diff --git a/packages/opencode/src/server/routes/instance/httpapi/handlers/tui.ts b/packages/opencode/src/server/routes/instance/httpapi/handlers/tui.ts
index cb12ccb7a7..c7c447ce85 100644
--- a/packages/opencode/src/server/routes/instance/httpapi/handlers/tui.ts
+++ b/packages/opencode/src/server/routes/instance/httpapi/handlers/tui.ts
@@ -28,8 +28,8 @@ const commandAliases = {
 export const tuiHandlers = HttpApiBuilder.group(InstanceHttpApi, "tui", (handlers) =>
   Effect.gen(function* () {
     const bus = yield* Bus.Service
-    const publishCommand = (command: typeof TuiEvent.CommandExecute.properties.Type.command) =>
-      bus.publish(TuiEvent.CommandExecute, { command })
+    const publishCommand = (command: typeof TuiEvent.CommandExecute.properties.Type.command | undefined) =>
+      bus.publish(TuiEvent.CommandExecute, { command } as typeof TuiEvent.CommandExecute.properties.Type)
 
     const appendPrompt = Effect.fn("TuiHttpApi.appendPrompt")(function* (ctx: {
       payload: typeof TuiEvent.PromptAppend.properties.Type
@@ -71,7 +71,8 @@ export const tuiHandlers = HttpApiBuilder.group(InstanceHttpApi, "tui", (handler
     const executeCommand = Effect.fn("TuiHttpApi.executeCommand")(function* (ctx: {
       payload: typeof CommandPayload.Type
     }) {
-      yield* publishCommand(commandAliases[ctx.payload.command as keyof typeof commandAliases] ?? ctx.payload.command)
+      // Legacy only publishes known aliases; unknown commands become undefined.
+      yield* publishCommand(commandAliases[ctx.payload.command as keyof typeof commandAliases])
       return true
     })
 
diff --git a/packages/opencode/test/server/httpapi-tui.test.ts b/packages/opencode/test/server/httpapi-tui.test.ts
index 9f7c8e9e89..3e844fad02 100644
--- a/packages/opencode/test/server/httpapi-tui.test.ts
+++ b/packages/opencode/test/server/httpapi-tui.test.ts
@@ -1,6 +1,8 @@
 import { afterEach, describe, expect, test } from "bun:test"
 import type { Context } from "hono"
 import { Flag } from "@opencode-ai/core/flag/flag"
+import { GlobalBus } from "../../src/bus/global"
+import { TuiEvent } from "../../src/cli/cmd/tui/event"
 import { SessionID } from "../../src/session/schema"
 import { Instance } from "../../src/project/instance"
 import { TuiApi, TuiPaths } from "../../src/server/routes/instance/httpapi/groups/tui"
@@ -15,9 +17,20 @@ void Log.init({ print: false })
 
 const original = Flag.OPENCODE_EXPERIMENTAL_HTTPAPI
 
-function app() {
-  Flag.OPENCODE_EXPERIMENTAL_HTTPAPI = true
-  return Server.Default().app
+function app(experimental = true) {
+  Flag.OPENCODE_EXPERIMENTAL_HTTPAPI = experimental
+  return experimental ? Server.Default().app : Server.Legacy().app
+}
+
+function nextCommandExecute() {
+  return new Promise<unknown>((resolve) => {
+    const listener = (event: { payload: { type?: string; properties?: { command?: unknown } } }) => {
+      if (event.payload.type !== TuiEvent.CommandExecute.type) return
+      GlobalBus.off("event", listener)
+      resolve(event.payload.properties?.command)
+    }
+    GlobalBus.on("event", listener)
+  })
 }
 
 async function expectTrue(path: string, headers: Record<string, string>, body?: unknown) {
@@ -72,6 +85,27 @@ describe("tui HttpApi bridge", () => {
     expect(missing.status).toBe(404)
   })
 
+  test("matches legacy unknown execute command behavior", async () => {
+    await using tmp = await tmpdir({ git: true, config: { formatter: false, lsp: false } })
+    const headers = { "x-opencode-directory": tmp.path, "content-type": "application/json" }
+    const body = JSON.stringify({ command: "unknown_command" })
+
+    const legacyCommand = nextCommandExecute()
+    const legacy = await app(false).request(TuiPaths.executeCommand, { method: "POST", headers, body })
+    expect(legacy.status).toBe(200)
+    expect(await legacy.json()).toBe(true)
+
+    const effectCommand = nextCommandExecute()
+    const effect = await app().request(TuiPaths.executeCommand, { method: "POST", headers, body })
+    expect(effect.status).toBe(200)
+    expect(await effect.json()).toBe(true)
+
+    const legacyPublished = await legacyCommand
+    const effectPublished = await effectCommand
+    expect(effectPublished).toBe(legacyPublished)
+    expect(legacyPublished).toBeUndefined()
+  })
+
   test("serves TUI control queue through experimental Effect routes", async () => {
     await using tmp = await tmpdir({ git: true, config: { formatter: false, lsp: false } })
     const pending = callTui({ req: { json: async () => ({ value: 1 }), path: "/demo" } } as unknown as Context)