fix(worktrees): stop trusting a UNC ENOENT, which is what a shut-down distro looks like

Windows reports an unreachable 9P route as ENOENT, so a distro that has merely been shut down is
indistinguishable from one that never held any buckets. wsl.ts already refuses to trust a UNC
ENOENT for the same reason, probing inside the distro instead.

The classification added earlier called ENOENT a complete answer, which is right for a local home
that simply has no agent state but wrong here. After a wsl --shutdown the cached distro home still
resolves, so nothing else marked the scan incomplete: the empty result was memoized for the whole
process lifetime and every later generated create in that namespace reissued names spent inside
the distro. That is STA-4472 again, reached by a different route.

ENOENT now only means "absent" off UNC.

src/main/worktree-retirement-discovery-wsl.test.ts

@@ -109,6 +109,23 @@ describe('retirement discovery on WSL', () => {
     }
   })
 
+  it('does not trust a UNC ENOENT, which is what a shut-down distro looks like', async () => {
+    // Windows maps an unreachable 9P route to ENOENT, so `wsl --shutdown` is indistinguishable
+    // from a distro that never held buckets. The home stays cached and still resolves, so nothing
+    // else marks the scan incomplete — believing ENOENT here memoizes the STA-4472 hole for good.
+    const enoent = Object.assign(new Error('ENOENT'), { code: 'ENOENT' })
+    runWslTranscriptFsTaskMock.mockRejectedValue(enoent)
+
+    const retired = await discoverRetiredWorktreeNames({
+      workspaceRoots: [DISTRO_ROOT],
+      home: '/nonexistent-home',
+      env: {},
+      resolveWslHome: async () => '\\\\wsl.localhost\\Ubuntu\\home\\ada'
+    })
+
+    expect(retired.complete).toBe(false)
+  })
+
   it('stays retryable when the distro home cannot be resolved, rather than memoizing the hole', async () => {
     // `getWslHomeAsync` shells out to `wsl.exe` and returns null for a stopped or slow distro.
     // Memoizing that as a complete "nothing is retired" is the STA-4472 defect itself, since the

src/main/worktree-retirement-discovery.ts

@@ -1,6 +1,6 @@
 import { homedir } from 'node:os'
 import { join } from 'node:path'
-import { parseWslUncPath } from '../shared/wsl-paths'
+import { isWslUncPath, parseWslUncPath } from '../shared/wsl-paths'
 import {
   encodeClaudeProjectPaths,
   isClaudeProjectDirInScope
@@ -68,8 +68,14 @@ async function readDirectoryNames(path: string): Promise<{ names: string[]; refu
     // A missing root is itself a complete answer: the agent may never have run on this machine.
     // Anything else — a gate refusal, an EIO on a redirected or network home — leaves names
     // unread, and memoizing that as "nothing is retired" is the under-retiring direction.
+    //
+    // Never on UNC though: Windows reports an unreachable 9P route as ENOENT, so a distro that is
+    // merely shut down is indistinguishable from one that never held buckets. `wsl.ts` already
+    // refuses to trust a UNC ENOENT for the same reason. Believing it here would memoize the
+    // STA-4472 hole for the process lifetime, since the cached distro home still resolves.
     const code = (error as NodeJS.ErrnoException | null)?.code
-    return { names: [], refused: code !== 'ENOENT' && code !== 'ENOTDIR' }
+    const absent = code === 'ENOENT' || code === 'ENOTDIR'
+    return { names: [], refused: !absent || isWslUncPath(path) }
   }
 }