fix(team-mode): refactor layout to use testable spawn-process helper

The existing layout.test.ts relied on mock.module("bun", ...) registered
at the top level, but test-setup.ts calls mock.restore() + restoreModuleMocks()
in afterEach, so every test except the first one lost its mocks. CI has
been red on this file since e303feef.

Two changes:

1. layout.ts now imports spawn from the existing spawn-process helper
   instead of "bun" directly, matching the pattern established for
   closeTmuxPane and killTmuxSessionIfExists. This does not change
   runtime behavior - spawn-process just re-exports Bun's spawn.

2. layout.test.ts registers module mocks inside beforeEach and uses the
   ?test=UUID cache-busting dynamic-import pattern so the mocks apply
   on every test run, not just the first.

All 4 layout.test.ts cases now pass.

src/features/team-mode/team-layout-tmux/layout.test.ts

@@ -1,21 +1,32 @@
 import { beforeEach, describe, expect, mock, test } from "bun:test"
 
+type LayoutModule = typeof import("./layout")
+
 const spawnMock = mock(() => ({
   exited: Promise.resolve(0),
   stdout: new ReadableStream({ start(controller) { controller.enqueue(new TextEncoder().encode("%1\n")); controller.close() } }),
   stderr: new ReadableStream({ start(controller) { controller.close() } }),
 }))
 
-mock.module("bun", () => ({ spawn: spawnMock }))
+const layoutSpecifier = import.meta.resolve("./layout")
+const spawnProcessSpecifier = import.meta.resolve("../../../shared/tmux/tmux-utils/spawn-process")
+const tmuxPathResolverSpecifier = import.meta.resolve("../../../tools/interactive-bash/tmux-path-resolver")
+const sharedSpecifier = import.meta.resolve("../../../shared")
 
-mock.module("../../../tools/interactive-bash/tmux-path-resolver", () => ({ getTmuxPath: mock(() => Promise.resolve("tmux")) }))
+function registerModuleMocks(): void {
+  mock.module(spawnProcessSpecifier, () => ({ spawn: spawnMock }))
+  mock.module(tmuxPathResolverSpecifier, () => ({ getTmuxPath: mock(() => Promise.resolve("tmux")) }))
+  mock.module(sharedSpecifier, () => ({ log: mock(() => undefined) }))
+}
 
-mock.module("../../../shared", () => ({ log: mock(() => undefined) }))
-
-import { createTeamLayout, removeTeamLayout, canVisualize } from "./layout"
+async function loadLayoutModule(): Promise<LayoutModule> {
+  const module = await import(`${layoutSpecifier}?test=${crypto.randomUUID()}`)
+  return module as LayoutModule
+}
 
 describe("team-layout-tmux", () => {
   beforeEach(() => {
+    registerModuleMocks()
     spawnMock.mockClear()
     process.env.TMUX = "/tmp/tmux-1"
   })
@@ -23,6 +34,7 @@ describe("team-layout-tmux", () => {
   test("returns null and makes no tmux calls when visualization unavailable", async () => {
     // given
     delete process.env.TMUX
+    const { createTeamLayout, canVisualize } = await loadLayoutModule()
 
     // when
     const result = await createTeamLayout("run-1", [], {} as never)
@@ -35,6 +47,7 @@ describe("team-layout-tmux", () => {
 
   test("creates focus and grid windows", async () => {
     // given
+    const { createTeamLayout } = await loadLayoutModule()
     const members = [
       { name: "lead", sessionId: "s1", color: "red" },
       { name: "m2", sessionId: "s2" },
@@ -54,6 +67,7 @@ describe("team-layout-tmux", () => {
 
   test("returns null when tmux command fails", async () => {
     // given
+    const { createTeamLayout } = await loadLayoutModule()
     spawnMock.mockImplementationOnce(() => ({
       exited: Promise.resolve(1),
       stdout: new ReadableStream({ start(controller) { controller.close() } }),
@@ -69,6 +83,8 @@ describe("team-layout-tmux", () => {
 
   test("cleans up the tmux session", async () => {
     // given
+    const { removeTeamLayout } = await loadLayoutModule()
+
     // when
     await removeTeamLayout("run-4", {} as never)
 

src/features/team-mode/team-layout-tmux/layout.ts

@@ -1,4 +1,4 @@
-import { spawn } from "bun"
+import { spawn } from "../../../shared/tmux/tmux-utils/spawn-process"
 import { log } from "../../../shared"
 import { getTmuxPath } from "../../../tools/interactive-bash/tmux-path-resolver"
 import type { TmuxSessionManager } from "../../tmux-subagent/manager"