feat(tui): support fake renderer in simulation mode

- OPENCODE_SIMULATION_RENDERER=fake creates an OpenTUI test renderer
  (in-memory screen buffer) instead of the terminal renderer; size via
  OPENCODE_SIMULATION_TUI_WIDTH/HEIGHT
- Harness carries mockInput/mockMouse and prefers TestRendererSetup
  APIs (captureCharFrame, renderOnce) over the private
  currentRenderBuffer fallback used for the visible renderer
- Fix Bun.Server generic type argument in simulation server

packages/tui/src/app.tsx

@@ -8,7 +8,8 @@ import { ClipboardProvider, useClipboard } from "./context/clipboard"
 import { ExitProvider, useExit } from "./context/exit"
 import { EpilogueProvider } from "./context/epilogue"
 import * as Selection from "./util/selection"
-import { createCliRenderer, MouseButton } from "@opentui/core"
+import { createCliRenderer, MouseButton, type CliRenderer } from "@opentui/core"
+import type { TestRendererSetup } from "@opentui/core/testing"
 import { RouteProvider, useRoute } from "./context/route"
 import {
   Switch,
@@ -180,12 +181,24 @@ function isVersionGreater(left: string, right: string) {
 export const run = Effect.fn("Tui.run")(function* (input: TuiInput) {
   const global = yield* Global.Service
   const exit = { epilogue: undefined as string | undefined, reason: undefined as unknown }
+  const simulationEnabled = process.env.OPENCODE_SIMULATION === "1" || process.env.OPENCODE_SIMULATION === "true"
   const result = yield* Effect.scoped(
     Effect.gen(function* () {
-      const renderer = yield* Effect.acquireRelease(
+      const acquired = yield* Effect.acquireRelease(
         Effect.tryPromise({
-          try: () =>
-            createCliRenderer({
+          try: async (): Promise<{ renderer: CliRenderer; setup?: TestRendererSetup }> => {
+            // The fake renderer is a real CliRenderer backed by an in-memory
+            // screen buffer; everything downstream (keymap, harness, render)
+            // treats both renderer kinds identically.
+            if (simulationEnabled && process.env.OPENCODE_SIMULATION_RENDERER === "fake") {
+              const { createTestRenderer } = await import("@opentui/core/testing")
+              const setup = await createTestRenderer({
+                width: Number(process.env.OPENCODE_SIMULATION_TUI_WIDTH) || 100,
+                height: Number(process.env.OPENCODE_SIMULATION_TUI_HEIGHT) || 40,
+              })
+              return { renderer: setup.renderer, setup }
+            }
+            const renderer = await createCliRenderer({
               externalOutputMode: "passthrough",
               targetFps: 60,
               gatherStats: false,
@@ -197,14 +210,17 @@ export const run = Effect.fn("Tui.run")(function* (input: TuiInput) {
               consoleOptions: {
                 keyBindings: [{ name: "y", ctrl: true, action: "copy-selection" }],
               },
-            }),
+            })
+            return { renderer }
+          },
           catch: (error) => (error instanceof Error ? error : new Error(String(error))),
         }),
-        (renderer) =>
+        (acquired) =>
           Effect.sync(() => {
-            destroyRenderer(renderer)
+            destroyRenderer(acquired.renderer)
           }),
       )
+      const renderer = acquired.renderer
       win32DisableProcessedInput()
       const keymap = createDefaultOpenTuiKeymap(renderer)
       yield* Effect.acquireRelease(
@@ -230,15 +246,16 @@ export const run = Effect.fn("Tui.run")(function* (input: TuiInput) {
       renderer.once("destroy", () => Deferred.doneUnsafe(shutdown, Effect.void))
       const pluginRuntime = createPluginRuntime()
 
-      const simulation = yield* Effect.promise(async () => {
-        if (process.env.OPENCODE_SIMULATION !== "1" && process.env.OPENCODE_SIMULATION !== "true") return
-        const { SimulationActions } = await import("./simulation/actions")
-        const { SimulationServer } = await import("./simulation/server")
-        return SimulationServer.start(SimulationActions.createHarness(renderer))
-      })
-      if (simulation) {
-        process.stderr.write(`opencode simulation websocket: ${simulation.url}\n`)
-        yield* Effect.addFinalizer(() => Effect.sync(() => simulation.stop()))
+      if (simulationEnabled) {
+        const simulation = yield* Effect.promise(async () => {
+          const { SimulationActions } = await import("./simulation/actions")
+          const { SimulationServer } = await import("./simulation/server")
+          return SimulationServer.start(SimulationActions.createHarness(renderer, acquired.setup))
+        })
+        if (simulation) {
+          process.stderr.write(`opencode simulation websocket: ${simulation.url}\n`)
+          yield* Effect.addFinalizer(() => Effect.sync(() => simulation.stop()))
+        }
       }
 
       yield* Effect.tryPromise(async () => {

packages/tui/src/simulation/actions.ts

@@ -1,5 +1,11 @@
 import type { CliRenderer, Renderable } from "@opentui/core"
-import { createMockKeys, createMockMouse } from "@opentui/core/testing"
+import {
+  createMockKeys,
+  createMockMouse,
+  type MockInput,
+  type MockMouse,
+  type TestRendererSetup,
+} from "@opentui/core/testing"
 import { SimulationTrace } from "./trace"
 
 export interface KeyModifiers {
@@ -33,6 +39,8 @@ export interface Element {
 
 export interface Harness {
   readonly renderer: CliRenderer
+  readonly mockInput: MockInput
+  readonly mockMouse: MockMouse
   readonly renderOnce: () => Promise<void>
   readonly screen: () => string
 }
@@ -66,14 +74,28 @@ function hit(renderer: CliRenderer, renderable: Renderable) {
   return renderer.hitTest(x, y) === renderable.num
 }
 
-export function createHarness(renderer: CliRenderer): Harness {
+/**
+ * Builds the harness the simulation server drives.
+ *
+ * When the renderer came from `createTestRenderer` (fake renderer), pass its
+ * `TestRendererSetup` so the harness uses the supported testing APIs. Without
+ * it (visible terminal renderer) the harness falls back to `requestRender` +
+ * `idle` and reading the private `currentRenderBuffer`.
+ */
+export function createHarness(renderer: CliRenderer, setup?: TestRendererSetup): Harness {
   return {
     renderer,
-    renderOnce: async () => {
-      renderer.requestRender()
-      await renderer.idle()
-    },
-    screen: () => decoder.decode((Reflect.get(renderer, "currentRenderBuffer") as RenderBuffer).getRealCharBytes(true)),
+    mockInput: setup?.mockInput ?? createMockKeys(renderer),
+    mockMouse: setup?.mockMouse ?? createMockMouse(renderer),
+    renderOnce:
+      setup?.renderOnce ??
+      (async () => {
+        renderer.requestRender()
+        await renderer.idle()
+      }),
+    screen:
+      setup?.captureCharFrame ??
+      (() => decoder.decode((Reflect.get(renderer, "currentRenderBuffer") as RenderBuffer).getRealCharBytes(true))),
   }
 }
 
@@ -131,27 +153,25 @@ export function state(harness: Harness) {
 }
 
 export async function execute(harness: Harness, action: Action) {
-  const mockInput = createMockKeys(harness.renderer)
-  const mockMouse = createMockMouse(harness.renderer)
   SimulationTrace.add("ui.action", { action })
   switch (action.type) {
     case "typeText":
-      await mockInput.typeText(action.text)
+      await harness.mockInput.typeText(action.text)
       break
     case "pressKey":
-      mockInput.pressKey(action.key, action.modifiers)
+      harness.mockInput.pressKey(action.key, action.modifiers)
       break
     case "pressEnter":
-      mockInput.pressEnter()
+      harness.mockInput.pressEnter()
       break
     case "pressArrow":
-      mockInput.pressArrow(action.direction)
+      harness.mockInput.pressArrow(action.direction)
       break
     case "focus":
       all(harness.renderer.root).find((item) => item.num === action.target)?.focus()
       break
     case "click":
-      await mockMouse.click(action.x, action.y)
+      await harness.mockMouse.click(action.x, action.y)
       break
   }
   await harness.renderOnce()

packages/tui/src/simulation/server.ts

@@ -118,7 +118,11 @@ async function handle(harness: Harness, request: JsonRpcRequest) {
   throw new Error(`Unknown simulation method: ${request.method}`)
 }
 
-function serve(harness: Harness, port = DefaultPort, attempts = MaxPortAttempts): Bun.Server {
+function serve(
+  harness: Harness,
+  port = DefaultPort,
+  attempts = MaxPortAttempts,
+): Bun.Server<{ readonly simulation: true }> {
   try {
     return Bun.serve<{ readonly simulation: true }>({
       hostname: "127.0.0.1",