diff --git a/src/main/ipc/pty/runtime/spawn-preflight-wsl-background-hold.test.ts b/src/main/ipc/pty/runtime/spawn-preflight-wsl-background-hold.test.ts
index 738631fbfec..2e1be2667e9 100644
--- a/src/main/ipc/pty/runtime/spawn-preflight-wsl-background-hold.test.ts
+++ b/src/main/ipc/pty/runtime/spawn-preflight-wsl-background-hold.test.ts
@@ -4,6 +4,7 @@ import { wslDistroHoldMessage } from '../../../../shared/wsl-distro-stopped-hold
 import { prepareRuntimePtySpawn } from './spawn-preflight'
 import { createRuntimePtySpawnState, type RuntimePtySpawnArgs } from './spawn-state'
 import { makeRuntimePtySpawnTestDeps } from './spawn-preflight-test-deps-fixture'
+import { isWslUserActFor } from '../../../wsl/wsl-user-act-scope'
 
 const mocks = vi.hoisted(() => ({
   readWslDistroRunningState: vi.fn<() => Promise<'running' | 'stopped' | 'unverifiable'>>()
@@ -16,8 +17,11 @@ vi.mock('../../../wsl-background-distro-gate', async (importOriginal) => ({
 const WSL_CWD = '\\\\wsl.localhost\\Ubuntu\\home\\me\\repo'
 const hostPlatform = process.platform
 
-async function prepare(args: Partial<RuntimePtySpawnArgs>): Promise<void> {
-  const ctx = createRuntimePtySpawnState(makeRuntimePtySpawnTestDeps(), {
+async function prepare(
+  args: Partial<RuntimePtySpawnArgs>,
+  deps = makeRuntimePtySpawnTestDeps()
+): Promise<void> {
+  const ctx = createRuntimePtySpawnState(deps, {
     cols: 120,
     rows: 40,
     cwd: WSL_CWD,
@@ -61,3 +65,26 @@ describe("main's background start in a stopped WSL distro (E9)", () => {
     await expect(prepare({})).resolves.toBeUndefined()
   })
 })
+
+describe('host env prep after the startup hold (E9)', () => {
+  // Prep runs after the hold read; the distro may stop in between, so only a user act may wake it.
+  async function userActDuringPrep(args: Partial<RuntimePtySpawnArgs>): Promise<boolean[]> {
+    mocks.readWslDistroRunningState.mockResolvedValue('running')
+    const seen: boolean[] = []
+    const deps = makeRuntimePtySpawnTestDeps()
+    deps.prepareCodexResumeHome = () => {
+      seen.push(isWslUserActFor('Ubuntu'))
+      return null
+    }
+    await prepare({ command: 'codex', ...args }, deps)
+    return seen
+  }
+
+  it('gives a background start no user-act scope', async () => {
+    expect(await userActDuringPrep({})).toEqual([false])
+  })
+
+  it("keeps the user's start a user act", async () => {
+    expect(await userActDuringPrep({ wslUserAct: true })).toEqual([true])
+  })
+})
diff --git a/src/main/ipc/pty/runtime/spawn-preflight.ts b/src/main/ipc/pty/runtime/spawn-preflight.ts
index 91c54d93b2a..4eb8b07cf56 100644
--- a/src/main/ipc/pty/runtime/spawn-preflight.ts
+++ b/src/main/ipc/pty/runtime/spawn-preflight.ts
@@ -152,6 +152,8 @@ export async function prepareRuntimePtySpawn(
     mintedSessionId: ctx.requestedSessionId === undefined,
     resumeOnSelectedAccount: false,
     emptySessionIdSkipsHostEnv: true,
+    // The distro may stop after the hold read: a background start's prep must not wake it (E9).
+    wslPassiveRestore: args.wslUserAct !== true,
     requestedAgentTeamsPath: ctx.requestedAgentTeamsPath,
     provider: ctx.provider,
     deps: ctx.deps
diff --git a/src/main/providers/local-pty-spawn-environment-wsl-background.test.ts b/src/main/providers/local-pty-spawn-environment-wsl-background.test.ts
new file mode 100644
index 00000000000..545db6839e3
--- /dev/null
+++ b/src/main/providers/local-pty-spawn-environment-wsl-background.test.ts
@@ -0,0 +1,75 @@
+import { afterEach, beforeEach, describe, expect, it } from 'vitest'
+import { buildLocalPtySpawnEnvironment } from './local-pty-spawn-environment'
+import type { LocalPtyLaunchPlan } from './local-pty-launch-plan'
+import type { PtySpawnOptions } from './pty-provider-contract'
+import { runAsWslLaunchUserAct } from '../wsl/wsl-background-exec-gate'
+import { isWslUserActFor } from '../wsl/wsl-user-act-scope'
+
+const plan: LocalPtyLaunchPlan = {
+  startupAgentRecognition: null,
+  defaultCwd: '',
+  cwd: '\\\\wsl.localhost\\Ubuntu\\home\\me\\repo',
+  wslInfo: null,
+  worktreeWslContext: undefined,
+  preferredWslContext: undefined,
+  launchWslContext: undefined,
+  shellPath: 'wsl.exe',
+  shellArgs: [],
+  effectiveCwd: '',
+  validationCwd: '',
+  startupCommandDeliveredInShellArgs: false,
+  windowsFallbackAttempts: [],
+  shellReadyLaunch: null,
+  getFallbackShellReadyConfig: undefined,
+  primaryPreLaunchEnv: {},
+  isWslShell: true,
+  launchWslDistro: 'Ubuntu'
+}
+const hostPlatform = process.platform
+
+beforeEach(() => {
+  Object.defineProperty(process, 'platform', { configurable: true, value: 'win32' })
+})
+
+afterEach(() => {
+  Object.defineProperty(process, 'platform', { configurable: true, value: hostPlatform })
+})
+
+// The daemon-off builder wraps its env prep the way provider/local-configure.ts does.
+async function userActDuringDaemonOffPrep(spawn: Partial<PtySpawnOptions>): Promise<boolean[]> {
+  const seen: boolean[] = []
+  await buildLocalPtySpawnEnvironment({
+    id: 'pane',
+    spawn: { cols: 80, rows: 24, ...spawn },
+    getOptions: () => ({
+      buildSpawnEnv: (_id, baseEnv, ctx) =>
+        runAsWslLaunchUserAct(
+          {
+            isWsl: ctx?.isWsl === true,
+            passiveRestore: ctx?.wslPassiveRestore === true,
+            distro: ctx?.wslDistro
+          },
+          async () => {
+            seen.push(isWslUserActFor('Ubuntu'))
+            return baseEnv
+          }
+        )
+    }),
+    plan
+  })
+  return seen
+}
+
+describe("daemon-off env prep for main's background start (STA-12870, E9)", () => {
+  it('gives a background start no user-act scope', async () => {
+    expect(await userActDuringDaemonOffPrep({ wslBackgroundStart: true })).toEqual([false])
+  })
+
+  it('gives a passive restore no user-act scope', async () => {
+    expect(await userActDuringDaemonOffPrep({ wslPassiveRestore: true })).toEqual([false])
+  })
+
+  it("keeps the user's start a user act", async () => {
+    expect(await userActDuringDaemonOffPrep({})).toEqual([true])
+  })
+})
diff --git a/src/main/providers/local-pty-spawn-environment.ts b/src/main/providers/local-pty-spawn-environment.ts
index efcf7d661bc..14b99f33e7e 100644
--- a/src/main/providers/local-pty-spawn-environment.ts
+++ b/src/main/providers/local-pty-spawn-environment.ts
@@ -47,7 +47,8 @@ export function buildLocalPtySpawnEnvironment(args: {
     shellPath: plan.shellPath,
     isWsl: plan.isWslShell,
     wslDistro: plan.launchWslDistro,
-    wslPassiveRestore: spawn.wslPassiveRestore === true
+    // Main's background starts get the same E9 prep as a passive restore (STA-12870).
+    wslPassiveRestore: spawn.wslPassiveRestore === true || spawn.wslBackgroundStart === true
   })
 }