fix: recognize working WSL1 without a WSL2 kernel

src/main/wsl-availability.ts

@@ -1,5 +1,10 @@
 import { execFile, execFileSync } from 'node:child_process'
 import { resolveWslInteropSpawnCwd } from './wsl-interop-spawn-directory'
+import {
+  canExecuteWslWithoutKernel,
+  canExecuteWslWithoutKernelSync,
+  isWslMissingKernelError
+} from './wsl-missing-kernel-probe'
 
 type WslAvailabilityCache =
   | { available: true }
@@ -147,6 +152,9 @@ export function isWslAvailable(): boolean {
     })
     return cacheWslAvailabilityProbeResult(null, startedAtGeneration)
   } catch (error) {
+    if (isWslMissingKernelError(error) && canExecuteWslWithoutKernelSync()) {
+      return cacheWslAvailabilityProbeResult(null, startedAtGeneration)
+    }
     return cacheWslAvailabilityProbeResult(error, startedAtGeneration)
   }
 }
@@ -176,7 +184,12 @@ export function isWslAvailableAsync(): Promise<boolean> {
   const startedAtGeneration = wslAvailabilityCacheGeneration
   wslAvailabilityProbeInFlight = probeWslStatus()
     .then(() => cacheWslAvailabilityProbeResult(null, startedAtGeneration))
-    .catch((error: unknown) => cacheWslAvailabilityProbeResult(error, startedAtGeneration))
+    .catch(async (error: unknown) => {
+      if (isWslMissingKernelError(error) && (await canExecuteWslWithoutKernel())) {
+        return cacheWslAvailabilityProbeResult(null, startedAtGeneration)
+      }
+      return cacheWslAvailabilityProbeResult(error, startedAtGeneration)
+    })
     .finally(() => {
       wslAvailabilityProbeInFlight = null
     })

src/main/wsl-missing-kernel-probe.test.ts

@@ -0,0 +1,85 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+import { execFile, execFileSync } from 'node:child_process'
+import { runProcess, runProcessSync } from '../shared/child-process/run-process'
+import {
+  _resetWslAvailabilityCacheForTests,
+  isWslAvailable,
+  isWslAvailableAsync
+} from './wsl-availability'
+
+vi.mock('node:child_process', () => ({ execFile: vi.fn(), execFileSync: vi.fn() }))
+vi.mock('../shared/child-process/run-process', () => ({
+  runProcess: vi.fn(),
+  runProcessSync: vi.fn()
+}))
+vi.mock('./wsl-interop-spawn-directory', () => ({
+  resolveWslInteropSpawnCwd: () => 'C:\\Windows'
+}))
+
+const originalPlatform = process.platform
+const success = { code: 0, signal: null, stdout: '', stderr: '', timedOut: false }
+
+beforeEach(() => {
+  vi.resetAllMocks()
+  Object.defineProperty(process, 'platform', { value: 'win32' })
+  _resetWslAvailabilityCacheForTests()
+})
+afterEach(() => {
+  Object.defineProperty(process, 'platform', { value: originalPlatform })
+  _resetWslAvailabilityCacheForTests()
+})
+
+for (const mode of ['sync', 'async'] as const) {
+  describe(`${mode} WSL1 availability without WSL2 kernel`, () => {
+    const probe = () => (mode === 'sync' ? isWslAvailable() : isWslAvailableAsync())
+    function failStatus(code: number): void {
+      vi.mocked(execFileSync).mockImplementation(() => {
+        throw { status: code }
+      })
+      vi.mocked(execFile).mockImplementation((...args: unknown[]) => {
+        const callback = args.at(-1) as (error: unknown) => void
+        callback({ code })
+        return {} as ReturnType<typeof execFile>
+      })
+    }
+    function guestResult(result: typeof success): void {
+      vi.mocked(runProcess).mockResolvedValue(result)
+      vi.mocked(runProcessSync).mockReturnValue(result)
+    }
+
+    it('requires guest execution and caches its success', async () => {
+      failStatus(-444)
+      guestResult(success)
+      expect(await probe()).toBe(true)
+      expect(await probe()).toBe(true)
+      const runner = mode === 'sync' ? runProcessSync : runProcess
+      expect(runner).toHaveBeenCalledTimes(1)
+      expect(runner).toHaveBeenCalledWith(
+        expect.objectContaining({
+          program: 'wsl.exe',
+          args: ['--exec', '/bin/true'],
+          timeoutMs: 5000,
+          cwd: 'C:\\Windows'
+        })
+      )
+    })
+
+    for (const result of [
+      { ...success, code: 1 },
+      { ...success, timedOut: true }
+    ]) {
+      it(`keeps failed guest unavailable: ${JSON.stringify(result)}`, async () => {
+        failStatus(-444)
+        guestResult(result)
+        expect(await probe()).toBe(false)
+      })
+    }
+
+    it('does not probe a guest for unrelated status failures', async () => {
+      failStatus(1)
+      expect(await probe()).toBe(false)
+      expect(runProcess).not.toHaveBeenCalled()
+      expect(runProcessSync).not.toHaveBeenCalled()
+    })
+  })
+}

src/main/wsl-missing-kernel-probe.ts

@@ -0,0 +1,37 @@
+import { runProcess, runProcessSync, type ProcessSpec } from '../shared/child-process/run-process'
+import { buildWslExecArgs } from '../shared/wsl-login-shell-command'
+import { resolveWslInteropSpawnCwd } from './wsl-interop-spawn-directory'
+
+export function isWslMissingKernelError(error: unknown): boolean {
+  const failure = error as { code?: unknown; status?: unknown } | null
+  return failure?.code === -444 || failure?.status === -444
+}
+
+function defaultGuestProbe(): ProcessSpec {
+  return {
+    program: 'wsl.exe',
+    args: buildWslExecArgs(undefined, ['/bin/true']),
+    cwd: resolveWslInteropSpawnCwd(),
+    timeoutMs: 5000,
+    maxOutputBytes: 4096
+  }
+}
+
+// WSL1 can execute normally while --status rejects a missing WSL2 kernel.
+export async function canExecuteWslWithoutKernel(): Promise<boolean> {
+  try {
+    const result = await runProcess(defaultGuestProbe())
+    return result.code === 0 && !result.timedOut
+  } catch {
+    return false
+  }
+}
+
+export function canExecuteWslWithoutKernelSync(): boolean {
+  try {
+    const result = runProcessSync(defaultGuestProbe())
+    return result.code === 0 && !result.timedOut
+  } catch {
+    return false
+  }
+}