diff --git a/packages/opencode/src/bus/bus-event.ts b/packages/opencode/src/bus/bus-event.ts
index efaed94406..f27d263354 100644
--- a/packages/opencode/src/bus/bus-event.ts
+++ b/packages/opencode/src/bus/bus-event.ts
@@ -1,15 +1,19 @@
 import z from "zod"
-import type { ZodType } from "zod"
+import { Schema } from "effect"
+import { zodObject } from "@/util/effect-zod"
 
-export type Definition = ReturnType<typeof define>
+export type Definition<Type extends string = string, Properties extends Schema.Top = Schema.Top> = {
+  type: Type
+  properties: Properties
+}
 
 const registry = new Map<string, Definition>()
 
-export function define<Type extends string, Properties extends ZodType>(type: Type, properties: Properties) {
-  const result = {
-    type,
-    properties,
-  }
+export function define<Type extends string, Properties extends Schema.Top>(
+  type: Type,
+  properties: Properties,
+): Definition<Type, Properties> {
+  const result = { type, properties }
   registry.set(type, result)
   return result
 }
@@ -21,7 +25,7 @@ export function payloads() {
       return z
         .object({
           type: z.literal(type),
-          properties: def.properties,
+          properties: zodObject(def.properties),
         })
         .meta({
           ref: `Event.${def.type}`,
diff --git a/packages/opencode/src/bus/index.ts b/packages/opencode/src/bus/index.ts
index 9183ff72a4..12251f26c7 100644
--- a/packages/opencode/src/bus/index.ts
+++ b/packages/opencode/src/bus/index.ts
@@ -1,5 +1,4 @@
-import z from "zod"
-import { Effect, Exit, Layer, PubSub, Scope, Context, Stream, Schema as EffectSchema, Types } from "effect"
+import { Effect, Exit, Layer, PubSub, Scope, Context, Stream, Schema } from "effect"
 import { EffectBridge } from "@/effect"
 import { Log } from "../util"
 import { BusEvent } from "./bus-event"
@@ -9,16 +8,12 @@ import { makeRuntime } from "@/effect/run-service"
 
 const log = Log.create({ service: "bus" })
 
-type BusProperties<D extends BusEvent.Definition = BusEvent.Definition> = D extends {
-  effectProperties: infer Properties extends EffectSchema.Top
-}
-  ? Types.DeepMutable<EffectSchema.Schema.Type<Properties>>
-  : z.infer<D["properties"]>
+type BusProperties<D extends BusEvent.Definition<string, Schema.Top>> = Schema.Schema.Type<D["properties"]>
 
 export const InstanceDisposed = BusEvent.define(
   "server.instance.disposed",
-  z.object({
-    directory: z.string(),
+  Schema.Struct({
+    directory: Schema.String,
   }),
 )
 
diff --git a/packages/opencode/src/cli/cmd/tui/event.ts b/packages/opencode/src/cli/cmd/tui/event.ts
index fa164d53e8..ab85b1e645 100644
--- a/packages/opencode/src/cli/cmd/tui/event.ts
+++ b/packages/opencode/src/cli/cmd/tui/event.ts
@@ -1,14 +1,14 @@
 import { BusEvent } from "@/bus/bus-event"
 import { SessionID } from "@/session/schema"
-import z from "zod"
+import { Schema } from "effect"
 
 export const TuiEvent = {
-  PromptAppend: BusEvent.define("tui.prompt.append", z.object({ text: z.string() })),
+  PromptAppend: BusEvent.define("tui.prompt.append", Schema.Struct({ text: Schema.String })),
   CommandExecute: BusEvent.define(
     "tui.command.execute",
-    z.object({
-      command: z.union([
-        z.enum([
+    Schema.Struct({
+      command: Schema.Union([
+        Schema.Literals([
           "session.list",
           "session.new",
           "session.share",
@@ -26,23 +26,23 @@ export const TuiEvent = {
           "prompt.submit",
           "agent.cycle",
         ]),
-        z.string(),
+        Schema.String,
       ]),
     }),
   ),
   ToastShow: BusEvent.define(
     "tui.toast.show",
-    z.object({
-      title: z.string().optional(),
-      message: z.string(),
-      variant: z.enum(["info", "success", "warning", "error"]),
-      duration: z.number().default(5000).optional().describe("Duration in milliseconds"),
+    Schema.Struct({
+      title: Schema.optional(Schema.String),
+      message: Schema.String,
+      variant: Schema.Literals(["info", "success", "warning", "error"]),
+      duration: Schema.optional(Schema.Number).annotate({ description: "Duration in milliseconds" }),
     }),
   ),
   SessionSelect: BusEvent.define(
     "tui.session.select",
-    z.object({
-      sessionID: SessionID.zod.describe("Session ID to navigate to"),
+    Schema.Struct({
+      sessionID: SessionID.annotate({ description: "Session ID to navigate to" }),
     }),
   ),
 }
diff --git a/packages/opencode/src/cli/cmd/tui/ui/toast.tsx b/packages/opencode/src/cli/cmd/tui/ui/toast.tsx
index f534d90b77..69674ba7ce 100644
--- a/packages/opencode/src/cli/cmd/tui/ui/toast.tsx
+++ b/packages/opencode/src/cli/cmd/tui/ui/toast.tsx
@@ -4,10 +4,10 @@ import { useTheme } from "@tui/context/theme"
 import { useTerminalDimensions } from "@opentui/solid"
 import { SplitBorder } from "../component/border"
 import { TextAttributes } from "@opentui/core"
-import z from "zod"
+import { Schema } from "effect"
 import { type TuiEvent } from "../event"
 
-export type ToastOptions = z.infer<typeof TuiEvent.ToastShow.properties>
+export type ToastOptions = Schema.Schema.Type<typeof TuiEvent.ToastShow.properties>
 
 export function Toast() {
   const toast = useToast()
diff --git a/packages/opencode/src/command/index.ts b/packages/opencode/src/command/index.ts
index 27ba357ecc..478a12f664 100644
--- a/packages/opencode/src/command/index.ts
+++ b/packages/opencode/src/command/index.ts
@@ -3,7 +3,7 @@ import { InstanceState } from "@/effect"
 import { EffectBridge } from "@/effect"
 import type { InstanceContext } from "@/project/instance"
 import { SessionID, MessageID } from "@/session/schema"
-import { Effect, Layer, Context } from "effect"
+import { Effect, Layer, Context, Schema } from "effect"
 import z from "zod"
 import { Config } from "../config"
 import { MCP } from "../mcp"
@@ -18,11 +18,11 @@ type State = {
 export const Event = {
   Executed: BusEvent.define(
     "command.executed",
-    z.object({
-      name: z.string(),
-      sessionID: SessionID.zod,
-      arguments: z.string(),
-      messageID: MessageID.zod,
+    Schema.Struct({
+      name: Schema.String,
+      sessionID: SessionID,
+      arguments: Schema.String,
+      messageID: MessageID,
     }),
   ),
 }
diff --git a/packages/opencode/src/config/config.ts b/packages/opencode/src/config/config.ts
index 9814017d10..eab199232a 100644
--- a/packages/opencode/src/config/config.ts
+++ b/packages/opencode/src/config/config.ts
@@ -25,7 +25,7 @@ import { Context, Duration, Effect, Exit, Fiber, Layer, Option, Schema } from "e
 import { EffectFlock } from "@opencode-ai/shared/util/effect-flock"
 import { InstanceRef } from "@/effect/instance-ref"
 import { zod, ZodOverride } from "@/util/effect-zod"
-import { NonNegativeInt, PositiveInt, withStatics } from "@/util/schema"
+import { NonNegativeInt, PositiveInt, withStatics, type DeepMutable } from "@/util/schema"
 import { ConfigAgent } from "./agent"
 import { ConfigCommand } from "./command"
 import { ConfigFormatter } from "./formatter"
@@ -249,26 +249,9 @@ export const Info = Schema.Struct({
     })),
   )
 
-// Schema.Struct produces readonly types by default, but the service code
-// below mutates Info objects directly (e.g. `config.mode = ...`). Strip the
-// readonly recursively so callers get the same mutable shape zod inferred.
-//
-// `Types.DeepMutable` from effect-smol would be a drop-in, but its fallback
-// branch `{ -readonly [K in keyof T]: ... }` collapses `unknown` to `{}`
-// (since `keyof unknown = never`), which widens `Record<string, unknown>`
-// fields like `ConfigPlugin.Options`. The local version gates on
-// `extends object` so `unknown` passes through.
-//
-// Tuple branch preserves `ConfigPlugin.Spec`'s `readonly [string, Options]`
-// shape (otherwise the general array branch widens it to an array).
-type DeepMutable<T> = T extends readonly [unknown, ...unknown[]]
-  ? { -readonly [K in keyof T]: DeepMutable<T[K]> }
-  : T extends readonly (infer U)[]
-    ? DeepMutable<U>[]
-    : T extends object
-      ? { -readonly [K in keyof T]: DeepMutable<T[K]> }
-      : T
-
+// Uses the shared `DeepMutable` from `@/util/schema`. See the definition
+// there for why the local variant is needed over `Types.DeepMutable` from
+// effect-smol (the upstream version collapses `unknown` to `{}`).
 export type Info = DeepMutable<Schema.Schema.Type<typeof Info>> & {
   // plugin_origins is derived state, not a persisted config field. It keeps each winning plugin spec together
   // with the file and scope it came from so later runtime code can make location-sensitive decisions.
diff --git a/packages/opencode/src/control-plane/workspace.ts b/packages/opencode/src/control-plane/workspace.ts
index eb689df025..8519cb06c1 100644
--- a/packages/opencode/src/control-plane/workspace.ts
+++ b/packages/opencode/src/control-plane/workspace.ts
@@ -1,4 +1,5 @@
 import z from "zod"
+import { Schema } from "effect"
 import { setTimeout as sleep } from "node:timers/promises"
 import { fn } from "@/util/fn"
 import { Database, asc, eq, inArray } from "@/storage"
@@ -25,36 +26,37 @@ import { errorData } from "@/util/error"
 import { AppRuntime } from "@/effect/app-runtime"
 import { waitEvent } from "./util"
 import { WorkspaceContext } from "./workspace-context"
+import { NonNegativeInt } from "@/util/schema"
 
 export const Info = WorkspaceInfo.meta({
   ref: "Workspace",
 })
 export type Info = z.infer<typeof Info>
 
-export const ConnectionStatus = z.object({
-  workspaceID: WorkspaceID.zod,
-  status: z.enum(["connected", "connecting", "disconnected", "error"]),
+export const ConnectionStatus = Schema.Struct({
+  workspaceID: WorkspaceID,
+  status: Schema.Literals(["connected", "connecting", "disconnected", "error"]),
 })
-export type ConnectionStatus = z.infer<typeof ConnectionStatus>
+export type ConnectionStatus = Schema.Schema.Type<typeof ConnectionStatus>
 
-const Restore = z.object({
-  workspaceID: WorkspaceID.zod,
-  sessionID: SessionID.zod,
-  total: z.number().int().min(0),
-  step: z.number().int().min(0),
+const Restore = Schema.Struct({
+  workspaceID: WorkspaceID,
+  sessionID: SessionID,
+  total: NonNegativeInt,
+  step: NonNegativeInt,
 })
 
 export const Event = {
   Ready: BusEvent.define(
     "workspace.ready",
-    z.object({
-      name: z.string(),
+    Schema.Struct({
+      name: Schema.String,
     }),
   ),
   Failed: BusEvent.define(
     "workspace.failed",
-    z.object({
-      message: z.string(),
+    Schema.Struct({
+      message: Schema.String,
     }),
   ),
   Restore: BusEvent.define("workspace.restore", Restore),
diff --git a/packages/opencode/src/file/index.ts b/packages/opencode/src/file/index.ts
index af4fbf76c8..ca791e4128 100644
--- a/packages/opencode/src/file/index.ts
+++ b/packages/opencode/src/file/index.ts
@@ -3,7 +3,7 @@ import { InstanceState } from "@/effect"
 
 import { AppFileSystem } from "@opencode-ai/shared/filesystem"
 import { Git } from "@/git"
-import { Effect, Layer, Context, Scope } from "effect"
+import { Effect, Layer, Context, Schema, Scope } from "effect"
 import * as Stream from "effect/Stream"
 import { formatPatch, structuredPatch } from "diff"
 import fuzzysort from "fuzzysort"
@@ -76,8 +76,8 @@ export type Content = z.infer<typeof Content>
 export const Event = {
   Edited: BusEvent.define(
     "file.edited",
-    z.object({
-      file: z.string(),
+    Schema.Struct({
+      file: Schema.String,
     }),
   ),
 }
diff --git a/packages/opencode/src/file/watcher.ts b/packages/opencode/src/file/watcher.ts
index dc20333758..0ac98b9c2d 100644
--- a/packages/opencode/src/file/watcher.ts
+++ b/packages/opencode/src/file/watcher.ts
@@ -1,4 +1,4 @@
-import { Cause, Effect, Layer, Context } from "effect"
+import { Cause, Effect, Layer, Context, Schema } from "effect"
 // @ts-ignore
 import { createWrapper } from "@parcel/watcher/wrapper"
 import type ParcelWatcher from "@parcel/watcher"
@@ -25,9 +25,9 @@ const SUBSCRIBE_TIMEOUT_MS = 10_000
 export const Event = {
   Updated: BusEvent.define(
     "file.watcher.updated",
-    z.object({
-      file: z.string(),
-      event: z.union([z.literal("add"), z.literal("change"), z.literal("unlink")]),
+    Schema.Struct({
+      file: Schema.String,
+      event: Schema.Literals(["add", "change", "unlink"]),
     }),
   ),
 }
diff --git a/packages/opencode/src/ide/index.ts b/packages/opencode/src/ide/index.ts
index ee80c34741..f9ce1ec635 100644
--- a/packages/opencode/src/ide/index.ts
+++ b/packages/opencode/src/ide/index.ts
@@ -1,5 +1,6 @@
 import { BusEvent } from "@/bus/bus-event"
 import z from "zod"
+import { Schema } from "effect"
 import { NamedError } from "@opencode-ai/shared/util/error"
 import { Log } from "../util"
 import { Process } from "@/util"
@@ -17,8 +18,8 @@ const log = Log.create({ service: "ide" })
 export const Event = {
   Installed: BusEvent.define(
     "ide.installed",
-    z.object({
-      ide: z.string(),
+    Schema.Struct({
+      ide: Schema.String,
     }),
   ),
 }
diff --git a/packages/opencode/src/installation/index.ts b/packages/opencode/src/installation/index.ts
index 787f9ea8c5..bb3de3f3b5 100644
--- a/packages/opencode/src/installation/index.ts
+++ b/packages/opencode/src/installation/index.ts
@@ -21,14 +21,14 @@ export type ReleaseType = "patch" | "minor" | "major"
 export const Event = {
   Updated: BusEvent.define(
     "installation.updated",
-    z.object({
-      version: z.string(),
+    Schema.Struct({
+      version: Schema.String,
     }),
   ),
   UpdateAvailable: BusEvent.define(
     "installation.update-available",
-    z.object({
-      version: z.string(),
+    Schema.Struct({
+      version: Schema.String,
     }),
   ),
 }
diff --git a/packages/opencode/src/lsp/client.ts b/packages/opencode/src/lsp/client.ts
index f6d5110a6c..e8050babfd 100644
--- a/packages/opencode/src/lsp/client.ts
+++ b/packages/opencode/src/lsp/client.ts
@@ -8,6 +8,7 @@ import { Log } from "../util"
 import { Process } from "../util"
 import { LANGUAGE_EXTENSIONS } from "./language"
 import z from "zod"
+import { Schema } from "effect"
 import type * as LSPServer from "./server"
 import { NamedError } from "@opencode-ai/shared/util/error"
 import { withTimeout } from "../util/timeout"
@@ -41,9 +42,9 @@ export const InitializeError = NamedError.create(
 export const Event = {
   Diagnostics: BusEvent.define(
     "lsp.client.diagnostics",
-    z.object({
-      serverID: z.string(),
-      path: z.string(),
+    Schema.Struct({
+      serverID: Schema.String,
+      path: Schema.String,
     }),
   ),
 }
diff --git a/packages/opencode/src/lsp/lsp.ts b/packages/opencode/src/lsp/lsp.ts
index 4c46cd9aa7..7741ff60e5 100644
--- a/packages/opencode/src/lsp/lsp.ts
+++ b/packages/opencode/src/lsp/lsp.ts
@@ -19,7 +19,7 @@ import { zod, ZodOverride } from "@/util/effect-zod"
 const log = Log.create({ service: "lsp" })
 
 export const Event = {
-  Updated: BusEvent.define("lsp.updated", z.object({})),
+  Updated: BusEvent.define("lsp.updated", Schema.Struct({})),
 }
 
 const Position = Schema.Struct({
diff --git a/packages/opencode/src/mcp/index.ts b/packages/opencode/src/mcp/index.ts
index 09fcfc756a..385d7782a6 100644
--- a/packages/opencode/src/mcp/index.ts
+++ b/packages/opencode/src/mcp/index.ts
@@ -25,7 +25,7 @@ import { BusEvent } from "../bus/bus-event"
 import { Bus } from "@/bus"
 import { TuiEvent } from "@/cli/cmd/tui/event"
 import open from "open"
-import { Effect, Exit, Layer, Option, Context, Stream } from "effect"
+import { Effect, Exit, Layer, Option, Context, Schema, Stream } from "effect"
 import { EffectBridge } from "@/effect"
 import { InstanceState } from "@/effect"
 import { ChildProcess, ChildProcessSpawner } from "effect/unstable/process"
@@ -47,16 +47,16 @@ export type Resource = z.infer<typeof Resource>
 
 export const ToolsChanged = BusEvent.define(
   "mcp.tools.changed",
-  z.object({
-    server: z.string(),
+  Schema.Struct({
+    server: Schema.String,
   }),
 )
 
 export const BrowserOpenFailed = BusEvent.define(
   "mcp.browser.open.failed",
-  z.object({
-    mcpName: z.string(),
-    url: z.string(),
+  Schema.Struct({
+    mcpName: Schema.String,
+    url: Schema.String,
   }),
 )
 
diff --git a/packages/opencode/src/permission/index.ts b/packages/opencode/src/permission/index.ts
index 6943b3d93b..05c832016d 100644
--- a/packages/opencode/src/permission/index.ts
+++ b/packages/opencode/src/permission/index.ts
@@ -73,16 +73,14 @@ export class Approval extends Schema.Class<Approval>("PermissionApproval")({
 }
 
 export const Event = {
-  Asked: BusEvent.define("permission.asked", Request.zod),
+  Asked: BusEvent.define("permission.asked", Request),
   Replied: BusEvent.define(
     "permission.replied",
-    zod(
-      Schema.Struct({
-        sessionID: SessionID,
-        requestID: PermissionID,
-        reply: Reply,
-      }),
-    ),
+    Schema.Struct({
+      sessionID: SessionID,
+      requestID: PermissionID,
+      reply: Reply,
+    }),
   ),
 }
 
diff --git a/packages/opencode/src/project/project.ts b/packages/opencode/src/project/project.ts
index ab60cff7aa..70a9590640 100644
--- a/packages/opencode/src/project/project.ts
+++ b/packages/opencode/src/project/project.ts
@@ -53,7 +53,7 @@ export const Info = Schema.Struct({
 export type Info = Types.DeepMutable<Schema.Schema.Type<typeof Info>>
 
 export const Event = {
-  Updated: BusEvent.define("project.updated", Info.zod),
+  Updated: BusEvent.define("project.updated", Info),
 }
 
 type Row = typeof ProjectTable.$inferSelect
diff --git a/packages/opencode/src/project/vcs.ts b/packages/opencode/src/project/vcs.ts
index ba028f7e8e..e8c6ff2ac7 100644
--- a/packages/opencode/src/project/vcs.ts
+++ b/packages/opencode/src/project/vcs.ts
@@ -1,4 +1,4 @@
-import { Effect, Layer, Context, Stream, Scope } from "effect"
+import { Effect, Layer, Context, Schema, Stream, Scope } from "effect"
 import { formatPatch, structuredPatch } from "diff"
 import path from "path"
 import { Bus } from "@/bus"
@@ -107,8 +107,8 @@ export type Mode = z.infer<typeof Mode>
 export const Event = {
   BranchUpdated: BusEvent.define(
     "vcs.branch.updated",
-    z.object({
-      branch: z.string().optional(),
+    Schema.Struct({
+      branch: Schema.optional(Schema.String),
     }),
   ),
 }
diff --git a/packages/opencode/src/pty/index.ts b/packages/opencode/src/pty/index.ts
index 3d00de596a..604fa77fbb 100644
--- a/packages/opencode/src/pty/index.ts
+++ b/packages/opencode/src/pty/index.ts
@@ -3,13 +3,14 @@ import { Bus } from "@/bus"
 import { InstanceState } from "@/effect"
 import { Instance } from "@/project/instance"
 import type { Proc } from "#pty"
-import z from "zod"
 import { Log } from "../util"
 import { lazy } from "@opencode-ai/shared/util/lazy"
 import { Shell } from "@/shell/shell"
 import { Plugin } from "@/plugin"
 import { PtyID } from "./schema"
-import { Effect, Layer, Context } from "effect"
+import { Effect, Layer, Context, Schema, Types } from "effect"
+import { zod } from "@/util/effect-zod"
+import { withStatics } from "@/util/schema"
 import { EffectBridge } from "@/effect"
 
 const log = Log.create({ service: "pty" })
@@ -53,47 +54,47 @@ const meta = (cursor: number) => {
 
 const pty = lazy(() => import("#pty"))
 
-export const Info = z
-  .object({
-    id: PtyID.zod,
-    title: z.string(),
-    command: z.string(),
-    args: z.array(z.string()),
-    cwd: z.string(),
-    status: z.enum(["running", "exited"]),
-    pid: z.number(),
-  })
-  .meta({ ref: "Pty" })
-
-export type Info = z.infer<typeof Info>
-
-export const CreateInput = z.object({
-  command: z.string().optional(),
-  args: z.array(z.string()).optional(),
-  cwd: z.string().optional(),
-  title: z.string().optional(),
-  env: z.record(z.string(), z.string()).optional(),
+export const Info = Schema.Struct({
+  id: PtyID,
+  title: Schema.String,
+  command: Schema.String,
+  args: Schema.Array(Schema.String),
+  cwd: Schema.String,
+  status: Schema.Literals(["running", "exited"]),
+  pid: Schema.Number,
 })
+  .annotate({ identifier: "Pty" })
+  .pipe(withStatics((s) => ({ zod: zod(s) })))
 
-export type CreateInput = z.infer<typeof CreateInput>
+export type Info = Types.DeepMutable<Schema.Schema.Type<typeof Info>>
 
-export const UpdateInput = z.object({
-  title: z.string().optional(),
-  size: z
-    .object({
-      rows: z.number(),
-      cols: z.number(),
-    })
-    .optional(),
-})
+export const CreateInput = Schema.Struct({
+  command: Schema.optional(Schema.String),
+  args: Schema.optional(Schema.Array(Schema.String)),
+  cwd: Schema.optional(Schema.String),
+  title: Schema.optional(Schema.String),
+  env: Schema.optional(Schema.Record(Schema.String, Schema.String)),
+}).pipe(withStatics((s) => ({ zod: zod(s) })))
 
-export type UpdateInput = z.infer<typeof UpdateInput>
+export type CreateInput = Types.DeepMutable<Schema.Schema.Type<typeof CreateInput>>
+
+export const UpdateInput = Schema.Struct({
+  title: Schema.optional(Schema.String),
+  size: Schema.optional(
+    Schema.Struct({
+      rows: Schema.Number,
+      cols: Schema.Number,
+    }),
+  ),
+}).pipe(withStatics((s) => ({ zod: zod(s) })))
+
+export type UpdateInput = Types.DeepMutable<Schema.Schema.Type<typeof UpdateInput>>
 
 export const Event = {
-  Created: BusEvent.define("pty.created", z.object({ info: Info })),
-  Updated: BusEvent.define("pty.updated", z.object({ info: Info })),
-  Exited: BusEvent.define("pty.exited", z.object({ id: PtyID.zod, exitCode: z.number() })),
-  Deleted: BusEvent.define("pty.deleted", z.object({ id: PtyID.zod })),
+  Created: BusEvent.define("pty.created", Schema.Struct({ info: Info })),
+  Updated: BusEvent.define("pty.updated", Schema.Struct({ info: Info })),
+  Exited: BusEvent.define("pty.exited", Schema.Struct({ id: PtyID, exitCode: Schema.Number })),
+  Deleted: BusEvent.define("pty.deleted", Schema.Struct({ id: PtyID })),
 }
 
 export interface Interface {
diff --git a/packages/opencode/src/question/index.ts b/packages/opencode/src/question/index.ts
index 3b377c9827..626c71826c 100644
--- a/packages/opencode/src/question/index.ts
+++ b/packages/opencode/src/question/index.ts
@@ -94,9 +94,9 @@ class Rejected extends Schema.Class<Rejected>("QuestionRejected")({
 }) {}
 
 export const Event = {
-  Asked: BusEvent.define("question.asked", Request.zod),
-  Replied: BusEvent.define("question.replied", zod(Replied)),
-  Rejected: BusEvent.define("question.rejected", zod(Rejected)),
+  Asked: BusEvent.define("question.asked", Request),
+  Replied: BusEvent.define("question.replied", Replied),
+  Rejected: BusEvent.define("question.rejected", Rejected),
 }
 
 export class RejectedError extends Schema.TaggedErrorClass<RejectedError>()("QuestionRejectedError", {}) {
@@ -194,7 +194,7 @@ export const layer = Layer.effect(
       yield* bus.publish(Event.Replied, {
         sessionID: existing.info.sessionID,
         requestID: existing.info.id,
-        answers: input.answers,
+        answers: input.answers.map((a) => [...a]),
       })
       yield* Deferred.succeed(existing.deferred, input.answers)
     })
diff --git a/packages/opencode/src/server/event.ts b/packages/opencode/src/server/event.ts
index 49325b2bb6..d5f10f47db 100644
--- a/packages/opencode/src/server/event.ts
+++ b/packages/opencode/src/server/event.ts
@@ -1,7 +1,7 @@
 import { BusEvent } from "@/bus/bus-event"
-import z from "zod"
+import { Schema } from "effect"
 
 export const Event = {
-  Connected: BusEvent.define("server.connected", z.object({})),
-  Disposed: BusEvent.define("global.disposed", z.object({})),
+  Connected: BusEvent.define("server.connected", Schema.Struct({})),
+  Disposed: BusEvent.define("global.disposed", Schema.Struct({})),
 }
diff --git a/packages/opencode/src/server/routes/control/workspace.ts b/packages/opencode/src/server/routes/control/workspace.ts
index 9ff747b68a..d48c687f31 100644
--- a/packages/opencode/src/server/routes/control/workspace.ts
+++ b/packages/opencode/src/server/routes/control/workspace.ts
@@ -3,6 +3,7 @@ import { describeRoute, resolver, validator } from "hono-openapi"
 import z from "zod"
 import { listAdaptors } from "@/control-plane/adaptors"
 import { Workspace } from "@/control-plane/workspace"
+import { zodObject } from "@/util/effect-zod"
 import { Instance } from "@/project/instance"
 import { errors } from "../../error"
 import { lazy } from "@/util/lazy"
@@ -107,7 +108,7 @@ export const WorkspaceRoutes = lazy(() =>
             description: "Workspace status",
             content: {
               "application/json": {
-                schema: resolver(z.array(Workspace.ConnectionStatus)),
+                schema: resolver(z.array(zodObject(Workspace.ConnectionStatus))),
               },
             },
           },
diff --git a/packages/opencode/src/server/routes/global.ts b/packages/opencode/src/server/routes/global.ts
index 54f9972e02..a1199a4691 100644
--- a/packages/opencode/src/server/routes/global.ts
+++ b/packages/opencode/src/server/routes/global.ts
@@ -1,7 +1,7 @@
 import { Hono, type Context } from "hono"
 import { describeRoute, resolver, validator } from "hono-openapi"
 import { streamSSE } from "hono/streaming"
-import { Effect } from "effect"
+import { Effect, Schema } from "effect"
 import z from "zod"
 import { BusEvent } from "@/bus/bus-event"
 import { SyncEvent } from "@/sync"
@@ -18,7 +18,7 @@ import { errors } from "../error"
 
 const log = Log.create({ service: "server" })
 
-export const GlobalDisposedEvent = BusEvent.define("global.disposed", z.object({}))
+export const GlobalDisposedEvent = BusEvent.define("global.disposed", Schema.Struct({}))
 
 async function streamEvents(c: Context, subscribe: (q: AsyncQueue<string | null>) => () => void) {
   return streamSSE(c, async (stream) => {
diff --git a/packages/opencode/src/server/routes/instance/pty.ts b/packages/opencode/src/server/routes/instance/pty.ts
index a25b66e9ff..51c4699241 100644
--- a/packages/opencode/src/server/routes/instance/pty.ts
+++ b/packages/opencode/src/server/routes/instance/pty.ts
@@ -23,7 +23,7 @@ export function PtyRoutes(upgradeWebSocket: UpgradeWebSocket) {
             description: "List of sessions",
             content: {
               "application/json": {
-                schema: resolver(Pty.Info.array()),
+                schema: resolver(Pty.Info.zod.array()),
               },
             },
           },
@@ -46,18 +46,18 @@ export function PtyRoutes(upgradeWebSocket: UpgradeWebSocket) {
             description: "Created session",
             content: {
               "application/json": {
-                schema: resolver(Pty.Info),
+                schema: resolver(Pty.Info.zod),
               },
             },
           },
           ...errors(400),
         },
       }),
-      validator("json", Pty.CreateInput),
+      validator("json", Pty.CreateInput.zod),
       async (c) =>
         jsonRequest("PtyRoutes.create", c, function* () {
           const pty = yield* Pty.Service
-          return yield* pty.create(c.req.valid("json"))
+          return yield* pty.create(c.req.valid("json") as Pty.CreateInput)
         }),
     )
     .get(
@@ -71,7 +71,7 @@ export function PtyRoutes(upgradeWebSocket: UpgradeWebSocket) {
             description: "Session info",
             content: {
               "application/json": {
-                schema: resolver(Pty.Info),
+                schema: resolver(Pty.Info.zod),
               },
             },
           },
@@ -105,7 +105,7 @@ export function PtyRoutes(upgradeWebSocket: UpgradeWebSocket) {
             description: "Updated session",
             content: {
               "application/json": {
-                schema: resolver(Pty.Info),
+                schema: resolver(Pty.Info.zod),
               },
             },
           },
@@ -113,11 +113,11 @@ export function PtyRoutes(upgradeWebSocket: UpgradeWebSocket) {
         },
       }),
       validator("param", z.object({ ptyID: PtyID.zod })),
-      validator("json", Pty.UpdateInput),
+      validator("json", Pty.UpdateInput.zod),
       async (c) =>
         jsonRequest("PtyRoutes.update", c, function* () {
           const pty = yield* Pty.Service
-          return yield* pty.update(c.req.valid("param").ptyID, c.req.valid("json"))
+          return yield* pty.update(c.req.valid("param").ptyID, c.req.valid("json") as Pty.UpdateInput)
         }),
     )
     .delete(
diff --git a/packages/opencode/src/server/routes/instance/tui.ts b/packages/opencode/src/server/routes/instance/tui.ts
index d6add67b97..a610590e87 100644
--- a/packages/opencode/src/server/routes/instance/tui.ts
+++ b/packages/opencode/src/server/routes/instance/tui.ts
@@ -1,9 +1,12 @@
 import { Hono, type Context } from "hono"
 import { describeRoute, validator, resolver } from "hono-openapi"
+import { Schema } from "effect"
 import z from "zod"
 import { Bus } from "@/bus"
 import { Session } from "@/session"
+import type { SessionID } from "@/session/schema"
 import { TuiEvent } from "@/cli/cmd/tui/event"
+import { zodObject } from "@/util/effect-zod"
 import { AsyncQueue } from "@/util/queue"
 import { errors } from "../../error"
 import { lazy } from "@/util/lazy"
@@ -96,9 +99,9 @@ export const TuiRoutes = lazy(() =>
           ...errors(400),
         },
       }),
-      validator("json", TuiEvent.PromptAppend.properties),
+      validator("json", zodObject(TuiEvent.PromptAppend.properties)),
       async (c) => {
-        await Bus.publish(TuiEvent.PromptAppend, c.req.valid("json"))
+        await Bus.publish(TuiEvent.PromptAppend, c.req.valid("json") as { text: string })
         return c.json(true)
       },
     )
@@ -305,9 +308,9 @@ export const TuiRoutes = lazy(() =>
           },
         },
       }),
-      validator("json", TuiEvent.ToastShow.properties),
+      validator("json", zodObject(TuiEvent.ToastShow.properties)),
       async (c) => {
-        await Bus.publish(TuiEvent.ToastShow, c.req.valid("json"))
+        await Bus.publish(TuiEvent.ToastShow, c.req.valid("json") as Schema.Schema.Type<typeof TuiEvent.ToastShow.properties>)
         return c.json(true)
       },
     )
@@ -336,7 +339,7 @@ export const TuiRoutes = lazy(() =>
             return z
               .object({
                 type: z.literal(def.type),
-                properties: def.properties,
+                properties: zodObject(def.properties),
               })
               .meta({
                 ref: `Event.${def.type}`,
@@ -345,8 +348,9 @@ export const TuiRoutes = lazy(() =>
         ),
       ),
       async (c) => {
-        const evt = c.req.valid("json")
-        await Bus.publish(Object.values(TuiEvent).find((def) => def.type === evt.type)!, evt.properties)
+        const evt = c.req.valid("json") as { type: string; properties: Record<string, unknown> }
+        // eslint-disable-next-line @typescript-eslint/no-explicit-any
+        await Bus.publish(Object.values(TuiEvent).find((def) => def.type === evt.type)! as any, evt.properties as any)
         return c.json(true)
       },
     )
@@ -368,9 +372,9 @@ export const TuiRoutes = lazy(() =>
           ...errors(400, 404),
         },
       }),
-      validator("json", TuiEvent.SessionSelect.properties),
+      validator("json", zodObject(TuiEvent.SessionSelect.properties)),
       async (c) => {
-        const { sessionID } = c.req.valid("json")
+        const { sessionID } = c.req.valid("json") as { sessionID: SessionID }
         await runRequest(
           "TuiRoutes.sessionSelect",
           c,
diff --git a/packages/opencode/src/session/compaction.ts b/packages/opencode/src/session/compaction.ts
index defdb870d7..dc126e6837 100644
--- a/packages/opencode/src/session/compaction.ts
+++ b/packages/opencode/src/session/compaction.ts
@@ -13,7 +13,7 @@ import { Plugin } from "@/plugin"
 import { Config } from "@/config"
 import { NotFoundError } from "@/storage"
 import { ModelID, ProviderID } from "@/provider/schema"
-import { Effect, Layer, Context } from "effect"
+import { Effect, Layer, Context, Schema } from "effect"
 import { InstanceState } from "@/effect"
 import { isOverflow as overflow, usable } from "./overflow"
 import { makeRuntime } from "@/effect/run-service"
@@ -24,8 +24,8 @@ const log = Log.create({ service: "session.compaction" })
 export const Event = {
   Compacted: BusEvent.define(
     "session.compacted",
-    z.object({
-      sessionID: SessionID.zod,
+    Schema.Struct({
+      sessionID: SessionID,
     }),
   ),
 }
diff --git a/packages/opencode/src/session/message-v2.ts b/packages/opencode/src/session/message-v2.ts
index c5a35c7b41..d04645b736 100644
--- a/packages/opencode/src/session/message-v2.ts
+++ b/packages/opencode/src/session/message-v2.ts
@@ -617,12 +617,12 @@ export const Event = {
   }),
   PartDelta: BusEvent.define(
     "message.part.delta",
-    z.object({
-      sessionID: SessionID.zod,
-      messageID: MessageID.zod,
-      partID: PartID.zod,
-      field: z.string(),
-      delta: z.string(),
+    Schema.Struct({
+      sessionID: SessionID,
+      messageID: MessageID,
+      partID: PartID,
+      field: Schema.String,
+      delta: Schema.String,
     }),
   ),
   PartRemoved: SyncEvent.define({
diff --git a/packages/opencode/src/session/session.ts b/packages/opencode/src/session/session.ts
index 1e046fdf79..f4fe3bf8bd 100644
--- a/packages/opencode/src/session/session.ts
+++ b/packages/opencode/src/session/session.ts
@@ -273,17 +273,18 @@ export const Event = {
   }),
   Diff: BusEvent.define(
     "session.diff",
-    z.object({
-      sessionID: SessionID.zod,
-      diff: Snapshot.FileDiff.zod.array(),
+    Schema.Struct({
+      sessionID: SessionID,
+      diff: Schema.Array(Snapshot.FileDiff),
     }),
   ),
   Error: BusEvent.define(
     "session.error",
-    z.object({
-      sessionID: SessionID.zod.optional(),
-      // z.lazy defers access to break circular dep: session → message-v2 → provider → plugin → session
-      error: z.lazy(() => (MessageV2.Assistant.zod as unknown as z.ZodObject<any>).shape.error),
+    Schema.Struct({
+      sessionID: Schema.optional(SessionID),
+      // Reuses MessageV2.Assistant.fields.error (already Schema.optional) so
+      // the derived zod keeps the same discriminated-union shape on the bus.
+      error: MessageV2.Assistant.fields.error,
     }),
   ),
 }
diff --git a/packages/opencode/src/session/status.ts b/packages/opencode/src/session/status.ts
index b9b9fd7e74..e5165a7879 100644
--- a/packages/opencode/src/session/status.ts
+++ b/packages/opencode/src/session/status.ts
@@ -28,16 +28,16 @@ export type Info = Schema.Schema.Type<typeof Info>
 export const Event = {
   Status: BusEvent.define(
     "session.status",
-    z.object({
-      sessionID: SessionID.zod,
-      status: Info.zod,
+    Schema.Struct({
+      sessionID: SessionID,
+      status: Info,
     }),
   ),
   // deprecated
   Idle: BusEvent.define(
     "session.idle",
-    z.object({
-      sessionID: SessionID.zod,
+    Schema.Struct({
+      sessionID: SessionID,
     }),
   ),
 }
diff --git a/packages/opencode/src/session/todo.ts b/packages/opencode/src/session/todo.ts
index 257b586ed7..c3a9b106b1 100644
--- a/packages/opencode/src/session/todo.ts
+++ b/packages/opencode/src/session/todo.ts
@@ -22,9 +22,9 @@ export type Info = Schema.Schema.Type<typeof Info>
 export const Event = {
   Updated: BusEvent.define(
     "todo.updated",
-    z.object({
-      sessionID: SessionID.zod,
-      todos: z.array(Info.zod),
+    Schema.Struct({
+      sessionID: SessionID,
+      todos: Schema.Array(Info),
     }),
   ),
 }
diff --git a/packages/opencode/src/sync/index.ts b/packages/opencode/src/sync/index.ts
index 482ad4fbb6..35a5abd0b1 100644
--- a/packages/opencode/src/sync/index.ts
+++ b/packages/opencode/src/sync/index.ts
@@ -8,51 +8,48 @@ import { EventSequenceTable, EventTable } from "./event.sql"
 import { WorkspaceContext } from "@/control-plane/workspace-context"
 import { EventID } from "./schema"
 import { Flag } from "@/flag/flag"
-import { Schema as EffectSchema, Types } from "effect"
+import { Schema as EffectSchema } from "effect"
 import { zodObject } from "@/util/effect-zod"
-import { isRecord } from "@/util/record"
+import type { DeepMutable } from "@/util/schema"
+
+// Keep `Event["data"]` mutable because projectors mutate the persisted shape
+// when writing to the database. Bus payloads (`Properties`) stay readonly —
+// subscribers only read.
 
 export type Definition<
+  Type extends string = string,
   Schema extends EffectSchema.Top = EffectSchema.Top,
   BusSchema extends EffectSchema.Top = Schema,
 > = {
-  type: string
+  type: Type
   version: number
   aggregate: string
-  effectSchema: Schema
-  effectProperties: BusSchema
-  schema: z.ZodObject
-
-  // This is temporary and only exists for compatibility with bus
-  // event definitions
-  properties: z.ZodObject
+  schema: Schema
+  // Bus event payload schema. Defaults to `schema` unless `busSchema` was
+  // passed at definition time (see `session.updated`, whose projector
+  // expands the persisted data to a `{ sessionID, info }` bus payload).
+  properties: BusSchema
 }
 
 export type Event<Def extends Definition = Definition> = {
   id: string
   seq: number
   aggregateID: string
-  data: Types.DeepMutable<EffectSchema.Schema.Type<Def["effectSchema"]>>
+  data: DeepMutable<EffectSchema.Schema.Type<Def["schema"]>>
 }
 
-export type Properties<Def extends Definition = Definition> = Types.DeepMutable<
-  EffectSchema.Schema.Type<Def["effectProperties"]>
->
+export type Properties<Def extends Definition = Definition> = EffectSchema.Schema.Type<Def["properties"]>
 
 export type SerializedEvent<Def extends Definition = Definition> = Event<Def> & { type: string }
 
 type ProjectorFunc = (db: Database.TxOrDb, data: unknown) => void
+type ConvertEvent = (type: string, data: Event["data"]) => unknown | Promise<unknown>
 
 export const registry = new Map<string, Definition>()
 let projectors: Map<Definition, ProjectorFunc> | undefined
 const versions = new Map<string, number>()
 let frozen = false
-let convertEvent: (type: string, event: Event["data"]) => Promise<unknown> | unknown
-
-function asRecord(input: unknown) {
-  if (isRecord(input)) return input
-  throw new Error(`SyncEvent.convertEvent must return an object, got: ${JSON.stringify(input)}`)
-}
+let convertEvent: ConvertEvent
 
 export function reset() {
   frozen = false
@@ -60,7 +57,7 @@ export function reset() {
   convertEvent = (_, data) => data
 }
 
-export function init(input: { projectors: Array<[Definition, ProjectorFunc]>; convertEvent?: typeof convertEvent }) {
+export function init(input: { projectors: Array<[Definition, ProjectorFunc]>; convertEvent?: ConvertEvent }) {
   projectors = new Map(input.projectors)
 
   // Install all the latest event defs to the bus. We only ever emit
@@ -76,7 +73,7 @@ export function init(input: { projectors: Array<[Definition, ProjectorFunc]>; co
   // Freeze the system so it clearly errors if events are defined
   // after `init` which would cause bugs
   frozen = true
-  convertEvent = input.convertEvent || ((_, data) => data)
+  convertEvent = input.convertEvent ?? ((_, data) => data)
 }
 
 export function versionedType<A extends string>(type: A): A
@@ -96,21 +93,17 @@ export function define<
   aggregate: Agg
   schema: Schema
   busSchema?: BusSchema
-}): Definition<Schema, BusSchema> {
+}): Definition<Type, Schema, BusSchema> {
   if (frozen) {
     throw new Error("Error defining sync event: sync system has been frozen")
   }
 
-  const effectProperties = (input.busSchema ?? input.schema) as BusSchema
-
   const def = {
     type: input.type,
     version: input.version,
     aggregate: input.aggregate,
-    effectSchema: input.schema,
-    effectProperties,
-    schema: zodObject(input.schema),
-    properties: zodObject(effectProperties),
+    schema: input.schema,
+    properties: (input.busSchema ?? input.schema) as BusSchema,
   }
 
   versions.set(def.type, Math.max(def.version, versions.get(def.type) || 0))
@@ -167,12 +160,11 @@ function process<Def extends Definition>(def: Def, event: Event<Def>, options: {
     Database.effect(() => {
       if (options?.publish) {
         const result = convertEvent(def.type, event.data)
+        const publish = (data: unknown) => ProjectBus.publish(def, data as Properties<Def>)
         if (result instanceof Promise) {
-          void result.then((data) => {
-            void ProjectBus.publish({ type: def.type, properties: def.properties }, asRecord(data))
-          })
+          void result.then(publish)
         } else {
-          void ProjectBus.publish({ type: def.type, properties: def.properties }, asRecord(result))
+          void publish(result)
         }
 
         GlobalBus.emit("event", {
@@ -292,7 +284,7 @@ export function payloads() {
           id: z.string(),
           seq: z.number(),
           aggregateID: z.literal(def.aggregate),
-          data: def.schema,
+          data: zodObject(def.schema),
         })
         .meta({
           ref: `SyncEvent.${def.type}`,
diff --git a/packages/opencode/src/util/effect-zod.ts b/packages/opencode/src/util/effect-zod.ts
index edbbf4d542..24ff9a10e1 100644
--- a/packages/opencode/src/util/effect-zod.ts
+++ b/packages/opencode/src/util/effect-zod.ts
@@ -59,8 +59,17 @@ function walk(ast: SchemaAST.AST): z.ZodTypeAny {
 
 function walkUncached(ast: SchemaAST.AST): z.ZodTypeAny {
   const override = (ast.annotations as any)?.[ZodOverride] as z.ZodTypeAny | undefined
-  if (override) return override
+  // `description` annotations layer on top of an override so callers can
+  // reuse a shared override schema (e.g. `SessionID`) and still add a
+  // per-field description on the outer wrapper.
+  const base = override ?? bodyWithChecks(ast)
+  const desc = SchemaAST.resolveDescription(ast)
+  const ref = SchemaAST.resolveIdentifier(ast)
+  const described = desc ? base.describe(desc) : base
+  return ref ? described.meta({ ref }) : described
+}
 
+function bodyWithChecks(ast: SchemaAST.AST): z.ZodTypeAny {
   // Schema.Class wraps its fields in a Declaration AST plus an encoding that
   // constructs the class instance. For the Zod derivation we want the plain
   // field shape (the decoded/consumer view), not the class instance — so
@@ -74,11 +83,7 @@ function walkUncached(ast: SchemaAST.AST): z.ZodTypeAny {
   const hasEncoding = ast.encoding?.length && ast._tag !== "Declaration"
   const hasTransform = hasEncoding && !(SchemaAST.isOptional(ast) && extractDefault(ast) !== undefined)
   const base = hasTransform ? encoded(ast) : body(ast)
-  const checked = ast.checks?.length ? applyChecks(base, ast.checks, ast) : base
-  const desc = SchemaAST.resolveDescription(ast)
-  const ref = SchemaAST.resolveIdentifier(ast)
-  const described = desc ? checked.describe(desc) : checked
-  return ref ? described.meta({ ref }) : described
+  return ast.checks?.length ? applyChecks(base, ast.checks, ast) : base
 }
 
 // Walk the encoded side and apply each link's decode to produce the decoded
diff --git a/packages/opencode/src/util/schema.ts b/packages/opencode/src/util/schema.ts
index 7f94ee5d1e..0c50482bbd 100644
--- a/packages/opencode/src/util/schema.ts
+++ b/packages/opencode/src/util/schema.ts
@@ -10,6 +10,34 @@ export const PositiveInt = Schema.Int.check(Schema.isGreaterThan(0))
  */
 export const NonNegativeInt = Schema.Int.check(Schema.isGreaterThanOrEqualTo(0))
 
+/**
+ * Strip `readonly` from a nested type. Stand-in for `effect`'s `Types.DeepMutable`
+ * until `effect:core/x228my` ("Types.DeepMutable widens unknown to `{}`") lands.
+ *
+ * The upstream version falls through `unknown` into `{ -readonly [K in keyof T]: ... }`
+ * where `keyof unknown = never`, so `unknown` collapses to `{}`. This local
+ * version gates the object branch on `extends object` (which `unknown` does
+ * not) so `unknown` passes through untouched.
+ *
+ * Primitive bailout matches upstream — without it, branded strings like
+ * `string & Brand<"SessionID">` fall into the object branch and get their
+ * prototype methods walked.
+ *
+ * Tuple branch preserves readonly tuples (e.g. `ConfigPlugin.Spec`'s
+ * `readonly [string, Options]`); the general array branch would otherwise
+ * widen them to unbounded arrays.
+ */
+// eslint-disable-next-line @typescript-eslint/ban-types
+export type DeepMutable<T> = T extends string | number | boolean | bigint | symbol | Function
+  ? T
+  : T extends readonly [unknown, ...unknown[]]
+    ? { -readonly [K in keyof T]: DeepMutable<T[K]> }
+    : T extends readonly (infer U)[]
+      ? DeepMutable<U>[]
+      : T extends object
+        ? { -readonly [K in keyof T]: DeepMutable<T[K]> }
+        : T
+
 /**
  * Attach static methods to a schema object. Designed to be used with `.pipe()`:
  *
@@ -26,13 +54,16 @@ export const withStatics =
   (schema: S): S & M =>
     Object.assign(schema, methods(schema))
 
-declare const NewtypeBrand: unique symbol
-type NewtypeBrand<Tag extends string> = { readonly [NewtypeBrand]: Tag }
-
 /**
  * Nominal wrapper for scalar types. The class itself is a valid schema —
  * pass it directly to `Schema.decode`, `Schema.decodeEffect`, etc.
  *
+ * Overrides `~type.make` on the derived `Schema.Opaque` so `Schema.Schema.Type`
+ * of a field using this newtype resolves to `Self` rather than the underlying
+ * branded phantom. Without that override, passing a class instance to code
+ * typed against `Schema.Schema.Type<FieldSchema>` would require a cast even
+ * though the values are structurally equivalent at runtime.
+ *
  * @example
  *   class QuestionID extends Newtype<QuestionID>()("QuestionID", Schema.String) {
  *     static make(id: string): QuestionID {
@@ -44,10 +75,8 @@ type NewtypeBrand<Tag extends string> = { readonly [NewtypeBrand]: Tag }
  */
 export function Newtype<Self>() {
   return <const Tag extends string, S extends Schema.Top>(tag: Tag, schema: S) => {
-    type Branded = NewtypeBrand<Tag>
-
     abstract class Base {
-      declare readonly [NewtypeBrand]: Tag
+      declare readonly _newtype: Tag
 
       static make(value: Schema.Schema.Type<S>): Self {
         return value as unknown as Self
@@ -56,8 +85,10 @@ export function Newtype<Self>() {
 
     Object.setPrototypeOf(Base, schema)
 
-    return Base as unknown as (abstract new (_: never) => Branded) & {
+    return Base as unknown as (abstract new (_: never) => { readonly _newtype: Tag }) & {
       readonly make: (value: Schema.Schema.Type<S>) => Self
-    } & Omit<Schema.Opaque<Self, S, {}>, "make">
+    } & Omit<Schema.Opaque<Self, S, {}>, "make" | "~type.make"> & {
+        readonly "~type.make": Self
+      }
   }
 }
diff --git a/packages/opencode/src/worktree/index.ts b/packages/opencode/src/worktree/index.ts
index bbebeaa496..e122fe453b 100644
--- a/packages/opencode/src/worktree/index.ts
+++ b/packages/opencode/src/worktree/index.ts
@@ -13,7 +13,7 @@ import { errorMessage } from "../util/error"
 import { BusEvent } from "@/bus/bus-event"
 import { GlobalBus } from "@/bus/global"
 import { Git } from "@/git"
-import { Effect, Layer, Path, Scope, Context, Stream } from "effect"
+import { Effect, Layer, Path, Schema, Scope, Context, Stream } from "effect"
 import { ChildProcess, ChildProcessSpawner } from "effect/unstable/process"
 import { NodePath } from "@effect/platform-node"
 import { AppFileSystem } from "@opencode-ai/shared/filesystem"
@@ -26,15 +26,15 @@ const log = Log.create({ service: "worktree" })
 export const Event = {
   Ready: BusEvent.define(
     "worktree.ready",
-    z.object({
-      name: z.string(),
-      branch: z.string(),
+    Schema.Struct({
+      name: Schema.String,
+      branch: Schema.String,
     }),
   ),
   Failed: BusEvent.define(
     "worktree.failed",
-    z.object({
-      message: z.string(),
+    Schema.Struct({
+      message: Schema.String,
     }),
   ),
 }
diff --git a/packages/opencode/test/bus/bus-effect.test.ts b/packages/opencode/test/bus/bus-effect.test.ts
index 6f96a89c87..3d602ae6fd 100644
--- a/packages/opencode/test/bus/bus-effect.test.ts
+++ b/packages/opencode/test/bus/bus-effect.test.ts
@@ -1,6 +1,5 @@
 import { describe, expect } from "bun:test"
-import { Deferred, Effect, Layer, Stream } from "effect"
-import z from "zod"
+import { Deferred, Effect, Layer, Schema, Stream } from "effect"
 import { Bus } from "../../src/bus"
 import { BusEvent } from "../../src/bus/bus-event"
 import { Instance } from "../../src/project/instance"
@@ -9,8 +8,8 @@ import { provideInstance, provideTmpdirInstance, tmpdirScoped } from "../fixture
 import { testEffect } from "../lib/effect"
 
 const TestEvent = {
-  Ping: BusEvent.define("test.effect.ping", z.object({ value: z.number() })),
-  Pong: BusEvent.define("test.effect.pong", z.object({ message: z.string() })),
+  Ping: BusEvent.define("test.effect.ping", Schema.Struct({ value: Schema.Number })),
+  Pong: BusEvent.define("test.effect.pong", Schema.Struct({ message: Schema.String })),
 }
 
 const node = CrossSpawnSpawner.defaultLayer
diff --git a/packages/opencode/test/bus/bus-integration.test.ts b/packages/opencode/test/bus/bus-integration.test.ts
index e42bd5299e..2808344577 100644
--- a/packages/opencode/test/bus/bus-integration.test.ts
+++ b/packages/opencode/test/bus/bus-integration.test.ts
@@ -1,11 +1,11 @@
 import { afterEach, describe, expect, test } from "bun:test"
-import z from "zod"
+import { Schema } from "effect"
 import { Bus } from "../../src/bus"
 import { BusEvent } from "../../src/bus/bus-event"
 import { Instance } from "../../src/project/instance"
 import { tmpdir } from "../fixture/fixture"
 
-const TestEvent = BusEvent.define("test.integration", z.object({ value: z.number() }))
+const TestEvent = BusEvent.define("test.integration", Schema.Struct({ value: Schema.Number }))
 
 function withInstance(directory: string, fn: () => Promise<void>) {
   return Instance.provide({ directory, fn })
@@ -42,7 +42,7 @@ describe("Bus integration: acquireRelease subscriber pattern", () => {
     await using tmp = await tmpdir()
     const received: Array<{ type: string; value?: number }> = []
 
-    const OtherEvent = BusEvent.define("test.other", z.object({ value: z.number() }))
+    const OtherEvent = BusEvent.define("test.other", Schema.Struct({ value: Schema.Number }))
 
     await withInstance(tmp.path, async () => {
       Bus.subscribeAll((evt) => {
diff --git a/packages/opencode/test/bus/bus.test.ts b/packages/opencode/test/bus/bus.test.ts
index 3df179787d..cdacdd5179 100644
--- a/packages/opencode/test/bus/bus.test.ts
+++ b/packages/opencode/test/bus/bus.test.ts
@@ -1,13 +1,13 @@
 import { afterEach, describe, expect, test } from "bun:test"
-import z from "zod"
+import { Schema } from "effect"
 import { Bus } from "../../src/bus"
 import { BusEvent } from "../../src/bus/bus-event"
 import { Instance } from "../../src/project/instance"
 import { tmpdir } from "../fixture/fixture"
 
 const TestEvent = {
-  Ping: BusEvent.define("test.ping", z.object({ value: z.number() })),
-  Pong: BusEvent.define("test.pong", z.object({ message: z.string() })),
+  Ping: BusEvent.define("test.ping", Schema.Struct({ value: Schema.Number })),
+  Pong: BusEvent.define("test.pong", Schema.Struct({ message: Schema.String })),
 }
 
 function withInstance(directory: string, fn: () => Promise<void>) {
diff --git a/packages/opencode/test/session/session.test.ts b/packages/opencode/test/session/session.test.ts
index f63ad9beed..d4a1d711d8 100644
--- a/packages/opencode/test/session/session.test.ts
+++ b/packages/opencode/test/session/session.test.ts
@@ -111,9 +111,12 @@ describe("step-finish token propagation via Bus event", () => {
             mode: "",
           } as unknown as MessageV2.Info)
 
+          // Bus subscribers receive readonly Schema.Type payloads; `MessageV2.Part`
+          // is the mutable domain type. Cast bridges the two — safe because the
+          // test only reads the value afterwards.
           let received: MessageV2.Part | undefined
           const unsub = Bus.subscribe(MessageV2.Event.PartUpdated, (event) => {
-            received = event.properties.part
+            received = event.properties.part as MessageV2.Part
           })
 
           const tokens = {