
   ]
 }>()
diff --git a/packages/opencode/src/command/index.ts b/packages/opencode/src/command/index.ts
index 2c47984fdd8f..3ef6974f0947 100644
--- a/packages/opencode/src/command/index.ts
+++ b/packages/opencode/src/command/index.ts
@@ -1,15 +1,18 @@
 import { BusEvent } from "@/bus/bus-event"
+import { InstanceContext } from "@/effect/instance-context"
+import { runPromiseInstance } from "@/effect/runtime"
 import { SessionID, MessageID } from "@/session/schema"
+import { Effect, Fiber, Layer, ServiceMap } from "effect"
 import z from "zod"
 import { Config } from "../config/config"
-import { Instance } from "../project/instance"
-import { Identifier } from "../id/id"
 import PROMPT_INITIALIZE from "./template/initialize.txt"
 import PROMPT_REVIEW from "./template/review.txt"
 import { MCP } from "../mcp"
 import { Skill } from "../skill"
+import { Log } from "../util/log"
 
 export namespace Command {
+  const log = Log.create({ service: "command" })
   export const Event = {
     Executed: BusEvent.define(
       "command.executed",
@@ -57,95 +60,126 @@ export namespace Command {
     REVIEW: "review",
   } as const
 
-  const state = Instance.state(async () => {
-    const cfg = await Config.get()
-
-    const result: Record<string, Info> = {
-      [Default.INIT]: {
-        name: Default.INIT,
-        description: "create/update AGENTS.md",
-        source: "command",
-        get template() {
-          return PROMPT_INITIALIZE.replace("${path}", Instance.worktree)
-        },
-        hints: hints(PROMPT_INITIALIZE),
-      },
-      [Default.REVIEW]: {
-        name: Default.REVIEW,
-        description: "review changes [commit|branch|pr], defaults to uncommitted",
-        source: "command",
-        get template() {
-          return PROMPT_REVIEW.replace("${path}", Instance.worktree)
-        },
-        subtask: true,
-        hints: hints(PROMPT_REVIEW),
-      },
-    }
+  export interface Interface {
+    readonly get: (name: string) => Effect.Effect<Info | undefined>
+    readonly list: () => Effect.Effect<Info[]>
+  }
 
-    for (const [name, command] of Object.entries(cfg.command ?? {})) {
-      result[name] = {
-        name,
-        agent: command.agent,
-        model: command.model,
-        description: command.description,
-        source: "command",
-        get template() {
-          return command.template
-        },
-        subtask: command.subtask,
-        hints: hints(command.template),
-      }
-    }
-    for (const [name, prompt] of Object.entries(await MCP.prompts())) {
-      result[name] = {
-        name,
-        source: "mcp",
-        description: prompt.description,
-        get template() {
-          // since a getter can't be async we need to manually return a promise here
-          return new Promise<string>(async (resolve, reject) => {
-            const template = await MCP.getPrompt(
-              prompt.client,
-              prompt.name,
-              prompt.arguments
-                ? // substitute each argument with $1, $2, etc.
-                  Object.fromEntries(prompt.arguments?.map((argument, i) => [argument.name, `$${i + 1}`]))
-                : {},
-            ).catch(reject)
-            resolve(
-              template?.messages
-                .map((message) => (message.content.type === "text" ? message.content.text : ""))
-                .join("\n") || "",
-            )
-          })
-        },
-        hints: prompt.arguments?.map((_, i) => `$${i + 1}`) ?? [],
-      }
-    }
+  export class Service extends ServiceMap.Service<Service, Interface>()("@opencode/Command") {}
 
-    // Add skills as invokable commands
-    for (const skill of await Skill.all()) {
-      // Skip if a command with this name already exists
-      if (result[skill.name]) continue
-      result[skill.name] = {
-        name: skill.name,
-        description: skill.description,
-        source: "skill",
-        get template() {
-          return skill.content
-        },
-        hints: [],
-      }
-    }
+  export const layer = Layer.effect(
+    Service,
+    Effect.gen(function* () {
+      const instance = yield* InstanceContext
 
-    return result
-  })
+      const commands: Record<string, Info> = {}
+
+      const load = Effect.fn("Command.load")(function* () {
+        yield* Effect.promise(async () => {
+          const cfg = await Config.get()
+
+          commands[Default.INIT] = {
+            name: Default.INIT,
+            description: "create/update AGENTS.md",
+            source: "command",
+            get template() {
+              return PROMPT_INITIALIZE.replace("${path}", instance.worktree)
+            },
+            hints: hints(PROMPT_INITIALIZE),
+          }
+          commands[Default.REVIEW] = {
+            name: Default.REVIEW,
+            description: "review changes [commit|branch|pr], defaults to uncommitted",
+            source: "command",
+            get template() {
+              return PROMPT_REVIEW.replace("${path}", instance.worktree)
+            },
+            subtask: true,
+            hints: hints(PROMPT_REVIEW),
+          }
+
+          for (const [name, command] of Object.entries(cfg.command ?? {})) {
+            commands[name] = {
+              name,
+              agent: command.agent,
+              model: command.model,
+              description: command.description,
+              source: "command",
+              get template() {
+                return command.template
+              },
+              subtask: command.subtask,
+              hints: hints(command.template),
+            }
+          }
+          for (const [name, prompt] of Object.entries(await MCP.prompts())) {
+            commands[name] = {
+              name,
+              source: "mcp",
+              description: prompt.description,
+              get template() {
+                // since a getter can't be async we need to manually return a promise here
+                return new Promise<string>(async (resolve, reject) => {
+                  const template = await MCP.getPrompt(
+                    prompt.client,
+                    prompt.name,
+                    prompt.arguments
+                      ? // substitute each argument with $1, $2, etc.
+                        Object.fromEntries(prompt.arguments?.map((argument, i) => [argument.name, `$${i + 1}`]))
+                      : {},
+                  ).catch(reject)
+                  resolve(
+                    template?.messages
+                      .map((message) => (message.content.type === "text" ? message.content.text : ""))
+                      .join("\n") || "",
+                  )
+                })
+              },
+              hints: prompt.arguments?.map((_, i) => `$${i + 1}`) ?? [],
+            }
+          }
+
+          // Add skills as invokable commands
+          for (const skill of await Skill.all()) {
+            // Skip if a command with this name already exists
+            if (commands[skill.name]) continue
+            commands[skill.name] = {
+              name: skill.name,
+              description: skill.description,
+              source: "skill",
+              get template() {
+                return skill.content
+              },
+              hints: [],
+            }
+          }
+        })
+      })
+
+      const loadFiber = yield* load().pipe(
+        Effect.catchCause((cause) => Effect.sync(() => log.error("init failed", { cause }))),
+        Effect.forkScoped,
+      )
+
+      const get = Effect.fn("Command.get")(function* (name: string) {
+        yield* Fiber.join(loadFiber)
+        return commands[name]
+      })
+
+      const list = Effect.fn("Command.list")(function* () {
+        yield* Fiber.join(loadFiber)
+        return Object.values(commands)
+      })
+
+      return Service.of({ get, list })
+    }),
+  )
 
   export async function get(name: string) {
-    return state().then((x) => x[name])
+    return runPromiseInstance(Service.use((svc) => svc.get(name)))
   }
 
   export async function list() {
-    return state().then((x) => Object.values(x))
+    return runPromiseInstance(Service.use((svc) => svc.list()))
   }
 }
diff --git a/packages/opencode/src/control-plane/workspace.ts b/packages/opencode/src/control-plane/workspace.ts
index e5294844b148..b519895b2fc5 100644
--- a/packages/opencode/src/control-plane/workspace.ts
+++ b/packages/opencode/src/control-plane/workspace.ts
@@ -124,7 +124,7 @@ export namespace Workspace {
       await parseSSE(res.body, stop, (event) => {
         GlobalBus.emit("event", {
           directory: space.id,
-          payload: event,
+          payload: event as { type: string; properties: Record<string, unknown> },
         })
       })
       // Wait 250ms and retry if SSE connection fails
diff --git a/packages/opencode/src/effect/instances.ts b/packages/opencode/src/effect/instances.ts
index 6fcfddb24f58..63908632b89a 100644
--- a/packages/opencode/src/effect/instances.ts
+++ b/packages/opencode/src/effect/instances.ts
@@ -1,4 +1,5 @@
 import { Effect, Layer, LayerMap, ServiceMap } from "effect"
+import { Command } from "@/command"
 import { File } from "@/file/service"
 import { FileTime } from "@/file/time-service"
 import { FileWatcher } from "@/file/watcher"
@@ -16,6 +17,7 @@ import { registerDisposer } from "./instance-registry"
 export { InstanceContext } from "./instance-context"
 
 export type InstanceServices =
+  | Command.Service
   | Question.Service
   | Permission.Service
   | ProviderAuth.Service
@@ -36,6 +38,7 @@ export type InstanceServices =
 function lookup(_key: string) {
   const ctx = Layer.sync(InstanceContext, () => InstanceContext.of(Instance.current))
   return Layer.mergeAll(
+    Command.layer,
     Question.layer,
     Permission.layer,
     ProviderAuth.defaultLayer,
diff --git a/packages/opencode/src/session/prompt.ts b/packages/opencode/src/session/prompt.ts
index bac958ec1033..fdeacc1d12f7 100644
--- a/packages/opencode/src/session/prompt.ts
+++ b/packages/opencode/src/session/prompt.ts
@@ -1782,6 +1782,9 @@ NOTE: At any point in time through this workflow you should feel free to ask the
   export async function command(input: CommandInput) {
     log.info("command", input)
     const command = await Command.get(input.command)
+    if (!command) {
+      throw new NamedError.Unknown({ message: `Command not found: "${input.command}"` })
+    }
     const agentName = command.agent ?? input.agent ?? (await Agent.defaultAgent())
 
     const raw = input.arguments.match(argsRegex) ?? []
diff --git a/packages/opencode/test/file/watcher.test.ts b/packages/opencode/test/file/watcher.test.ts
index 2cd27643e88c..d4893e963e97 100644
--- a/packages/opencode/test/file/watcher.test.ts
+++ b/packages/opencode/test/file/watcher.test.ts
@@ -16,7 +16,7 @@ const describeWatcher = FileWatcher.hasNativeBinding() && !process.env.CI ? desc
 // Helpers
 // ---------------------------------------------------------------------------
 
-type BusUpdate = { directory?: string; payload: { type: string; properties: WatcherEvent } }
+type BusUpdate = { directory?: string; payload: { type: string; properties: Record<string, unknown> } }
 type WatcherEvent = { file: string; event: "add" | "change" | "unlink" }
 
 /** Run `body` with a live FileWatcher service. */
@@ -40,18 +40,18 @@ function listen(directory: string, check: (evt: WatcherEvent) => boolean, hit: (
     if (done) return
     if (evt.directory !== directory) return
     if (evt.payload.type !== FileWatcher.Event.Updated.type) return
-    if (!check(evt.payload.properties)) return
-    hit(evt.payload.properties)
+    const props = evt.payload.properties as WatcherEvent
+    if (!check(props)) return
+    hit(props)
   }
 
-  function cleanup() {
+  GlobalBus.on("event", on)
+
+  return () => {
     if (done) return
     done = true
     GlobalBus.off("event", on)
   }
-
-  GlobalBus.on("event", on)
-  return cleanup
 }
 
 function wait(directory: string, check: (evt: WatcherEvent) => boolean) {